Chapter Editors: Knut Ringen, Jane L. Seegal and James L. Weeks
Table of Contents
Health and Safety Hazards in the Construction Industry
James L. Weeks
Health Risks of Underground Construction Work
Organizational Factors Affecting Health and Safety
Doug J. McVittie
Integrating Prevention and Quality Management
Types of Projects and their Associated Hazards
Jack L. Mickle
Scott P. Schneider
Equipment, Machinery and Material
Hans Göran Linder
Elevators, Escalators and Hoists
J. Staal and John Quackenbush
Cement and Concrete
L. Prodan and G. Bachofen
James L. Weeks
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Construction workers build, repair, maintain, renovate, modify and demolish houses, office buildings, temples, factories, hospitals, roads, bridges, tunnels, stadiums, docks, airports and more. The International Labour Organization (ILO) classifies the construction industry as government and private-sector firms erecting buildings for habitation or for commercial purposes and public works such as roads, bridges, tunnels, dams or airports. In the United States and some other countries, construction workers also clean hazardous waste sites.
Construction as a proportion of gross domestic product varies widely in industrialized countries. It is about 4% of GDP in the United States, 6.5% in Germany and 17% in Japan. In most countries, employers have relatively few full-time employees. Many companies specialize in skilled trades—electricity, plumbing or tile setting, for instance—and work as subcontractors.
The Construction Labour Force
A large portion of construction workers are unskilled labourers; others are classified in any of several skilled trades (see table 1). Construction workers include about 5 to 10% of the workforce in industrialized countries. Throughout the world, over 90% of construction workers are male. In some developing countries, the proportion of women is higher and they tend to be concentrated in unskilled occupations. In some countries, the work is left to migrant workers, and in others, the industry provides relatively well-paid employment and an avenue to financial security. For many, unskilled construction work is the entry into the paid labour force in construction or other industries.
Work Organization and Labour Instability
Construction projects, especially large ones, are complex and dynamic. Several employers may work on one site simultaneously, with the mix of contractors changing with the phases of the project; for example, the general contractor is present at all times, excavating contractors early, then carpenters, electricians and plumbers, followed by floor finishers, painters and landscapers. And as the work develops—for instance, as a building’s walls are erected, as the weather changes or as a tunnel advances—the ambient conditions such as ventilation and temperature change too.
Construction workers typically are hired from project to project and may spend only a few weeks or months at any one project. There are consequences for both workers and work projects. Workers must make and remake productive and safe working relationships with other workers whom they may not know, and this may affect safety at the work site. And in the course of the year, construction workers may have several employers and less than full employment. They might work an average of only 1,500 hours in a year while workers in manufacturing, for example, are more likely to work regular 40 hour weeks and 2,000 hours per year. In order to make up for slack time, many construction workers have other jobs—and exposure to other health or safety hazards—outside of construction.
For a particular project, there is frequent change in the number of workers and the composition of the labour force at any one site. This change results both from the need for different skilled trades at different phases of a work project and from the high turnover of construction workers, particularly unskilled workers. At any one time, a project may include a large proportion of inexperienced, temporary and transient workers who may not be fluent in the common language. Although construction work often must be done in teams, it is difficult to develop effective, safe teamwork under such conditions.
Like the workforce, the universe of construction contractors is marked by high turnover and consists mainly of small operations. Of the 1.9 million construction contractors in the United States identified by the 1990 Census, only 28% had any full-time employees. Just 136,000 (7%) had 10 or more employees. The degree of contractor participation in trade organizations varies by country. In the United States, only about 10 to 15% of contractors participate; in some European countries, this proportion is higher but still involves less than half of contractors. This makes it difficult to identify contractors and inform them of their rights and responsibilities under pertinent health and safety or any other legislation or regulations.
As in some other industries, an increasing proportion of contractors in the United States and Europe consists of individual workers hired as independent contractors by prime- or sub-contractors who employ workers. Ordinarily, an employing contractor does not provide subcontractors with health benefits, workers’ compensation coverage, unemployment insurance, pension benefits or other benefits. Nor do prime contractors have any obligation to subcontractors under health and safety regulations; these regulations govern rights and responsibilities as they apply to their own employees. This arrangement gives some independence to individuals who contract for their services, but at the cost of removing a wide range of benefits. It also relieves employing contractors of the obligation to provide mandated benefits to individuals who are contractors. This private arrangement subverts public policy and has been successfully challenged in court, yet it persists and may become more of a problem for the health and safety of workers on the job, regardless of their employment relationship. The US Bureau of Labor Statistics (BLS) estimates that 9% of the US workforce is self-employed, but in construction as many as 25% of workers are self-employed independent contractors.
Health Hazards on Construction Sites
Construction workers are exposed to a wide variety of health hazards on the job. Exposure differs from trade to trade, from job to job, by the day, even by the hour. Exposure to any one hazard is typically intermittent and of short duration, but is likely to reoccur. A worker may not only encounter the primary hazards of his or her own job, but may also be exposed as a bystander to hazards produced by those who work nearby or upwind. This pattern of exposure is a consequence of having many employers with jobs of relatively short duration and working alongside workers in other trades that generate other hazards. The severity of each hazard depends on the concentration and duration of exposure for that particular job. Bystander exposures can be approximated if one knows the trade of workers nearby. Hazards present for workers in particular trades are listed in table 2.
Table 2. Primary hazards encountered in skilled construction trades.
Each trade is listed below with an indication of the primary hazards to which a worker in that trade might be exposed. Exposure may occur to either supervisors or to wage earners. Hazards that are common to nearly all construction-heat, risk factors for musculoskeletal disorders and stress-are not listed.
The classifications of construction trades used here are those used in the United States. It includes the construction trades as classified in the Standard Occupational Classification system developed by the US Department of Commerce. This system classifies the trades by the principal skills inherent in the trade.
Cement dermatitis, awkward postures, heavy loads
Cement dermatitis, awkward postures, heavy loads
Hard tile setters
Vapour from bonding agents, dermatitis, awkward postures
Wood dust, heavy loads, repetitive motion
Plaster dust, walking on stilts, heavy loads, awkward postures
Heavy metals in solder fumes, awkward posture, heavy loads, asbestos dust
Electrical power installers and repairers
Heavy metals in solder fumes, heavy loads, asbestos dust
Solvent vapours, toxic metals in pigments, paint additives
Vapours from glue, awkward postures
Dermatitis, awkward postures
Lead fumes and particles, welding fumes
Lead fumes and particles, welding fumes, asbestos dust
Welding fumes, asbestos dust
Knee trauma, awkward postures, glue and glue vapour
Soft tile installers
Concrete and terrazzo finishers
Asbestos, synthetic fibres, awkward postures
Paving, surfacing and tamping equipment operators
Asphalt emissions, gasoline and diesel engine exhaust, heat
Rail- and track-laying equipment operators
Silica dust, heat
Roofing tar, heat, working at heights
Sheetmetal duct installers
Awkward postures, heavy loads, noise
Structural metal installers
Awkward postures, heavy loads, working at heights
Metal fumes, lead, cadmium
Drillers, earth, rock
Silica dust, whole-body vibration, noise
Air hammer operators
Noise, whole-body vibration, silica dust
Pile driving operators
Noise, whole-body vibration
Hoist and winch operators
Noise, lubricating oil
Crane and tower operators
Excavating and loading machine operators
Silica dust, histoplasmosis, whole-body vibration, heat stress, noise
Grader, dozer and scraper operators
Silica dust, whole-body vibration, heat noise
Highway and street construction workers
Asphalt emissions, heat, diesel engine exhaust
Truck and tractor equipment operators
Whole-body vibration, diesel engine exhaust
Asbestos, lead, dust, noise
Hazardous waste workers
As in other jobs, hazards for construction workers are typically of four classes: chemical, physical, biological and social.
Chemical hazards are often airborne and can appear as dusts, fumes, mists, vapours or gases; thus, exposure usually occurs by inhalation, although some airborne hazards may settle on and be absorbed through the intact skin (e.g., pesticides and some organic solvents). Chemical hazards also occur in liquid or semi-liquid state (e.g., glues or adhesives, tar) or as powders (e.g., dry cement). Skin contact with chemicals in this state can occur in addition to possible inhalation of the vapour resulting in systemic poisoning or contact dermatitis. Chemicals might also be ingested with food or water, or might be inhaled by smoking.
Several illnesses have been linked to the construction trades, among them:
Elevated death rates from cancer of the lung and respiratory tree have been found among asbestos insulation workers, roofers, welders and some woodworkers. Lead poisoning occurs among bridge rehabilitation workers and painters, and heat stress (from wearing full-body protective suits) among hazardous-waste clean-up workers and roofers. White finger (Raynaud’s syndrome) appears among some jackhammer operators and other workers who use vibrating drills (e.g., stoper drills among tunnellers).
Alcoholism and other alcohol-related disease is more frequent than expected among construction workers. Specific occupational causes have not been identified, but it is possible that it is related to stress resulting from lack of control over employment prospects, heavy work demands or social isolation due to unstable working relationships.
Physical hazards are present in every construction project. These hazards include noise, heat and cold, radiation, vibration and barometric pressure. Construction work often must be done in extreme heat or cold, in windy, rainy, snowy, or foggy weather or at night. Ionizing and non-ionizing radiation is encountered, as are extremes of barometric pressure.
The machines that have transformed construction into an increasingly mechanized activity have also made it increasingly noisy. The sources of noise are engines of all kinds (e.g., on vehicles, air compressors and cranes), winches, rivet guns, nail guns, paint guns, pneumatic hammers, power saws, sanders, routers, planers, explosives and many more. Noise is present on demolition projects by the very activity of demolition. It affects not only the person operating a noise-making machine, but all those close-by and not only causes noise-induced hearing loss, but also masks other sounds that are important for communication and for safety.
Pneumatic hammers, many hand tools and earth-moving and other large mobile machines also subject workers to segmental and whole-body vibration.
Heat and cold hazards arise primarily because a large portion of construction work is conducted while exposed to the weather, the principal source of heat and cold hazards. Roofers are exposed to the sun, often with no protection, and often must heat pots of tar, thus receiving both heavy radiant and convective heat loads in addition to metabolic heat from physical labour. Heavy equipment operators may sit beside a hot engine and work in an enclosed cab with windows and without ventilation. Those that work in an open cab with no roof have no protection from the sun. Workers in protective gear, such as that needed for removal of hazardous waste, may generate metabolic heat from hard physical labour and get little relief since they may be in an air-tight suit. A shortage of potable water or shade contributes to heat stress as well. Construction workers also work in especially cold conditions during the winter, with danger of frostbite and hypothermia and risk of slipping on ice.
The principal sources of non-ionizing ultraviolet (UV) radiation are the sun and electric arc welding. Exposure to ionizing radiation is less common, but can occur with x-ray inspection of welds, for example, or it may occur with instruments such as flow meters that use radioactive isotopes. Lasers are becoming more common and may cause injury, especially to the eyes, if the beam is intercepted.
Those who work under water or in pressurized tunnels, in caissons or as divers are exposed to high barometric pressure. Such workers are at risk of developing a variety of conditions associated with high pressure: decompression sickness, inert gas narcosis, aseptic bone necrosis and other disorders.
Strains and sprains are among the most common injuries among construction workers. These, and many chronically disabling musculoskeletal disorders (such as tendinitis, carpal tunnel syndrome and low-back pain) occur as a result of either traumatic injury, repetitive forceful movements, awkward postures or overexertion (see figure 1). Falls due to unstable footing, unguarded holes and slips off scaffolding (see figure 2) and ladders are very common.
Figure 1. Carrying without appropriate work clothing and protective equipment.
Figure 2. Unsafe scaffolding in Kathmandu, Nepal, 1974
Biological hazards are presented by exposure to infectious micro-organisms, to toxic substances of biological origin or animal attacks. Excavation workers, for example, can develop histoplasmosis, an infection of the lung caused by a common soil fungus. Since there is constant change in the composition of the labour force on any one project, individual workers come in contact with other workers and, as a consequence, may become infected with contagious diseases—influenza or tuberculosis, for example. Workers may also be at risk of malaria, yellow fever or Lyme disease if work is conducted in areas where these organisms and their insect vectors are prevalent.
Toxic substances of plant origin come from poison ivy, poison oak, poison sumac and nettles, all of which can cause skin eruptions. Some wood dusts are carcinogenic, and some (e.g., western red cedar) are allergenic.
Attacks by animals are rare but may occur whenever a construction project disturbs them or encroaches on their habitat. This could include wasps, hornets, fire ants, snakes and many others. Underwater workers may be at risk from attack by sharks or other fish.
Social hazards stem from the social organization of the industry. Employment is intermittent and constantly changing, and control over many aspects of employment is limited because construction activity is dependent on many factors over which construction workers have no control, such as the state of an economy or the weather. Because of the same factors, there can be intense pressure to become more productive. Since the workforce is constantly changing, and with it the hours and location of work, and many projects require living in work camps away from home and family, construction workers may lack stable and dependable networks of social support. Features of construction work such as heavy workload, limited control and limited social support are the very factors associated with increased stress in other industries. These hazards are not unique to any trade, but are common to all construction workers in one way or another.
Evaluating either primary or bystander exposure requires knowing the tasks being done and the composition of ingredients and by-products associated with each job or task. This knowledge usually exists somewhere (e.g., material safety data sheets, MSDSs) but may not be available at the job site. With continually evolving computer and communications technology, it is relatively easy to obtain such information and make it available.
Controlling Occupational Hazards
Measuring and evaluating exposure to occupational hazards requires consideration of the novel manner in which construction workers are exposed. Conventional industrial hygiene measurements and exposure limits are based on 8-hour time-weighted averages. But since exposures in construction are usually brief, intermittent, varied but likely to be repeated, such measures and exposure limits are not as useful as in other jobs. Exposure measurement can be based on tasks rather than shifts. With this approach, separate tasks can be identified and hazards characterized for each. A task is a limited activity such as welding, soldering, sanding drywall, painting, installing plumbing and so on. As exposures are characterized for tasks, it should be possible to develop an exposure profile for an individual worker with knowledge of the tasks he or she performed or was near enough to be exposed to. As knowledge of task-based exposure increases, one may develop task-based controls.
Exposure varies with the concentration of the hazard and the frequency and duration of the task. As a general approach to hazard control, it is possible to reduce exposure by reducing the concentration or the duration or frequency of the task. Since exposure in construction is already intermittent, administrative controls that rely on reducing the frequency or duration of exposure are less practical than in other industries. Consequently, the most effective way to reduce exposure is to reduce the concentration of hazards. Other important aspects of controlling exposure include provisions for eating and sanitary facilities and education and training.
Decreasing exposure concentration
For reducing exposure concentration, it is useful to consider the source, the environment in which a hazard occurs and the workers who are exposed. As a general rule, the closer controls are to a source, the more efficient and effective they are. Three general types of controls can be used to reduce the concentration of occupational hazards. These are, from most to least effective:
Hazards originate at a source. The most efficient way to protect workers from hazards is to change the primary source with some sort of engineering change. For example, a less hazardous substance can be substituted for one that is more hazardous. Non-respirable synthetic vitreous fibres can be substituted for asbestos, and water can be substituted for organic solvents in paints. Similarly, non-silica abrasives can replace sand in abrasive blasting (also known as sand blasting). Or a process can be fundamentally changed, such as by replacing pneumatic hammers with impact hammers that generate less noise and vibration. If sawing or drilling generates harmful dusts, particulate matter or noise, these processes could be done by shear cutting or punching. Technological improvements are reducing the risks of some musculoskeletal and other health problems. Many of the changes are straightforward—for example, a two-handed screwdriver with a longer handle increases torque on the object and reduces stress on the wrists.
Environmental controls are used to remove a hazardous substance from the environment, if the substance is airborne, or to shield the source, if it is a physical hazard. Local exhaust ventilation (LEV) can be used at a particular job with a ventilation duct and a hood to capture the fumes, vapours or dust. However, since the location of tasks that emit toxic materials changes, and because the structure itself changes, any LEV would have to be mobile and flexible in order to accommodate these changes. Mobile truck-mounted dust collectors with fans and filters, independent power sources, flexible ducts and mobile water supplies have been used on many job sites to provide LEV for a variety of hazard-producing processes.
The simple and effective method for controlling exposure to radiant physical hazards (noise, ultraviolet (UV) radiation from arc welding, infrared radiant (IR) heat from hot objects) is to shield them with some appropriate material. Plywood sheets shield IR and UV radiation, and material that absorbs and reflects sound will provide some protection from noise sources.
Major sources of heat stress are weather and hard physical labour. Adverse effects from heat stress can be avoided through reductions in the workload, provision of water and adequate breaks in the shade and, possibly, night work.
When engineering controls or changes in work practices do not adequately protect workers, workers may need to use personal protective equipment (PPE) (see figure 3). In order for such equipment to be effective, workers must be trained in its use, and the equipment must fit properly and be inspected and maintained. Furthermore, if others who are in the vicinity may be exposed to the hazard, they should either be protected or prevented from entering the area.
Figure 3. Construction worker in Nairobi, Kenya, without foot protection or hard hat
The use of some personal controls can create problems. For instance, construction workers often perform as teams and thus have to communicate with each other, but respirators interfere with communication. And full-body protective gear can contribute to heat stress because it is heavy and because body heat is not allowed to dissipate.
Having protective gear without knowing its limitations can also give workers or employers the illusion that the workers are protected when, with certain exposure conditions, they are not protected. For instance, there are no gloves currently available that protect for more than 2 hours against methylene chloride, a common ingredient in paint strippers. And there are few data on whether gloves protect against solvent mixtures such as those containing both acetone and toluene or both methanol and xylene. The level of protection depends on how a glove is used. In addition, gloves are generally tested on one chemical at a time and rarely for more than 8 hours.
Eating and sanitary facilities
A lack of eating and sanitary facilities may also lead to increased exposures. Often, workers cannot wash before meals and must eat in the work zone, which means they may inadvertently swallow toxic substances transferred from their hands to food or cigarettes. A lack of changing facilities at a worksite may result in transport of contaminants from the workplace to a worker’s home.
Injuries and Illnesses in Construction
Because construction involves a large proportion of the workforce, construction fatalities also affect a large population. For instance, in the United States, construction represents 5 to 6% of the workforce but accounts for 15% of work-related fatalities—more than any other sector. The construction sector in Japan is 10% of the workforce but has 42% of the work-related deaths; in Sweden, the numbers are 6% and 13%, respectively.
The most common fatal injuries among construction workers in the United States are falls (30%), transportation accidents (26%), contact with objects or equipment (e.g., struck by an object or caught in machinery or materials) (19%) and exposure to harmful substances (18%), most of which (75%) are electrocutions from contact with electrical wiring, overhead power lines or electrically powered machinery or hand tools. These four types of events account for nearly all (93%) fatal injuries among construction workers in the United States (Pollack et al. 1996).
Among trades in the US, the rate of fatal injuries is highest among structural steel workers (118 fatalities per 100,000 full-time equivalent workers for 1992–1993 compared to a rate of 17 per 100,000 for other trades combined) and 70% of structural steel worker fatalities were from falls. Labourers experienced the greatest number of fatalities, with an annual average number of about 200. Overall, the rate of fatalities was highest for workers 55 years and older.
The proportion of fatalities by event differed for each trade. For supervisors, falls and transportation accidents accounted for about 60% of all fatalities. For carpenters, painters, roofers and structural steel workers, falls were most common, accounting for 50, 55, 70 and 69% of all fatalities for those trades, respectively. For operating engineers and excavating machine operators, transportation accidents were the most common causes, accounting for 48 and 65% of fatalities for those trades, respectively. Most of these were associated with dump trucks. Fatalities from improperly sloped or shored trenches continue to be a major cause of fatalities (McVittie 1995). The primary hazards in the skilled trades are listed in table 2.
Table 3. Construction occupations with excess standardized mortality rates (SMRs)and standardized incidence rates (SIRs) for selected causes.
Significantly higher SMRs
Significantly higher SIRs
All causes,* all cancers,* stomach cancer, violent death,* accidental falls
Lip cancer, stomach and larynx cancer,*a lung cancerb
All causes,* cardiovascular*
All causes,* lung cancer, pneumoconiosis, violent death*
Peritoneal tumour, lung cancer
Cardiovascular,* other accidents
All cancers,* lung cancer, pneumoconiosis
All cancers, pleural tumour, lung cancer
All causes,* cardiovascular,*
Sheet metal workers
All cancers,* lung cancer, accidental falls
All cancers, lung cancer
Nose and nasal sinus cancer
* Cancers or causes of death are significantly higher in comparison to all other occupational groups combined. “Other accidents” includes typical work-related injuries.
a The relative risk for larynx cancer among concrete workers, compared to carpenters, is 3 times higher.
b The relative risk for lung cancer among concrete workers, compared to carpenters, is almost double.
Source: Engholm and Englund 1995.
Disabling or lost time injuries
In the United States and Canada, the most common causes of lost time injuries are overexertion; being struck by an object; falls to a lower level; and slips, trips and falls on the same level. The most common category of injury is strains and sprains, some of which become sources of chronic pain and impairment. The activities most often associated with lost time injuries are manual materials handling and installation (e.g., installing dry-wall, piping or ventilation duct-work). Injuries occurring in transit (e.g., walking, climbing, descending) are also common. Underlying many of these injuries is the problem of housekeeping. Many slips, trips and falls are caused by walking through construction debris.
Costs of Injuries and Illness
Occupational injuries and illnesses in construction are very costly. Estimates for the cost of injuries in construction in the US range from $10 billion to $40 billion annually (Meridian Research 1994); at $20 billion, the cost per construction worker would be US$3,500 yearly. Workers’ compensation premiums for three trades—carpenters, masons and structural iron workers— averaged 28.6% of payroll nationally in mid-1994 (Powers 1994). Premium rates vary enormously, depending on trade and jurisdiction. The average premium cost is several times higher than in most industrialized countries, where workers’ compensation insurance premiums range from 3 to 6% of payroll. In addition to workers’ compensation, there are liability insurance premiums and other indirect costs, including reduced work crew efficiency, clean-up (from a cave-in or collapse, for instance) or overtime necessitated by an injury. Such indirect costs can be several times the workers’ compensation award.
Management for Safe Construction Work
Effective safety programmes have several features in common. They are manifest throughout organizations, from the highest offices of a general contractor to project managers, supervisors, union officials and workers on the job. Codes of practice are conscientiously implemented and evaluated. Costs of injury and illness are calculated and performance is measured; those that do well are rewarded, those that do not are penalized. Safety is an integral part of contracts and subcontracts. Everybody—managers, supervisors and workers—receives general, site-specific and site-relevant training and re-training. Inexperienced workers receive on-the-job training from experienced workers. In projects where such measures are implemented, injury rates are significantly lower than on otherwise comparable sites.
Preventing Accidents and Injuries
Entities in the industry with lower injury rates share several common characteristics: they have a clearly defined policy statement that applies throughout the organization, from top management to the project site. This policy statement refers to a specific code of practice that describes, in detail, the hazards and their control for the pertinent occupations and tasks at a site. Responsibilities are clearly assigned and standards of performance are stated. Failures to meet these standards are investigated and penalties imposed as appropriate. Meeting or exceeding standards is rewarded. An accounting system is used that shows the costs of each injury or accident and the benefits of injury prevention. Employees or their representatives are involved in establishing and administering a programme of injury prevention. Involvement often occurs in the formation of a joint labour or worker management committee. Physical examinations are performed to determine workers’ fitness for duty and job assignment. These exams are provided when first employed and when returning from a disability or other layoff.
Hazards are identified, analysed and controlled following the classes of hazards discussed in other articles in this chapter. The entire work site is inspected on a regular basis and results are recorded. Equipment is inspected to ensure its safe operation (e.g., brakes on vehicles, alarms, guards and so on). Injury hazards include those associated with the most common types of lost-time injuries: falls from heights or at the same level, lifting or other forms of manual materials handling, risk of electrocution, risk of injury associated with either highway or off-road vehicles, trench cave-ins and others. Health hazards would include airborne particles (such as silica, asbestos, synthetic vitreous fibres, diesel particulates), gases and vapours (such as carbon monoxide, solvent vapour, engine exhaust), physical hazards (such as noise, heat, hyperbaric pressure) and others, such as stress.
Preparations are made for emergency situations and emergency drills are conducted as needed. Preparations would include assignment of responsibilities, provision of first aid and immediate medical attention at the site, communication at the site and with others off the site (such as ambulances, family members, home offices and labour unions), transportation, designation of health care facilities, securing and stabilizing the environment where the emergency occurred, identifying witnesses and documenting events. As needed, emergency preparedness would also cover means of escape from an uncontrolled hazard such as fire or flood.
Accidents and injuries are investigated and recorded. The purpose of reports is to identify causes that could have been controlled so that, in the future, similar occurrences can be prevented. Reports should be organized with a standardized record-keeping system to better facilitate analysis and prevention. To facilitate comparison of injury rates from one situation to another, it is useful to identify the pertinent population of workers within which an injury occurred, and their hours worked, in order to calculate an injury rate (i.e., the number of injuries per hour worked or the number of hours worked between injuries).
Workers and supervisors receive training and education in safety. This education consists of teaching general principles of safety and health, is integrated into task training, is specific for each work site and covers procedures to follow in the event of an accident or injury. Education and training for workers and supervisors is an essential part of any effort to prevent injuries and disease. Training about safe work practices and procedures have been provided in many countries by some companies and trade unions. These procedures, include lockout and tagout of electrical power sources during maintenance procedures, use of lanyards while working at heights, shoring trenches, providing safe walking surfaces and so on. It is also important to provide site-specific training, covering unique features about the job site such as means of entry and exit. Training should include instruction about dangerous substances. Performance or hands-on training, demonstrating that one knows safe practices, is much better for instilling safe behaviour than classroom instruction and written examination.
In the United States, training about certain hazardous substances is mandated by federal law. The same concern in Germany led to development of the Gefahrstoff-Informationssystem der Berufsgenossenschaften der Bauwirtschaft, or GISBAU, programme. GISBAU works with manufacturers to determine the content of all substances used on construction sites. Equally important, the programme provides the information in a form to suit the differing needs of health staff, managers and workers. The information is available through training programmes, in print and on computer terminals at work sites. GISBAU gives advice about how to substitute for some hazardous substances and tells how to safely handle others. (See the chapter Using, storing and transporting chemicals.)
Information about chemical, physical and other health hazards is available at the work site in the languages that workers use. If workers are to work intelligently on the job, they should have the information necessary to decide what to do in specific situations.
And finally, contracts between contractors and subcontractors should include safety features. Provisions could include establishing a unified safety organization at multi-employer work sites, performance requirements and rewards and penalties.
Underground construction work includes tunnelling for roads, highways and railroads and laying pipelines for sewers, hot water, steam, electrical conduits, telephone lines. Hazards in this work include hard physical labour, crystalline silica dust, cement dust, noise, vibration, diesel engine exhaust, chemical vapours, radon and oxygen-deficient atmospheres. Occasionally this work must be done in a pressurized environment. Underground workers are at risk for serious and often fatal injuries. Some hazards are the same as those of construction on the surface, but they are amplified by working in a confined environment. Other hazards are unique to underground work. These include being struck by specialized machinery or being electrocuted, being buried by roof falls or cave-ins and being asphyxiated or injured by fires or explosions. Tunnelling operations may encounter unexpected impoundments of water, resulting in floods and drowning.
The construction of tunnels requires a great deal of physical effort. Energy expenditure during manual work is usually from 200 to 350 W, with a great part of static load of the muscles. Heart rate during work with compressed-air drills and pneumatic hammers reaches 150 to 160 per minute. Work is often done in unfavourable cold and humid microclimatic conditions, sometimes in cumbersome work postures. It is usually combined with exposure to other risk factors which depend on the local geological conditions and on the type of technology used. This heavy workload can be an important contribution to heat stress.
The need for heavy manual labour can be reduced by mechanization. But mechanization brings its own hazards. Large and powerful mobile machines in a confined environment introduce risks of serious injury to persons working nearby, who may be struck or crushed. Underground machinery also may generate dust, noise, vibration and diesel exhaust. Mechanization also results in fewer jobs, which reduces the number of persons exposed but at the expense of unemployment and all of its attendant problems.
Crystalline silica (also known as free silica and quartz) occurs naturally in many different types of rock. Sandstone is practically pure silica; granite may contain 75%; shale, 30%; and slate, 10%. Limestone, marble and salt are, for practical purposes, completely free of silica. Considering that silica is ubiquitous in the earth’s crust, dust samples should be taken and analysed at least at the start of an underground job and whenever the type of rock changes as work progresses through it.
Respirable silica dust is generated whenever silica-bearing rock is crushed, drilled, ground or otherwise pulverized. The main sources of airborne silica dust are compressed-air drills and pneumatic hammers. Work with these tools most often occurs in the fore part of the tunnel and, therefore, workers in these areas are the most heavily exposed. Dust suppression technology should be applied in all instances.
Blasting generates not only flying debris, but also dust and nitrogen oxides. To prevent excessive exposure, the customary procedure is to prevent re-entry to the affected area until the dust and gases have cleared. A common procedure is to blast at the end of the last work shift of the day and to clear out debris during the next shift.
Cement dust is generated when cement is mixed. This dust is a respiratory and mucous membrane irritant in high concentrations, but chronic effects have not been observed. When it settles on skin and mixes with sweat, however, cement dust can cause dermatoses. When wet concrete is sprayed in place, it too can cause dermatoses.
Noise can be significant in underground construction work. Principal sources include pneumatic drills and hammers, diesel engines and fans. Since the underground work environment is confined, there is also considerable reverberant noise. Peak noise levels can exceed 115 dBA, with time-weighted average noise exposure equivalent to 105 dBA. Noise-reducing technology is available for most equipment and should be applied.
Underground construction workers can also be exposed to whole-body vibration from mobile machinery and to hand-arm vibration from pneumatic drills and hammers. The levels of acceleration transmitted to the hands from pneumatic tools can reach about 150 dB (comparable to 10 m/s2). Harmful effects of hand-arm vibration can be aggravated by a cold and damp working environment.
If soil is highly saturated with water or if construction is conducted under water, the work environment may have to be pressurized to keep water out. For underwater work, caissons are used. When workers in such a hyperbaric environment make too rapid a transition to normal air pressure, they risk decompression sickness and related disorders. Since the absorption of most toxic gases and vapours depends on their partial pressure, more may be absorbed at higher pressure. Ten ppm of carbon monoxide (CO) at 2 atmospheres of pressure, for example, will have the effect of 20 ppm CO at 1 atmosphere.
Chemicals are used in underground construction in a variety of ways. For example, insufficiently coherent layers of rock may be stabilized with an infusion of urea formaldehyde resin, polyurethane foam or mixtures of sodium water glass with formamide or with ethyl and butyl acetate. Consequently, vapours of formaldehyde, ammonia, ethyl or butyl alcohol or di-isocyanates may be found in the tunnel atmosphere during application. Following application, these contaminants may escape into the tunnel from the surrounding walls, and it may therefore be difficult to fully control their concentrations, even with intensive mechanical ventilation.
Radon occurs naturally in some rock and may leak into the work environment, where it will decay into other radioactive isotopes. Some of these are alpha emitters that may be inhaled and increase the risk of lung cancer.
Tunnels constructed in inhabited areas can also be contaminated with substances from surrounding pipes. Water, heating and cooking gas, fuel oil, petrol and so on may leak into a tunnel or, if pipes carrying these substances are broken during excavation, they may escape into the work environment.
The construction of vertical shafts using mining technology poses similar health problems to those of tunnelling. In terrain where organic substances are present, products of microbiological decomposition may be expected.
Maintenance work in tunnels used for traffic differs from similar work on the surface mainly in the difficulty of installing safety and control equipment, for example, ventilation for electric arc welding; this may influence the quality of safety measures. Work in tunnels in which pipelines for hot water or steam are present is associated with great heat load, demanding a special regime of work and breaks.
Oxygen deficiency may occur in tunnels either because oxygen is displaced by other gases or because it is consumed by microbes or by the oxidation of pyrites. Microbes may also release methane or ethane, which not only displace oxygen but, in sufficient concentration, may create the risk of explosion. Carbon dioxide (commonly called blackdamp in Europe) is also generated by microbial contamination. The atmospheres in spaces which have been closed for a long time may contain mostly nitrogen, practically no oxygen and 5 to 15% carbon dioxide.
Blackdamp penetrates into the shaft from the surrounding terrain due to changes in the atmospheric pressure. The composition of the air in the shaft may change very quickly—it may be normal in the morning, but be deficient in oxygen by the afternoon.
Prevention of exposure to dust should in the first place be implemented by technical means, such as wet drilling (and/or drilling with LEV), wetting of the material before it is pulled down and loaded to the transport, LEV of mining machines and mechanical ventilation of tunnels. Technical control measures may not be sufficient to lower the concentration of respirable dust to an acceptable level in some technological operations (e.g., during drilling and sometimes also in the case of wet drilling), and therefore it may be necessary to supplement the protection of the workers engaged in such operations by the use of respirators.
The efficiency of technical control measures must be checked by monitoring the concentration of airborne dust. In the case of fibrogenic dust, it is necessary to arrange the programme of monitoring in such a way that it allows the registration of the exposure of individual workers. The individual exposure data, in connection with data about each worker’s health, are necessary for the assessment of the risk of pneumoconiosis in particular work conditions, as well as for the assessment of the efficiency of control measures in the long-run. Last but not least, the individual registration of exposure is necessary for evaluating the ability of individual workers to continue in their jobs.
Due to the nature of underground work, protection against noise depends mostly on the personal protection of hearing. Effective protection against vibrations, on the other hand, can be achieved only by eliminating or decreasing the vibration by mechanization of risky operations. PPE is not effective. Similarly, the risk of diseases due to physical overload of the upper extremities can be lowered only by mechanization.
Exposure to chemical substances can be influenced by the selection of appropriate technology (e.g., the use of formaldehyde resins and formamide should be eliminated), by good maintenance (e.g., of diesel engines) and by adequate ventilation. Organization and work regime precautions are sometimes very effective, especially in the case of the prevention of dermatoses.
Work in underground spaces in which the composition of the air is not known demands strict adherence to safety rules. Entering such spaces without isolating breathing apparatuses must not be allowed. The work should be done only by a group of at least three people—one worker in the underground space, with breathing apparatus and safety harness, the others outside with a rope to secure the inside worker. In case of accident it is necessary to act quickly. Many lives have been lost in efforts to save the victim of an accident when the safety of the rescuer was disregarded.
Pre-placement, periodic and post-employment preventive medical examinations are a necessary part of the health and safety precautions for workers in tunnels. The frequency of periodic examinations and the type and scope of special examinations (x ray, lung functions, audiometry and so on) should be individually determined for each workplace and for each job according to the working conditions.
Prior to groundbreaking for underground work, the site should be inspected and soil samples should be taken in order to plan the excavation. Once work is underway, the work site should be inspected daily to prevent roof falls or cave-ins. The workplace of solitary workers should be inspected at least twice each shift. Fire suppression equipment should be strategically placed throughout the underground work site.
The construction industry forms 5 to 15% of the national economy of most countries and is usually one of the three industries having the highest rate of work-related injury risks. The following chronic occupational health risks are pervasive (Commission of the European Communities 1993):
Preventive health services for construction workers should be planned with these risks as priorities.
Types of Occupational Health Services
Occupational health services for construction workers consist of three main models:
Specialized services are the most effective but also the most expensive in terms of direct costs. Experiences from Sweden indicate that the lowest injury rates on construction sites worldwide and a very low risk for occupational diseases among construction workers are associated with extensive preventive work through specialized service systems. In the Swedish model, called Bygghälsan, technical and medical prevention have been combined. Bygghälsan operates through regional centres and mobile units. During the severe economic recession of the late 1980s, however, Bygghälsan severely cut back its health service activities.
In countries that have occupational health legislation, construction companies usually buy the needed health services from companies serving general industries. In such cases, the training of occupational health personnel is important. Without special knowledge of the circumstances surrounding construction, medical personnel cannot provide effective preventive occupational health programmes for construction companies.
Some large multinational companies have well-developed occupational safety and health programmes that are part of the culture of the enterprise. The cost-benefit calculations have proved these activities economically profitable. Nowadays, occupational safety programmes are included in quality management of most international companies.
Mobile health clinics
Because construction sites are often situated far from any established providers of health services, mobile health service units may be necessary. Practically all countries that have specialized occupational health services for construction workers use mobile units for delivering the services. The mobile unit’s advantage is the saving of work time by bringing the services to worksites. Mobile health centres are contained in a specially equipped bus or trailer and are especially suitable for all types of screening procedures, such as periodic health examinations. Mobile services should be careful to arrange in advance for collaboration with local providers of health services in order to secure follow-up evaluation and treatment for workers whose test results suggest a health problem.
Standard equipment for a mobile unit includes a basic laboratory with a spirometer and an audiometer, an interview room and x-ray equipment, when needed. It is best to design module units as multipurpose spaces so they can be used for different types of projects. The Finnish experience indicates that mobile units are also suitable for epidemiological studies, which can be incorporated into occupational health programmes, if properly planned in advance.
Contents of preventive occupational health services
Identification of risk at construction sites should guide medical activity, although this is secondary to prevention through proper design, engineering and work organization. Risk identification requires a multidisciplinary approach; this requires close collaboration between the occupational health personnel and the enterprise. A systematic workplace survey of risks using standardized checklists is one option.
Preplacement and periodic health examinations are usually conducted according to requirements set by legislation or guidance provided by authorities. The examination’s content depends on the exposure history of each worker. Short work contracts and frequent turnover of the construction workforce can result in “missed” or “inappropriate” health examinations, a failure to follow up on findings or unwarranted duplication of health examinations. Therefore, regular standard periodic examinations are recommended for all workers. A standard health examination should contain: an exposure history; symptom and illness histories with special emphasis on musculoskeletal and allergic diseases; a basic physical examination; and audiometry, vision, spirometry and blood pressure tests. The examinations should also provide health education and information on how to avoid occupational risks known to be common.
Surveillance and Prevention of Key Construction-related Problems
Musculoskeletal disorders and their prevention
Musculoskeletal disorders have multiple origins. Lifestyle, hereditary susceptibility and ageing, combined with improper physical strain and minor injuries, are commonly accepted risk factors for musculoskeletal disorders. The types of musculoskeletal problems have different exposure patterns in different construction professions.
There is no reliable test to predict an individual’s risk for acquiring a musculoskeletal disorder. Medical prevention of musculoskeletal disorders is based on guidance in ergonomic matters and lifestyles. Preplacement and periodic examinations can be used for this purpose. Non-specific strength testing and routine x rays of the skeletal system have no specific value for prevention. Instead, early detection of symptoms and a detailed work history of musculoskeletal symptoms can be used as a basis for medical counselling. A programme that performs periodic symptom surveys to identify work factors that can be changed has been shown to be effective.
Often, workers who have been exposed to heavy physical loads or strain think the work keeps them fit. Several studies have proved that this is not the case. Therefore, it is important that, in the context of health examinations, the examinees be informed about proper ways to maintain their physical fitness. Smoking has also been associated with lumbar disk degeneration and low-back pain. Therefore, anti-smoking information and therapy should be included in the periodic health examinations, too (Workplace Hazard and Tobacco Education Project 1993).
Occupational noise-induced hearing loss
The prevalence of noise-induced hearing loss varies among construction occupations, depending on levels and duration of exposure. In 1974, less than 20% of Swedish construction workers at age 41 had normal hearing in both ears. Implementation of a comprehensive hearing conservation programme increased the proportion in that age group having normal hearing to almost 40% by the late 1980s. Statistics from British Columbia, Canada, show that construction workers generally suffer significant loss of hearing after working more than 15 years in the trades (Schneider et al. 1995). Some factors are thought to increase susceptibility to occupational hearing loss (e.g., diabetic neuropathy, hypercholesterolemia and exposure to certain ototoxic solvents). Whole-body vibration and smoking may have an additive effect.
A large-scale programme for hearing conservation is advisable for the construction industry. This type of programme requires not only collaboration at the worksite level, but also supportive legislation. Hearing conservation programmes should be specific in work contracts.
Occupational hearing loss is reversible in the first 3 or 4 years after initial exposure. Early detection of hearing loss will provide opportunities for prevention. Regular testing is recommended to detect the earliest possible changes and to motivate workers to protect themselves. At the time of testing, the exposed workers should be educated in the principles of personal protection, as well as the maintenance and proper use of protection devices.
Occupational dermatitis is prevented mainly by hygienic measures. The proper handling of wet cement and skin protection are effective in promoting hygiene. During health examinations, it is important to stress the importance of avoiding skin contact with wet cement.
Occupational lung diseases
Asbestosis, silicosis, occupational asthma and occupational bronchitis can be found among construction workers, depending on their past work exposures (Finnish Institute of Occupational Health 1987).
There is no medical method to prevent the development of carcinomas after someone has been sufficiently exposed to asbestos. Regular chest x rays, every third year, are the most common recommendation for medical surveillance; there is some evidence that x-ray screening improves the outcome in lung cancer (Strauss, Gleanson and Sugarbaker 1995). Spirometry and anti-smoking information are usually included in the periodic health examination. Diagnostic tests for the early diagnosis of asbestos-related malignant tumours are not available.
Malignant tumours and other lung diseases related to asbestos exposure are widely underdiagnosed. Therefore, many construction workers eligible for compensation remain without benefits. In the late 1980s and early 1990s, Finland conducted a nationwide screening of workers exposed to asbestos. The screening revealed that only one-third of the workers with asbestos-related diseases and who had access to occupational health services had been diagnosed earlier (Finnish Institute of Occupational Health 1994).
Special needs of migrant workers
Depending on the construction site, the social context, sanitary conditions and climate may present important risks to construction workers. Migrant workers often suffer from psychosocial problems. They have a higher risk of work-related injuries than native workers. Their risk of carrying infectious diseases, such as HIV/AIDS, tuberculosis, and parasitic diseases must be taken into account. Malaria and other tropical diseases are problems for workers in areas where they are endemic.
In many large construction projects, a foreign workforce is used. A preplacement medical examination should be conducted in the home country. Also, the spreading of contagious diseases must be prevented through proper vaccination programmes. In the host countries, proper vocational training, health and safety education, and housing should be organized. Migrant workers should be provided the same access to health care and social security as native workers (El Batawi 1992).
In addition to preventing construction-related ailments, the health practitioner should work to promote positive changes in lifestyle, which can improve a worker’s health overall. Avoiding alcohol and smoking are the most important and fruitful themes for health promotion for construction workers. It has been estimated that a smoker costs the employer 20 to 30% more than a non-smoking worker. Investments in anti-smoking campaigns pay not only in the short term, with lower accident risks and shorter sick leaves, but also in the long term, with lower risks of cardiovascular pulmonary diseases and cancer. In addition, tobacco smoke has harmful multiplier effects with most dusts, especially with asbestos.
It is difficult to prove any direct economic benefit of occupational health services to an individual construction company, especially if the company is small. Indirect cost-benefit calculations show, however, that accident prevention and health promotion are economically beneficial. Cost-benefit calculations of investments in preventive programmes are available for companies to use internally. (For a model used extensively in Scandinavia, see Oxenburg 1991.)
Implementation of the EC directive Minimum Regulations for Health and Safety on Temporary and Mobile Building Sites typifies the legal regulations emanating from the Netherlands and from the European Union. Their aim is to improve working conditions, to combat disability and to reduce sickness absenteeism. In the Netherlands, these regulations for the construction industry are expressed in the Arbouw Resolution, Chapter 2, Section 5.
As is often the case, the legislation seems to be following the social changes that began in 1986, when organizations of employers and employees joined to establish the Arbouw Foundation to provide services for construction companies in civil engineering and utility construction, earth works, roadbuilding and water construction and the completion sectors of the industry. Thus, the new regulations are scarcely a problem for the responsible companies already committed to implement health and safety considerations. The fact that these principles are often very difficult to put into practice, however, has led to non-observance and unfair competition and, consequently, the need for legal regulations.
The legal regulations focus on preventive measures before the construction project is started and while it is in progress. This will yield the greatest long-term benefit.
The Health and Safety Act stipulates that evaluations of risks must address not only those arising from materials, preparations, tools, equipment and so on, but also those involving special groups of workers (e.g., pregnant women, young and elderly workers and those with disabilities).
Employers are obliged to have written risk evaluations and inventories produced by certified experts, who may be employees or external contractors. The document must include recommendations for eliminating or limiting the risks and must also stipulate phases of the work when qualified specialists will be required. Some construction companies have developed their own approach to the evaluation, the General Business Investigation and Risk Inventory and Evaluation (ABRIE), which has become the prototype for the industry.
The Health and Safety Act obliges employers to offer a periodic health examination to their employees. The purpose is to identify health problems that may make certain jobs especially hazardous for some workers unless certain precautions are taken. This requirement echoes the various collective labour agreements in the construction industry which for years have required employers to provide employees with comprehensive occupational health care, including periodic medical examinations. The Arbouw Foundation has contracted with the Federation of Occupational Health and Safety Care Centres for the provision of these services. Over the years, a wealth of valuable information has been accumulated which has contributed to enhancement of the quality of the risk inventories and evaluations.
The Health and Safety Act also requires employers to have an absenteeism policy which includes a stipulation that experts in this field be retained to monitor and counsel disabled employees.
Many health and safety risks can be traced to inadequacies in the building and organization choices or to poor planning of the work when setting up a project. To obviate this, the employers, employees and the government agreed in 1989 on a working conditions covenant. Among other things, it specified cooperation between clients and contractors and between contractors and subcontractors. This has resulted in a code of conduct which serves as a model for the implementation of the European directive on temporary and mobile building sites.
As part of the covenant, Arbouw formulated limits for exposure to hazardous substances and materials, along with guidelines for the application in various construction operations.
Under the leadership of Arbouw, the FNV Building Workers and Wood Workers Union, the FNV Industry Union and the Mineral Wool Association, Benelux, agreed to a contract that called for the development of glass wool and mineral wool products with less dust emission, development of the safest possible production methods for glass wool and mineral wool, formulation and promotion of working methods for the safest use of these products and performance of the research necessary to establish safe exposure limits to them. The exposure limit for respirable fibres was set at 2/cm3 although a limit of 1/cm3 was regarded as feasible. They also agreed to eliminate the use of raw and secondary materials that are health risks, using as criteria the exposure limits formulated by Arbouw. Performance under this agreement will be monitored until it expires on 1 January 1999.
Construction Process Quality
The implementation of the EC directive does not stand in isolation but is an integral part of company health and safety policies, along with quality and environmental policies. Health and safety policy is critical part of the quality policy of the companies. The laws and regulations will be enforceable only if the employers and employees of the construction industry have played a role in their development. The government has dictated the development of a model health and safety plan that is practicable and can be enforced to prevent unfair competition from companies that ignore or subvert it.
Diversity of Projects and Work Activities
Many people outside the construction industry are unaware of the diversity and degree of specialization of work undertaken by the industry, though they see portions of it every day. In addition to traffic delays caused by encroachments on roads and street excavations, the public is frequently exposed to buildings being erected, subdivisions being constructed and, occasionally, to the demolition of structures. What is hidden away from view, in most cases, is the large amount of specialized work done either as part of a “new” construction project or as part of the ongoing repairs maintenance associated with almost anything constructed in the past.
The list of activities is very diverse, ranging from electrical, plumbing, heating and ventilating, painting, roofing and flooring work to very specialized work such as installing or repairing overhead doors, setting heavy machinery, applying fireproofing, refrigeration work and installing or testing communications systems.
Table 1. Value of construction projects in Canada, 1993 (based on value of building permits issued in 1993).
Type of project
Value ($ Cdn)
% of total
Residential buildings (houses, apartments)
Industrial buildings (factories, mining plants)
Commercial buildings (offices, stores, shops etc.)
Institutional buildings (schools, hospitals)
Other buildings (airports, bus stations, farm buildings, etc.)
Marine facilities (wharves,dredging)
Roads and highways
Water and sewage systems
Dams and irrigation
Electric power (thermal/nuclear/hydro)
Railway, telephone and telegraph
Gas and oil (refineries, pipelines)
Other engineering construction (bridges, tunnels, etc.)
Source: Statistics Canada 1993.
The health and safety aspects of the work depend in large measure on the nature of the project. Each type of project and each work activity presents different hazards and solutions. Often, the severity, scope or size of the problem is related to the size of the project as well.
Clients are the individuals, partnerships, corporations or public authorities for whom construction is carried out. The vast majority of construction is done under contractual arrangements between clients and contractors. A client may select a contractor based on past performance or through an agent such as an architect or engineer. In other cases, it may decide to offer the project through advertising and tendering. The methods used and the client’s own attitude to health and safety can have a profound effect on the project’s health and safety performance.
For example, if a client chooses to “pre-qualify” contractors to ensure that they meet certain criteria, then this process excludes inexperienced contractors, those who may not have had satisfactory performance and those without qualified personnel required for the project. While health and safety performance has not previously been one of the common qualifications sought or considered by clients, it is gaining in usage, primarily with large industrial clients and with government agencies that purchase construction services.
Some clients promote safety much more than others. In some cases, this is due to the risk of damage to their existing facilities when contractors are brought in to perform maintenance or to expand the client’s facilities. Petrochemical companies in particular make it clear that contractor safety performance is a key condition of the contract.
Conversely, those firms who choose to offer their project through an unqualified open bidding process to obtain the lowest price often end up with contractors that may be unqualified to perform the work or who take short cuts to save on time and materials. This can have an adverse effect on health and safety performance.
Many people who are not familiar with the nature of the contractual arrangements common in construction presume that one contractor performs all or at least the major part of most building construction. For example, if a new office tower, sports complex or other high-visibility project is being constructed, the general contractor usually erects signs and often company flags to indicate its presence and to create the impression that this is “its project”. Years ago, this impression may have been relatively accurate, since some general contractors actually undertook to perform substantial parts of the project with their own direct-hire forces. However, since the mid-1970s, many, if not most, general contractors have assumed more of a project management role on large projects, with the vast majority of the work contracted out to a network of subcontractors, each of which has special skills in a particular aspect of the project. (See table 2)
Table 2. Contractors/subcontractors on typical industrial/commercial/institutional projects
The influence that this network of contractors may have on health and safety becomes fairly obvious when it is compared with a fixed worksite such as a factory or a mill. At a typical fixed-industry workplace, there is only one management entity, the employer. The employer has sole responsibility for the workplace, the lines of command and communication are simple and direct, and only one corporate philosophy applies. At a construction project, there may be ten or more employer entities (representing the general contractor and the usual subcontractors), and the lines of communication and authority tend to be more complex, indirect and often confused.
The attention given to health and safety by the person or company in charge can influence the health and safety performance of others. If the general contractor has attached a high degree of importance to health and safety, this can have a positive influence on the health and safety performance of the subcontractors on the project. The converse is also true.
Additionally, the overall health and safety performance of the site can be adversely affected by the performance of one subcontractor (e.g., if one subcontractor has poor housekeeping, leaving a mess behind as his or her forces move through the project, it can create problems for all of the other subcontractors onsite).
Regulatory efforts regarding health and safety are generally more difficult to introduce and administer in these multi-employer workplaces. It may be difficult to determine which employer has responsibility for which hazards or solutions, and any administrative controls which appear to be eminently workable in a single-employer workplace may need significant modification to be workable on a multi-employer construction project. For example, information regarding hazardous materials used on a construction project must be communicated to those who work with or near the materials, and workers must be adequately trained. At a fixed workplace with only one employer, all of the material and the information accompanying it is much more readily obtained, controlled and communicated, whereas on a construction project, any of the various subcontractors may be bringing in hazardous materials of which the general contractor has no knowledge. Additionally, workers employed by one subcontractor using a certain material may have been trained, but the crew working for another subcontractor in the same area but doing something entirely different may know nothing about the material and yet could be as much at risk as those using the material directly.
Another factor which emerges regarding contractor-contractor relationships relates to the bidding process. A subcontractor who bids too low may take short-cuts that compromise health and safety. In these cases, the general contractor must ensure that subcontractors adhere to the standards, specifications and statutes pertaining to health and safety. It is not uncommon on projects where everyone has bid very low to observe continuing health and safety problems coupled with excessive passing of responsibility, until regulatory authorities step in to impose a solution.
A further problem relates to the scheduling of work and the impact this can have on health and safety. With several different subcontractors on the site at one time, competing interests may create problems. Each contractor wants to get his or her work done as quickly as possible. When two or more contractors want to occupy the same space, or when one has to perform work overhead of another, problems can occur. This is typically a much more common problem in construction than in fixed industry, where the main competing interests tend to involve only operations versus maintenance.
The several employers on a particular project may have somewhat different relationships with their employees than those common at most fixed industrial workplaces. For example, unionized workers at a manufacturing facility tend to belong to one union. When the employer needs additional workers, it interviews and hires them and the new employees join the union. Where there are former unionized workers on layoff, they are re-hired generally on a seniority basis.
In the unionized part of the construction industry, a completely different system is used. Employers form collective associations which then enter into agreements with building and construction trade unions. The majority of the non-salaried direct-hire employees in the industry work through their union. When, for example, a contractor needs five additional carpenters at a project, he or she would call the local Carpenters’ Union and place a request for five carpenters to show up for work at the project on a certain day. The union would notify the five members at the top of the employment list that they are to report to the project to work for the particular firm. Depending on the provisions of the collective agreement between the employers and the union, the contractor may be able to “name hire” or select some of these workers. If there are no union members available to fill the employment call, the employer may be able to hire temporary workers who would join the union, or the union may bring in skilled workers from other locals to help fill the demand.
In non-unionized situations, employers use different processes to obtain additional staff. Prior employment lists, local employment centres, word of mouth and advertising in local newspapers are the principal methods used.
It is not uncommon for workers to be employed by several different employers in the course of a year. The employment duration varies with the nature of the project and the amount of work to be done. This places a large administrative load on the construction contractors compared with their fixed-industry counterparts (e.g., recordkeeping for income taxes, workers’ compensation, unemployment insurance, union dues, pensions, licensing and other regulatory or contractual issues).
This situation presents some unique challenges compared to the typical fixed-industry workplace. Training and qualifications must not only be standardized but portable from one job or sector to another. These important issues affect the construction industry much more profoundly than fixed industries. Construction employers expect workers to come to the project with certain skills and capabilities. In most trades, this is accomplished by a comprehensive apprenticeship programme. If a contractor places a call for five carpenters, he or she expects to see five qualified carpenters at the project on the day they are needed. If health and safety regulations require special training, the employer needs to be able to access a pool of workers with this training, since the training may not be readily available at the time the work is scheduled to start. An example of this is the Certified Worker Programme required at larger construction projects in Ontario, Canada, which involves having joint health and safety committees. Since this training is not currently part of the apprenticeship programme, alternative training systems had to be put in place to create a pool of trained workers.
With growing emphasis on specialized training or at least confirmation of skill level, training programmes conducted in conjunction with the building and construction trades unions will likely grow in importance, number and variety.
The structure of organized labour mirrors the way in which contractors have specialized within the industry. On a typical construction project, five or more trades may be represented onsite at any one time. This involves many of the same problems posed by multiple employers. Not only are there competing interests to deal with, but lines of authority and communication are more complex and sometimes blurred when compared with a single-employer, single-union workplace. This influences many aspects of health and safety. For example, which worker from which union will represent all workers on the project if there is a regulatory requirement for a health and safety representative? Who gets trained in what and by whom?
In the case of rehabilitation and reinstatement of injured workers, the options for skilled construction workers are much more limited than those of their fixed-industry counterparts. For example, an injured worker at a factory may be able to return to some other job at that workplace without crossing important jurisdictional boundaries between one union and another, because there is typically only one union in the factory. In construction, each trade has fairly clearly defined jurisdiction over the types of work its members can perform. This greatly limits the options for injured workers who may not be able to perform their normal pre-injury job functions but could none the less perform some other related work at that workplace.
Occasionally, jurisdictional disputes arise over which union should perform certain types of work which have health and safety implications. Examples include scaffold erection, boom truck operation, asbestos removal and rigging. Regulations in these areas need to consider jurisdictional concerns, especially with respect to licensing and training.
The Dynamic Nature of Construction
Construction workplaces are in many respects quite different from fixed industry. Not only are they different, they tend to be constantly changing. Unlike a factory which operates at a given location day after day, with the same equipment, the same workers, the same processes and generally the same conditions, construction projects evolve and change from day to day. Walls are erected, new workers from different trades arrive, materials change, employers change as they complete their portions of the work, and most projects are affected to some degree just by the changes in the weather.
When one project is completed, workers and employers move on to other projects to start all over again. This indicates the dynamic nature of the industry. Some employers work in several different cities, provinces, states or even countries. Similarly, many skilled construction workers move with the work. These factors influence many aspects of health and safety, including workers’ compensation, health and safety regulations, performance measurement and training.
The construction industry is presented with some very different conditions from those in fixed industry. These conditions must be considered when control strategies are being contemplated and may help to explain why things are done differently in the construction industry. Solutions developed with the input from both construction labour and construction management, who know these conditions and how to deal effectively with them, offer the best chance for improving health and safety performance.
Improving Occupational Health and Safety
Construction companies are increasingly adopting the quality management systems spelled out by the International Organization for Standardization (ISO), such as the ISO 9000 series and the subsequent regulations that have been based on it. Although no recommendations on occupational health and safety are specified in this set of standards, there are cogent reasons for including preventive measures when implementing a management system such as that required by the ISO 9000.
Occupational health and safety regulations are written and implemented and are continuously being adapted to technological progress as well as to new safety techniques and to advances in occupational medicine. All too often, however, they are not followed, either deliberately or out of ignorance. When this occurs, models for safety management, such as the ISO 9000 series, assist in integrating the structure and content of preventive measures into management. The advantages of such a comprehensive approach are obvious.
Integrated management means that occupational health and safety regulations are no longer looked at in isolation, but gain relevance from the corresponding sections of a quality management handbook, as well as in process and work instructions, thus creating a fully integrated system. This integral approach can improve the chances of greater attention to accident prevention measures in daily construction practice and, thereby, reduce the number of workplace accidents and injuries. Dissemination of a handbook that integrates occupational health and safety procedures into the processes it describes is crucial for this process.
New management methods are aimed at putting people closer to the centre of the processes. Co-workers are being more actively involved. Information, communication and cooperation are promoted across hierarchical barriers. The reduction of absences due to illness or workplace accidents enhances the implementation of the principles of quality management in construction.
With the development of new building methods and equipment, safety requirements increase steadily in number. The increasing concern with environmental protection makes the problem even more complex. Coping with the demands of modern prevention is difficult without appropriate regulations and a centrally directed articulation of the process and work instructions. Clear divisions of responsibility and effective coordination for the prevention plan should, therefore, be written into the quality management system.
Documentation of the existence of an occupational safety management system is increasingly required when contractors submit bids for work, and its effectiveness has become one of the criteria for awarding a contract.
The pressure of international competition could become even greater in the future. It seems prudent, therefore, to integrate preventive measures into the quality management system now, rather than waiting and being forced by increasing competitive pressure to do so later, when the pressure of time and the costs of personnel and financing will be much greater. Furthermore, a not inconsiderable benefit of an integrated prevention/quality management system is that having such a well-documented programme in place is likely to reduce the costs of coverage, not only for workers’ compensation, but also for product liability.
Company management must be committed to the integration of occupational health and safety into the management system. Goals specifying the content and time-frame of this effort should be defined and included in the basic statement of company policy. The necessary resources should be made available and appropriate personnel assigned to accomplish the project goals. Specialized safety personnel are generally required in large and mid-sized construction companies. In smaller companies, the employer must take the responsibility for the preventive aspects of the quality management system.
A periodic company management review closes the circle. The collective experiences in utilizing the integrated prevention/ quality management system should be examined and assessed, and plans for revision and for subsequent review should be formulated by company management.
Assessment of results of the occupational safety management system that has been instituted is the second step in the integration of preventive measures and quality management.
The dates, kinds, frequency, causes and costs of accidents should be compiled, analysed and shared with all those in the company with relevant responsibilities. Such an analysis enables the company to set priorities in formulating or modifying process and work instructions. It also makes clear the extent to which occupational health and safety experience affects all divisions and all processes in the construction company. For this reason, defining the interface between company processes and preventive aspects takes on great importance. During bid preparation, the resources in time and money needed for comprehensive preventive measures, such as those incurred in clearing debris, can be precisely calculated.
When purchasing construction materials, attention should be paid to the availability of substitutes for potentially dangerous materials. From the beginning of a project responsibility for occupational health and safety should be assigned for particular aspects and each phase of the construction project. The need and availability for special training in occupational health and safety as well as the relative risks of injury and disease should be compelling considerations in the adoption of particular construction processes. These conditions must be recognized early on so that appropriately qualified workers can be selected and the courses of instruction can be arranged in a timely manner.
The responsibilities and authorities of the personnel assigned to safety and how they fit into the daily work should be documented in writing and collated with the onsite task descriptions. The construction company’s occupational safety staff should appear shown in its organizational chart, which, along with a clear responsibility matrix and schematic flow-charts of processes, should appear in the quality management handbook.
An Example from Germany
In practice, there are four formal procedures and their combinations for integrating occupational health and safety into a quality management system that have been implemented in Germany:
Integration in Quality Management
Once the assessment is completed, at the latest, those responsible for the construction project should contact the quality management officers and decide on the steps for actually integrating occupational safety into the management system. Comprehensive preparatory work should facilitate setting common priorities during the work that promise the greatest preventive results.
The demands of prevention that come out of the assessment are first divided into those that can be categorized according to the processes specific to the company and those that should be considered separately since they are more widespread, more comprehensive or of such a special character that they demand separate consideration. The following question can be of assistance in this categorization: Where would the interested reader of the handbook (e.g., the “customer” or the worker) most likely look for the relevant preventive policy, the section of a chapter devoted to a process specific to the company, or in a special section on occupational health and safety? Thus, it appears, a specialized procedural instruction on transporting hazardous materials would make the most sense in almost all construction companies if it were included in section on handling, storing, packing, conserving and shipping.
Coordination and Implementation
After this formal categorization should come linguistic coordination to ensure easy readability (this means presentation in the appropriate language(s) and in terms easily understood by individuals with educational levels characteristic of the particular workforce). Finally, the final documents must be formally endorsed by the top management of the company. At this juncture, it would be useful to publicize the significance of the changed or newly-implemented procedures and work instructions in company bulletins, safety circles, memos and any other available media, and to promote their application.
To assess the effectiveness of the instructions, appropriate questions may be prepared for inclusion into general audits. In this manner, the coherence of work processes and occupational health and safety considerations is made unmistakably clear to the worker. Experience has shown that workers may at first be surprised when an audit team on the construction site in their particular division routinely asks questions on accident prevention as a matter of course. The consequent increase in the attention paid to safety and health by the workforce confirms the value of the integration of prevention into the quality management programme.
The term construction industry is used worldwide to cover what is a collection of industries with very different practices, brought together temporarily on the site of a building or civil engineering job. The scale of operations ranges from a single worker carrying out a job lasting minutes only (e.g., replacing a roof tile with equipment consisting of a hammer and nails and possibly a ladder) to vast building and civil engineering projects lasting many years that involve hundreds of different contractors, each with their own expertise, plant and equipment. However, despite the enormous variation in scale and complexity of operations, the major sectors of the construction industry have a great deal in common. There is always a client (known sometimes as the owner) and a contractor; except for the very smallest jobs, there will be a designer, either an architect or engineer, and if the project involves a range of skills, it will inevitably require additional contractors working as subcontractors to the main contractor (see also the article “Organizational factors affecting health and safety” in this chapter). While small-scale domestic or agricultural buildings may be built on the basis of an informal agreement between the client and builder, the vast majority of building and civil engineering work will be carried out under the terms of a formal contract between the client and contractor. This contract will set out details of the structure or other work that the contractor is to provide, the date by which it is to be built and the price. Contracts may contain a great deal besides the job, the time and the price, but those are the essentials.
The two broad categories of construction projects are building and civil engineering. Building applies to projects involving houses, offices, shops, factories, schools, hospitals, power and railway stations, churches and so on—all those kinds of structures that in everyday speech we describe as “buildings”. Civil engineering applies to all the other built structures in our environment, including roads, tunnels, bridges, railways, dams, canals and docks. There are structures that appear to fall into both categories; an airport involves extensive buildings as well as civil engineering in the creation of the airfield proper; a dock may involve warehouse buildings as well excavation of the dock and raising of the dock walls.
Whatever the type of structure, building and civil engineering both involve certain processes such as building or erection of the structure, its commissioning, maintenance, repair, alteration and ultimately its demolition. This cycle of processes occurs regardless of the type of structure.
Small Contractors and the Self-employed
While there are variations from country to country, construction is typically an industry of small employers. As many as 70 to 80% of contractors employ less than 20 workers. This is because many contractors start out as a single tradesperson working alone on small-scale jobs, probably domestic ones. As their business expands, such tradespeople start to employ a few workers themselves. The workload in construction is rarely consistent or predictable, as some jobs finish and others start up at different times. There is a need in the industry to be able to move groups of workers with particular skills from job to job as the work requires. Small contractors fulfil this role.
Alongside the small contractors there is a population of self-employed workers. Like agriculture, construction has a very high proportion of self-employed workers. These again are usually tradespeople, such as carpenters, painters, electricians, plumbers and bricklayers. They are able to find a place in either small-scale domestic work or as part of the workforce on bigger jobs. In the boom construction period of the late 1980s, there was an increase in workers claiming to be self-employed. This was partly because of tax incentives for the individuals concerned and use by contractors of so-called self-employed who were cheaper than employees. Contractors were not faced with the same level of social security costs, were not required to train self-employed persons and could get rid of them more easily at the end of jobs.
The presence in construction of so many small contractors and self-employed individuals tends to militate against effective management of health and safety for the job as a whole and, with such a transitory workforce, certainly makes it more difficult to provide proper safety training. Analysis of fatal accidents in the United Kingdom over a 3-year period showed that about half the fatal accidents happened to workers who had been onsite for a week or less. The first few days on any site are especially hazardous to construction workers because, however experienced they may be as tradespeople, each site is a unique experience.
Public and Private Sectors
Contractors may be part of the public sector (e.g., the works department of a city or district council) or they are part of the private sector. A considerable amount of maintenance used to be done by such public works departments, especially on housing, schools and roads. Recently there has been a move to encourage greater competition in such work, partly as a result of pressures for better value for money. This has led firstly to a reduction in the size of public works departments, even their total disappearance in some places, and to the introduction of mandatory competitive tendering. Jobs previously done by public works departments are now done by private-sector contractors under severe “lowest tender wins” conditions. In their need to cut costs, contractors may be tempted to reduce what are seen as overheads such as safety and training.
The distinction between public and private sectors may also apply to clients. Central and local government (along with transportation and public utilities if under the control of central or local government) may all be clients for construction. As such they would generally be thought to be in the public sector. Transportation and utilities run by corporations would usually be considered to be in the private sector. Whether a client is in the public sector sometimes influences attitudes towards inclusion of some items of safety or training in the cost of construction work. Recently public- and private-sector clients have been under similar constraints as regards competitive tendering.
Work across National Boundaries
An aspect of public-sector contracts of increasing importance is the need for tenders to be invited from beyond national boundaries. In the European Union, for example, large-scale contracts beyond a value set out in Directives, must be advertised within the Union so that contractors from all member countries may tender. The effect of this is to encourage contractors to work across national boundaries. They are then required to work in accordance with the local national health and safety laws. One of the aims of the European Union is to harmonize standards between member states in health and safety laws and their application. Major contractors working in parts of the world subject to similar regimes must therefore be familiar with health and safety standards in those countries where they carry out work.
In buildings, the designer is usually an architect, although on small-scale domestic housing, contractors sometime provide such design expertise as is necessary. If the building is large or complex, there may be architects dealing with design of the overall scheme as well as structural engineers concerned with design of, for example, the frame, and specialist engineers involved with design of the services. The architect for the building will ensure that sufficient space is provided in the right places in the structure to permit installation of plant and services. Specialist designers will be concerned to ensure that the plant and services are designed to operate to the required standard when installed in the structure in the places provided by the architect.
In civil engineering, the lead in design is more likely to be taken by a civil or structural engineer, although in high-profile jobs where visual impact may be an important factor, an architect may have an important role in the design team. In tunnelling, railways and highways, the lead in design is likely to be taken by structural or civil engineers.
The role of the developer is to seek to improve the utilization of land or buildings and profit from that improvement. Some developers simply sell the improved land or buildings and have no further interest; others may retain ownership of land or even buildings and reap a continuing interest in the form of rents that are greater than before the improvements.
The skill of the developer is to identify sites either as empty land or under-utilized and out-of-date buildings where application of construction skills will improve their value. The developer may use his or her own finances, but perhaps more often exercises further skills in identifying and bringing together other sources of finance. Developers are not a modern phenomenon; the expansion of cities over the last 200 years owes a great deal to developers. Developers may themselves be clients for the construction work, or they may simply act as agents for other parties who provide finance.
Types of Contract
In the traditional contract, the client arranges for a designer to prepare a full design and specifications. Contractors are then invited by the client to tender or bid for doing the job in accordance with the design. The role of the contractor is largely confined to construction proper. The contractor’s involvement in questions of design or specification is then mainly a matter of seeking such changes as will make it easier or more efficient to build—to improve “buildability”.
The other common arrangement in construction is the design and build contract. The client requires a building (perhaps an office block or shopping development) but has no firm ideas on detailed aspects of its design other than the size of site, number of persons to be accommodated or scale of activities to be carried out in it. The client then invites tenders from either designers or contractors to submit both design and construction proposals. Contractors working in design and build either have their own design organization or have close links with an external designer who will work for them on the job. Design and build may involve two stages in design: an initial stage where a designer prepares an outline scheme which is then put out to tender; and a second stage where the successful design and build contractor will then carry out further design on detailed aspects of the job.
Maintenance and emergency contracts cover a wide variety of arrangements between clients and contractors and represent a significant proportion of the work of the construction industry. They generally run for a fixed period, require the contractor to do certain types of work or to work on a “call-off” basis (i.e., work that the client calls the contractor in to do). Emergency contracts are widely used by public authorities who are responsible for providing a public service that ought not to be interrupted; government agencies, public utilities and transportation systems make wide use of them. Operators of factories, particularly those with continuous processes such as petrochemicals, also make wide use of emergency contracts to deal with problems in their facilities. Having entered such a contract, the contractor undertakes to make available suitable workers and plant to carry out the work, often at very short notice (e.g., in the case of emergency contracts). The advantage to the client is that he or she does not need to retain workers on payroll or have plant and equipment that may only occasionally be used to deal with maintenance and emergencies.
Pricing of maintenance and emergency contracts may be on the basis of a fixed sum per annum, or on the basis of time spent carrying out work, or some combination.
Perhaps the most common publicly known example of such contractors is maintenance of roads and emergency repairs to gas main or power supplies that have either failed or been accidentally damaged.
Whatever the form of contract, the same possibilities arise for clients and designers to influence the health and safety of contractors by decisions made in the early stage of the job. Design and build perhaps permits closer liaison between the designer and contractor on health and safety.
Price is always an element in a contract. It may simply be a single sum for the cost of doing the job, such as building a house. Even with a single lump sum, the client may have to pay part of the price in advance of the job starting, to enable the contractor to buy materials. The price may, however, be on a cost-plus basis, where the contractor is to recover his or her costs plus an agreed amount or percentage for profit. This arrangement tends to work to the disadvantage of the client, since there is no incentive for the contractor to keep costs down. The price may also have bonuses and penalties attached to it, so that the contractor will receive more money if, for example, the job is completed earlier than the agreed time. Whatever form the price takes for the job, it is usual for payments to be made in stages as the work progresses, either on completion of certain parts of the job by agreed dates or on the basis of some agreed method of measuring the work. At the end of construction proper, it is common for an agreed proportion of the price to be kept back by the clients until “snags” have been put right or the structure has been commissioned.
During the course of the job, the contractor may encounter problems that were not foreseen when the contract was made with the client. These might require changes to the design, the construction method or the materials. Usually such changes will create extra costs for the contractor, who then seeks to recover from the client on the basis that these items become agreed “variations” from the original contract. Sometimes recovery of the cost of variations can make the difference for the contractor between doing the job at a profit or loss.
The pricing of contracts can affect health and safety if inadequate provision is made in the contractor’s tender to cover the costs of providing safe access, lifting equipment and so on. This becomes even more difficult where, in an attempt to ensure that they obtain value for money from contractors, clients pursue a vigorous policy of competitive tendering. Governments and local authorities apply policies of competitive tendering to their own contracts, and indeed there may be laws requiring that contracts can be awarded only on the basis of competitive tendering. In such a climate, there is always a risk that the health and safety of construction workers will suffer. In cutting costs, clients may resist a reduction in the standard of construction materials and methods, but at the same time be totally unaware that in accepting the lowest tender, they have accepted working methods that are more likely to endanger construction workers. Even in a situation of competitive tendering, contractors submitting tenders should have to make clear to the client that their bid adequately covers the cost of health and safety involved in their proposals.
Developers can influence health and safety in construction in ways similar to clients, firstly by using contractors who are competent in health and safety and architects who take health and safety into account in their designs, and secondly in not automatically accepting the lowest tenders. Developers generally want to be associated only with successful developments, and one measure of success ought to be projects where there are no major health and safety problems during the construction process.
Building Standards and Planning
In the case of buildings, whether housing, commercial or industrial, projects are subject to planning laws that dictate where certain types of development may take place (e.g., that a factory may not be built among houses). Planning laws may be very specific about the appearance, materials and size of buildings. Typically areas identified as industrial zones are the only places where factory buildings may be erected.
Often there are also building regulations or similar standards that specify in precise detail many aspects of the design and specification of buildings—for example, the thickness of walls and timbers, depth of foundations, insulation characteristics, size of windows and rooms, layout of electrical wiring and earthing, layout of plumbing and pipework and many other issues. These standards have to be followed by clients, designers, specifiers and contractors. They limit their choices but at the same time ensure that buildings are built to an acceptable standard. Planning laws and building regulations thus affect the design of buildings and their cost.
Projects to build housing may consist of a single house or vast estates of individual houses or flats. The client may be each individual householder, who will then normally be responsible for maintenance of his or her own house. The contractor will usually remain responsible for correcting defects in construction for a period of months after building is finished. However, if the project is for many houses, the client may be a public body, either in local or national government, with responsibility for providing housing. There are also large private bodies like housing associations for whom numbers of houses may be built. Public or private bodies with responsibilities for providing housing generally rent the finished houses to occupants, retaining a greater or lesser degree of responsibility for maintenance also. Building projects involving blocks of flats usually have a client for the block as a whole, who then lets out individual flats under a leasing arrangement. In this situation the owner of the block has responsibility for carrying out maintenance but passes on the cost to the tenants. In some countries ownership of individual flats in a block can rest with the occupants of each flat. There has to be some arrangement, sometimes through an estate management contractor, whereby maintenance can be carried out and the necessary costs raised among the occupants.
Often houses are built on a speculative basis, by a developer. Specific clients or occupants of those houses may not have been identified at the outset but come on the scene after construction has begun and purchase or rent the property like any other article. Houses are usually fitted out with electrical, plumbing and drainage services and heating systems; a gas supply may also be laid on. Sometimes in an attempt to cut costs, houses are only partially finished, leaving it to the purchaser to install some of the fittings and to paint or decorate the building.
Commercial buildings include offices, factories, schools, hospitals, shops—an almost endless list of different types of buildings. In most cases these buildings are constructed for a particular client. However, offices and shops are often built on a speculative basis like housing, with the hope of attracting buyers or tenants. Some clients require an office or shop to be totally fitted out to their requirements, but very often the contract is for the structure and main services, with the client making arrangements to fit out the premises using specialist contractors in office and shop fitting.
Hospitals and schools are built for clients who have a clear idea of precisely what they want, and the clients often provide design input into the project. Plant and equipment in hospitals may cost more than the structure and involve a great deal of design that has to satisfy stringent medical standards. National or local government may also play a part in the design of schools by laying down very detailed requirements on space standards and equipment as part of its wider role in education. National governments usually have very detailed standards as to what is acceptable in hospital buildings and plant. Fitting out of hospitals and similarly complex buildings is a form of construction work usually carried out by specialist subcontractors. Such contractors not only require knowledge of health and safety in construction in general, but also need expertise in ensuring that their operations do not adversely affect the hospital’s own activities.
Industrial building or construction involves use of the mass- production techniques of manufacturing industry to produce parts of buildings. The ultimate example is the house brick, but normally the expression is applied to building using concrete parts or units that are assembled onsite. Industrial construction expanded rapidly after the Second World War to meet the demand for cheap housing, and it is more commonly found in mass housing developments. Under factory conditions it is possible to mass produce cast units that are consistently accurate in a way that would be virtually impossible under normal site conditions.
Sometimes units for industrial construction are manufactured away from the construction site in factories that may supply a wide area; sometimes, where the individual development is itself very large, a factory is set up onsite to serve that sole site.
Units designed for industrial construction must be structurally strong enough to stand up to being moved, lifted and lowered; they must incorporate anchorage points, or slots to permit safe attachment of lifting tackle, and must also include appropriate lugs or recesses to permit the units to fit together both easily and strongly. Industrial construction demands plant for transporting and lifting units into position and space and arrangements to store units safely when delivered to site, so that units are not damaged and workers are not injured. This technique of building tends to produce visually unattractive buildings, but on a large scale it is cheap; a whole room can be assembled from six cast units with window and door openings in place.
Similar techniques are used to produce concrete units for civil engineering structures like elevated motorways and tunnel linings.
Some clients for industrial or commercial buildings containing extensive complex plant wish simply to walk into a facility that will be up and running from their first day in the premises. Laboratories are sometimes constructed and fitted out on this basis. Such an arrangement is a “turn-key” project, and here the contractor will ensure that all aspects of plant and services are fully operational before handing the project over. The job may be done under a design and build contract so that, in effect, the turn-key contractor deals with everything from design to commissioning.
Civil Engineering and Heavy Construction
The civil engineering of which the public is most aware is work on highways. Some highway work is the creation of new roads on virgin land, but much of it is the extension and repair of existing highways. Contracts for highway work are usually for state or local government agencies, but sometimes roads remain under the control of contractors for some years after completion, during which time they are permitted to charge tolls. If civil engineering structures are being financed by government, then both the design and actual construction will be subject to a high degree of supervision by officials on behalf of government. Contracts for construction of highways are usually let to contractors on the basis of a contractor being responsible for a section of so many kilometres of the highway. There will be a main contractor for each section; but highway construction involves a number of skills, and aspects of the job such as steel work, concrete, shuttering and surfacing may be subcontracted by the main contractor to specialist firms. Highway construction is also sometimes carried out under management contract arrangements, where a civil engineering consultancy will provide management for the job, with all the work being done by subcontractors. Such a management contractor may also have been involved in design of the highway.
Construction of highways requires the creation of a surface whose gradients are suitable for the sort of traffic that will use it. In a generally level terrain, creation of the foundation of the highway may involve earthmoving—that is, shifting soil from cuttings to create embankments, building bridges across rivers and driving tunnels through mountainsides where it is not possible to go round the obstruction. Where labour costs are higher, such operations are carried out using mechanically powered plant such as excavators, scrapers, loaders and lorries. Where labour costs are lower, these processes may be carried out manually by large numbers of workers using hand tools. Whatever the actual methods adopted, highway construction requires high standards of route surveying and planning of the job.
Highway maintenance frequently requires roads to remain in use whilst repairs or improvements are carried out in part of the road. There is thus a hazardous interface between traffic movement and construction operations which makes good planning and management of the job even more important. There are often national standards for signage and coning off of roadworks and requirements as to the amount of separation there should be between construction and traffic, which may be difficult to achieve in a confined area. Control of traffic approaching roadworks is usually the responsibility of the local police, but requires careful liaison between them and the contractors. Highway maintenance creates traffic hold-ups, and accordingly contractors are put under pressure to finish jobs quickly; sometimes there are bonuses for finishing early and penalties for finishing late. Financial pressures must not undermine safety on what is very dangerous work.
Surfacing of highways may involve concrete, stone or tarmacadam. This requires a substantial logistical train to ensure that the required quantities of surfacing materials are in place in the right condition to ensure that surfacing proceeds without interruption. Tarmacadam requires special purpose spreading plant that keeps the surfacing material plastic while spreading it. Where the job is re-surfacing, plant will be required including picks and breakers so that the existing surface is broken up and removed. A final finish is usually applied to the surfaces of highways involving use of heavy powered rollers.
Creation of cuttings and tunnels may require use of explosives and then arrangements to shift the muck displaced by the blasting. The sides of cuttings may require permanent supports to prevent landslides or falls of ground onto the finished road.
Elevated highways often require structures similar to bridges, especially if the elevated section passes through an urban area when space is limited. Elevated highways are often constructed from cast reinforced concrete sections that are either cast in situ or cast in a fabrication area and then shifted to the required position onsite. The work will require large-capacity lifting machinery to lift cast sections, shuttering and reinforcing.
Temporary support arrangements or “falsework” to support sections of either elevated highways or bridges while they are being cast in position need to be designed to take into account the uneven loads imposed by concrete as it is poured. Design of falsework is as important as design of the structure proper.
Bridges in remote areas may be simple constructions from timber. More commonly today bridges are from reinforced concrete or steel. They may also be clad in brickwork or stone. If the bridge is to span a considerable gap, whether above water or not, its design will require specialist designers. Using today’s materials, the strength of the bridge span or arch is not achieved by mass material, which would be simply too heavy, but by skilful design. The main contractor for a bridge building job is usually a major general civil-engineering contractor with management expertise and plant. However, specialist subcontractors may deal with major aspects of the job like erection of steel work to form the span or casting or placing cast sections of the span in place. If the bridge is over water, one or both abutments that support the ends of the bridge may themselves have to be constructed in water, involving piling, coffer dams, mass concrete or stone work. A new bridge may be part of a new highway system, and approach roads may have to be built, themselves possibly elevated.
Good design is especially important in bridge building, so that the structure is strong enough to withstand the loads imposed on it in use and to ensure that it will not require maintenance or repair too frequently. The appearance of a bridge is often a very important factor, and again good design can balance the conflicting demands of sound engineering and aesthetics. Provision of safe means of access for maintenance of bridges needs to be taken into account during design.
Tunnels are a specialized form of civil engineering. They vary in size from the Channel Tunnel, with over 100 km of bores from 6 to 8 m in diameter, to mini-tunnels whose bores are too small for workers to enter and which are created by machines launched from access shafts and controlled from the surface. In urban areas, tunnels may be the only way to provide or improve transport routes or to provide water and drainage facilities. The proposed route of the tunnel requires as detailed a survey as possible to confirm the kind of ground that the tunnel workings will be in and whether there will be groundwater. The nature of the ground, the presence of groundwater and the end use of the tunnel all influence the choice of tunnelling method.
If the ground is consistent, like the chalk-clay beneath the English Channel, then machine digging may be possible. If high groundwater pressures are not encountered during pre- construction survey, then it is usually unnecessary for the workings to be pressurized to keep out the water. If working in compressed air cannot be avoided, this adds considerably to costs because airlocks have to be provided, workers need to be allowed time to decompress, and access to workings for plant and materials may be made more difficult. A large tunnel for a road or railway in consistent non-hard-rock ground might be dug using a full-face tunnel-boring machine (TBM). This is really a train of different machines linked together and moving forward on rails under its own power. The front face is a circular cutting head that rotates and feeds spoil back through the TBM. Behind the cutting head are various sections of the TBM that place the segments of tunnel lining rings in position around the surface of the tunnel, grout behind the lining rings and, in a very confined space, provide all the machinery to handle and place ring segments (each weighing some tonnes), remove spoil, bring grout and extra segments forward and house electric motors and hydraulic pumps to power the cutting head and segment-placing mechanisms.
A tunnel in non-hard-rock ground which is not consistent enough to use a TBM, may be dug using equipment such as roadheaders that bite into the face of the heading. Spoil falling from the roadheader onto the tunnel floor are to be collected by diggers and removed by lorry. This technique permits digging of tunnels that are not circular in section. The ground in which such a tunnel is dug will not usually have sufficient strength for it to remain unlined; without some form of lining there might be falls from roof and walls. The tunnel may be lined by liquid concrete sprayed onto a steel mesh held in position by rock bolts (the “New Austrian tunnelling method”) or by cast concrete.
If the tunnel is in hard rock, the heading will be dug by means of blasting, using explosives placed into shot holes drilled into the rock face. The trick here is to use the minimum of blast to achieve a fall of rock in the position and sizes required, thereby making it easier to remove the spoil. On bigger jobs, multiple drills mounted on tracked bases will be used along with diggers and loaders to remove spoil. Hard rock tunnels are often simply trimmed to provide an even surface, but are not then further lined. If the rock surface remains friable with a risk of pieces falling, then a lining will be applied, usually some form of sprayed or cast concrete.
Whatever the method of construction adopted for the tunnel, the effective supply of tunnelling materials and removal of spoil are vital to the successful progress of the job. Large tunnelling jobs may require extensive narrow-gauge construction rail systems to provide logistical support.
Dams invariably contain large quantities of earth or rock to provide mass to resist the pressure from water behind them; some dams are also covered in masonry or reinforced concrete. Depending on the length of the dam, its construction often requires earthmoving on the very largest scale. Dams tend to be built in remote locations dictated by the need to ensure that water is available at a position where it is technically possible to restrict the flow of the river. Thus temporary roads may have to be built before dam building may start in order to get plant, materials and personnel to the site. Workers on dam projects may be so far from home that full-scale living accommodations have to be provided along with the usual construction site facilities. It is necessary to divert the river away from the site of the workings, and a coffer dam and temporary riverbed may have be created.
A dam constructed simply from earth or rock that has been shifted will require large scale excavation, digging and scraping plant as well as lorries. If the dam wall is covered by masonry or cast concrete, it will be necessary to employ high or long-reach cranes capable of depositing masonry, shuttering, reinforcing and concrete in the right places. A continuous supply of good-quality concrete will be necessary, and a concrete-mixing plant will be necessary alongside the dam workings, with the concrete either handled in batches by crane or pumped to the job.
Canals and docks
Construction and repair of canals and docks contain some aspects of other jobs that have been described, such as roadworks, tunnels and bridges. It is particularly important in canal building for surveying to be to the highest standard before work begins, especially regarding levels and to ensure that material that has had to be dug out can economically be used elsewhere in the job. Indeed the early railway engineers owed a great deal to the experience of canal builders a century before. The canal will require a source for its water and will either tap into a natural source such as a river or lake or create an artificial one in the form of a reservoir. Digging of docks may start on dry land, but sooner or later has to link up to either a river, a canal, the sea or another dock.
Canal and dock building requires excavators and loaders to open up the ground. Spoil may be removed by lorry or water transport may be used. Docks are sometimes developed on ground that has a long history of industrial use. Industrial wastes may have escaped into such ground over many years, and spoil removed in digging or extending the docks will be heavily contaminated. Work in repairing a canal or dock is likely to have to be carried out while adjacent parts of the system are kept in use. The workings may have to rely on coffer dams for protection. Failure of a coffer dam during extension of Newport Docks in Wales in the early years of this century resulted in nearly 100 deaths.
Clients for canals and docks are likely to be public authorities. However, sometimes docks are constructed for corporations alongside their major production plants or for corporate clients to handle a particular type of incoming or outgoing goods (e.g., motor cars). Repair and renovation of canals is nowadays often for the leisure industry. Like dams, both canal and dock construction may be in very remote situations, requiring provision of facilities for workers beyond those of a normal construction site.
Construction of railroads or railways historically came after canals and before major highways. Clients in railway construction contracts may be rail operators themselves or governmental agencies, if the railways are financed by government. As with highways, design of a railroad that is economical and safe to build and operate depends on good surveying beforehand. In general, locomotives do not operate effectively on steep gradients, and therefore those designing layout of the track are concerned with avoiding changes in levels, going round or through obstacles rather than over them.
Designers of railroads are subject to two constraints unique to the industry: first, curves in the track layout must generally conform to very large radii (otherwise trains cannot negotiate them); second, all the structures connected with the railway—its bridge arches, tunnels and stations—must be capable of accommodating the envelope of the largest locomotives and rolling stock that will use the track. The envelope is the silhouette of the rolling stock plus clearance to allow safe passage through bridges, tunnels and so on.
Contractors involved in building and repair of railroads require the usual construction plant and effective logistical arrangements to ensure that rail track and ballast as well as construction materials are always available in what may be remote locations. Contractors may use the track they have just laid to run trains supplying the works. Contractors involved in maintenance of existing operational railways have to ensure that their work does not interfere with the operations of the railway and endanger workers or the public.
The rapid expansion of air transportation since the middle of the 20th century has resulted in one of the biggest and most complex forms of construction: the building and extension of airports.
Clients for airport construction are usually governments at the national or local level or agencies representing the government. Some airports are built for major cities. Airports are rarely for private clients such as business corporations.
Planning the work is sometimes made more difficult because of environmental constraints that have been placed on the project in relation to noise and pollution. Airports require a lot of space, and if they are located in more heavily populated areas, creation of the runways and space for terminal buildings and car parks may require reinstatement of derelict or otherwise difficult land. Building an airport involves levelling a large area, which may require earth moving and even land reclamation, and then construction of a wide variety of often very large buildings, including hangars, maintenance workshops, control towers and fuel storage facilities, as well as terminal buildings and parking.
If the airport is being built on soft ground, buildings may require piled foundations. Actual runways require good foundations; hardcore supporting the surface layers of concrete or tarmac needs to be heavily compacted. Plant used on airport construction is similar in scale and type to that used in major highway projects, except that it is concentrated within a limited area rather than over the many miles of a highway.
Airport maintenance is a particularly difficult type of work where resurfacing the runways has to be integrated with continuing operation of the airport. Usually the contractor is allowed an agreed number of hours during the night when he or she can work on a runway that is temporarily taken out of use. All the contractor’s plant, materials and workforce have to be marshalled off the runways, prepared to move immediately to the work site at the agreed start time. The contractor must finish his or her work and get off the runways again at the agreed time when flights may resume. Whilst working on the runway, the contractor must not impede or otherwise endanger aircraft movement on other runways.
All new buildings and civil engineering structures go through the same cycle of conception or design, groundworks, building or erection (including the roof of a building), finishing and provision of utilities and final commissioning before being brought into use. In the course of years, those once new buildings or structures require maintenance including re-painting and cleaning; they are likely to be renovated by being updated or changed or repaired to correct damage by weather or accident; and finally they will need to be demolished to make way for a more modern facility or because their use is no longer required. This is true of houses; it is also true of large, complex structures like power stations and bridges. Each stage in the life of a building or civil engineering structure presents hazards, some of which are common to all work in construction (like the risk from falls) or unique to the particular type of project (such as the risk from collapse of excavations during preparation of foundations in either building or civil engineering).
For each type of project (and, indeed, each stage within a project) it is possible to forecast what will be the principal hazards to the safety of construction workers. The risk from falls is common to all construction projects, even those at ground level. This is supported by the evidence of accident data which show that up to half of fatal accidents to construction workers involve falls.
Physical hazards to those engaged in design of new facilities normally arise from visits by professional staff to carry out surveys. Visits by unaccompanied staff to unknown or abandoned sites may expose them to risks from dangerous access, unguarded openings and excavations and, in a building, to electrical wiring and equipment in a dangerous condition. If the survey requires entry into rooms or excavations that have been closed for some time, there is the risk of being overcome by carbon dioxide or reduced oxygen levels. All hazards are increased if visits are made to an unlit site after dark or if the lone visitor has no means of communicating with others and summoning aid. As a general rule, professional staff should not be required to visit sites where they will be on their own. They should not visit after dark unless the site is well lit. They should not enter enclosed spaces unless these have been tested and shown to be safe. Lastly, they should be in communication with their base or have an effective means of getting help.
Conception or design proper should play an important part in influencing safety when contractors are actually working onsite. Designers, be they architects or civil engineers, should be expected to be more than mere producers of drawings. In creating their design, they should, by reason of their training and experience, have some idea how contractors are likely to have to work in putting the design into effect. Their competence should be such that they are able to identify to contractors the hazards that will arise from those methods of working. Designers should try to “design out” hazards arising from their design, making the structure more “buildable” as regards health and safety and, where possible, substituting safer materials in the specifications. They should improve access for maintenance at the design stage and reduce the need for maintenance workers to be put at risk by incorporating features or materials that will require less frequent attention during the life of the building.
In general, designers are able to design out hazards only to a limited extent; there will usually be significant residual risks that the contractors will have to take into account when devising their own safe systems of work. Designers should provide contractors with information on these hazards so that the latter are able to take both the hazards and necessary safety procedures into account, firstly when tendering for the job, and secondly when developing their systems of work to do the job safely.
The importance of specifying materials with better health and safety properties tends to be underestimated when considering safety by design. Designers and specifiers should consider whether materials are available with better toxic or structural properties or that can be used or maintained more safely. This requires designers to think about the materials that will be used and to decide whether following previous practice will adequately protect construction workers. Often cost is the determining factor in choice of materials. However, clients and designers should realize that while materials with better toxic or structural properties may have a higher initial cost, they often yield much bigger savings over the life of the building because construction and maintenance workers require less expensive access or protective equipment.
Usually the first job to be done on the site after site surveys and laying out of the site once the contract has been awarded (assuming there is no need for demolition or site clearance) is groundworks for the foundations. In the case of domestic housing, the footings are unlikely to require excavations greater than half a metre and may be dug by hand. For blocks of flats, commercial and industrial buildings and some civil engineering, the foundations may need to be several metres below ground level. This will require the digging of trenches in which work will have to carried out to lay or erect the foundations. Trenches deeper than 1 m are likely to be dug using machines such as excavators. Excavations are also dug to permit laying of cables and pipes. Contractors often use special-purpose excavators capable of digging deep but narrow excavations. If workers have to enter these excavations, the hazards are essentially the same as those encountered in excavations for foundations. However, there is usually more scope in cable and pipe excavations or trenches to adopt methods of working that do not require workers to enter the excavation.
Work in excavations deeper then 1 m needs especially careful planning and supervision. The hazard is the risk of being struck by earth and debris as the ground collapses along the side of the excavation. Ground is notoriously unpredictable; what looks firm can be caused to slip by rain, frost or vibration from other construction activities nearby. What looks like firm, stiff clay dries out and cracks when exposed to the air or will soften and slip after rain. A cubic metre of earth weighs more than 1 tonne; a worker struck by only a small fall of ground risks broken limbs, crushed internal organs and suffocation. Because of the vital importance to safety of selecting a suitable method of support for the sides of the excavation, before work starts, the ground should be surveyed by a person experienced in safe excavation work to establish the type and condition of the ground, especially the presence of water.
Support for trench sides
Double-sided support. It is not safe to rely on cutting or “battering” back the sides of the excavation to a safe angle. If the ground is wet sand or silt, the safe angle of batter would be as low as 5 to 10 above horizontal, and there is generally not enough room onsite for such a wide excavation. The most common method of providing safety for work in excavations is to support both sides of the trench through shoring. With double-sided support, the loads from the ground on one side are resisted by similar loads acting through struts between the opposing sides. Timber of good quality must be used to provide vertical elements of the support system, known as poling boards. Poling boards are driven into the ground as soon as excavation begins; the boards are edge to edge, and thus provide a timber wall. This is done on each side of the excavation. As the excavation is dug deeper, the poling boards are driven into the ground ahead of the excavation. When the excavation is a metre deep, a row of horizontal boards (known as walings or wales) is placed against the poling boards and then held in position by timber or metal struts wedged between the opposing walings at regular intervals. As digging proceeds, the poling boards are driven further into the ground with their walings and struts, and it will be necessary to create a second row of walings and struts if the excavation is deeper than 1.2 m. Indeed, an excavation of 6 m could require up to four rows of walings.
The standard timber methods of support are unsuitable if the excavation is deeper than 6 m or the ground is water bearing. In these situations, other types of support for the sides of excavations are required, such as vertical steel trench sheets, closely spaced with horizontal timber walings and metal adjustable struts, or full-scale steel sheet piling. Both methods have the advantage that the trench sheets or sheet piles can be driven by machine before excavation proper starts. Also, trench sheets and sheet piles can be withdrawn at the end of the job and re-used. Support systems for excavations deeper than 6 m or in water-bearing ground should be custom designed; standard solutions will not be adequate.
Single-sided support. An excavation that is rectangular in shape and too large for the support methods described above to be practicable may have one or more of its sides supported by a row of poling boards or trench sheets. These are themselves supported first by one or more rows of horizontal walings which are themselves then held in place by angled rakes back to a strong anchorage or support point.
Other systems. It is possible to use manufactured steel boxes of adjustable width that may be lowered into excavations and within which work can be carried out safely. It is also possible to use proprietary waling frame systems, whereby a horizontal frame is lowered into the excavation between the poling boards or trench sheets; the waling frame is forced apart and applies pressure to keep the poling boards upright by the action of hydraulic struts across the frame which can be pumped from a position of safety outside the excavation.
Training and supervision. Whatever method of support is adopted, the work should be carried out by trained workers under supervision of an experienced person. The excavation and its supports should be inspected each day and after each occasion that they have been damaged or displaced (e.g., after a heavy rain). The only assumption one is entitled to make regarding safety and work in excavations is that all ground is liable to fail and therefore no work should ever be carried out with workers in an unsupported excavation deeper than 1 m. See also the article “Trenching” in this chapter.
Erection of the main part of the building or civil engineering structure (the superstructure) takes place after completion of the foundation. This part of the project usually requires work at heights above ground. The biggest single cause of fatal and major injury accidents is falls from heights or on the same level.
Even if the job is simply building a house, the number of workers involved, the amount of building materials to be handled and, in later stages, the heights at which work will have to be carried out all require more than simple ladders for access and safe places of work.
There are limitations on the sort of work that can be done safely from ladders. Work more than 10 m above ground is usually beyond the safe reach of ladders; lengthy ladders themselves become dangerous to handle. There are limitations on the reach of workers on ladders as well as on the amount of equipment and materials they can safely carry; the physical strain of standing on ladder rungs limits the time they can spend on such work. Ladders are useful for carrying out short-duration, light-weight work within safe reach of the ladder; typically, inspection and repair and painting of small areas of the building’s surface. Ladders also provide access in scaffolds, in excavations and in structures where more permanent access has not yet been provided.
It will be necessary to use temporary working platforms, the most common of which is scaffolding. If the job is a multi-storey block of flats, office building or structure like a bridge, then scaffolding of varying degrees of complexity will be required, depending on the scale of the job.
Scaffolds consist of easily assembled frameworks of steel or timber on which working platforms may be placed. Scaffolds may be fixed or mobile. Fixed scaffolds—that is, those erected alongside a building or structure—are either independent or putlog. The independent scaffold has uprights or standards along both sides of its platforms and is capable of remaining upright without support from the building. The putlog scaffold has standards along the outer edges of its working platforms, but the inner side is supported by the building itself, with parts of the scaffold frame, the putlogs, having flattened ends that are placed between courses of brickwork to gain support. Even the independent scaffold needs to be rigidly “tied” or secured to the structure at regular intervals if there are working platforms above 6 m or if the scaffold is sheeted for weather protection, thus increasing wind-loadings.
Working platforms on scaffolds consist of good-quality timber boards laid so that they are level and both ends are properly supported; intervening supports will be necessary if the timber is liable to sag due to loading by people or materials. Platforms should never be less than 600 mm in width if used for access and working or 800 mm if used also for materials. Where there is a risk of falling more than 2 m, the outer edge and ends of a working platform should be protected by a rigid guard rail, secured to the standards at a height of between 0.91 and 1.15 m above the platform. To prevent materials falling off the platform, a toe board rising at least 150 mm above the platform should be provided along its outer edge, again secured to the standards. If guard rails and toe-boards have to be removed to permit passage of materials, they should be replaced as soon as possible.
Scaffold standards should be upright and properly supported at their bases on base plates, and if necessary on timber. Access within fixed scaffolds from one working platform level to another is usually by means of ladders. These should be properly maintained, secured at top and bottom and extend at least 1.05 m above the platform.
The principal hazards in the use of scaffolds—falls of person or materials—usually arise from shortcomings either in the way the scaffold is first erected (e.g., a piece such as a guard rail is missing) or in the way it is misused (e.g., by being overloaded) or adapted during the course of the job for some purpose that is unsuitable (e.g., sheeting for weather protection is added without adequate ties to the building). Timber boards for scaffold platforms become displaced or break; ladders are not secured at top and bottom. The list of things that can go wrong if scaffolds are not erected by experienced persons under proper supervision is almost limitless. Scaffolders are themselves particularly at risk from falls during erection and dismantling of scaffolds, because they are often obliged to work at heights, in exposed positions without proper working platforms (see figure 1).
Figure 1. Assembling scaffolding at a Geneva, Switzerland, construction site without adequate protection.
Tower scaffolds. Tower scaffolds are either fixed or mobile, with a working platform on top and an access ladder inside the tower frame. The mobile tower scaffold is on wheels. Such towers easily become unstable and should be subject to height limitations; for the fixed tower scaffold the height should not be more than 3.5 times the shortest base dimension; for mobile, the ratio is reduced to 3 times. The stability of tower scaffolds should be increased by use of outriggers. Workers should not be permitted on the top of mobile tower scaffolds while the scaffold is being moved or without the wheels being locked.
The principal hazard with tower scaffolds is overturning, throwing people off the platform; this may be due to the tower being too tall for its base, failure to use outriggers or lock wheels or unsuitable use of the scaffold, perhaps by overloading it.
Slung and suspended scaffolds. The other main category of scaffold is those that are slung or suspended. The slung scaffold is essentially a working platform hung by wire ropes or scaffold tubes from an overhead structure like a bridge. The suspended scaffold is again a working platform or cradle, suspended by wire ropes, but in this case it is capable of being raised and lowered. It is often provided for maintenance and painting contractors, sometimes as part of the equipment of the finished building.
In either case, the building or structure must be capable of supporting the slung or suspended platform, the suspension arrangements must be strong enough and the platform itself should be sufficiently robust to carry the intended load of people and materials with guard sides or rails to prevent them from falling out. For the suspended platform, there should be at least three turns of rope on the winch drums at the lowest position of the platform. Where there are no arrangements to prevent the suspended platform from falling in the event of failure of a rope, workers using the platform should wear a safety harness and rope attached to a secure anchorage point on the building. Persons using such platforms should be trained and experienced in their use.
The principal hazard with slung or suspended scaffolds is failure of the supporting arrangements, either of the structure itself or the ropes or tubes from which the platform is hung. This can arise from incorrect erection or installation of the slung or suspended scaffold or from overloading or other misuse. Failure of suspended scaffolds has resulted in multiple fatalities and can endanger the public.
All scaffolds and ladders should be inspected by a competent person at least weekly and before being used again after weather conditions that may have damaged them. Ladders which have cracked styles or broken rungs should not be used. Scaffolders who erect and dismantle scaffolds should be given specific training and experience to ensure their own safety and the safety of others who may use the scaffolds. Scaffolds are often provided by one, perhaps the main, contractor for use by all contractors. In this situation, tradespeople may modify or displace parts of scaffolds to make their own job easier, without restoring the scaffold afterwards or realizing the hazard they have created. It is important that the arrangements for coordination of health and safety across the site deal effectively with the action of one trade on the safety of another.
Powered access equipment
On some jobs, during both construction and maintenance, it may be more practicable to use powered access equipment than scaffolding in its various forms. Providing access to the underside of a factory roof undergoing recladding or access to the outside of a few windows in a building may be safer and cheaper than scaffolding out the whole structure. Powered access equipment comes in a variety of forms from manufacturers, for example, platforms that may be raised and lowered vertically by hydraulic action or the opening and closing of scissor jacks and hydraulically-powered articulated arms with a working platform or cage on the end of the arm, commonly called cherry pickers. Such equipment is generally mobile and can be moved to the place it is required and brought into use in a matter of moments. Safe use of powered access equipment requires that the job be within the specification for the machine as described by the manufacturer (i.e., the equipment must not overreach or be overloaded).
Powered access equipment requires a firm, level floor on which to operate; it may be necessary to put out outriggers to ensure that the machine does not tip over. Workers on the working platform should have access to operating controls. Workers should be trained in safe use of such equipment. Properly operated and maintained, powered access equipment can provide safe access where it may be virtually impossible to provide scaffolding, for example, during the early stages of erection of a steel frame or to provide access for steel erectors to the connecting points between columns and beams.
The superstructure of both buildings and civil engineering structures often involves erection of substantial steel frames, sometimes of great height. While responsibility for ensuring safe access for steel erectors who assemble these frames rests principally with the management of steel erection contractors, their difficult job can be made easier by the designers of the steel work. Designers should ensure that patterns of bolt holes are simple and facilitate easy insertion of bolts; the pattern of joints and bolt holes should be as uniform as possible throughout the frame; rests or perches should be provided on columns at joints with beams, so that the ends of beams may rest still while steel erectors are inserting bolts. As far as possible, the design should ensure that access stairs form part of the early frame so that steel erectors have to rely less on ladders and beams for access.
Also, the design should provide for holes to be drilled in suitable places in the columns during fabrication and before the steel is delivered to site, which will permit securing of taut wire ropes, to which steel erectors wearing safety harnesses may secure their running lines. The aim should be to get floor plates in place in steel frames as soon as possible, to reduce the amount of time that steel erectors have to rely on safety lines and harnesses or ladders. If the steel frame has to remain open and without floors while erection continues to higher levels, then safety nets should be slung below the various working levels. As far as possible, the design of the steel frame and the working practices of the steel erectors should minimize the extent to which workers have to “walk steel”.
While raising the walls is an important and hazardous stage in erecting a building, putting the roof in place is equally important and presents special hazards. Roofs are either flat or pitched. With flat roofs the principal hazard is of persons or materials falling either over the edge or down openings in the roof. Flat roofs are usually constructed either from wood or cast concrete, or slabs. Flat roofs must be sealed against entry of water, and various materials are used, including bitumen and felt. All materials required for the roof have to be raised to the required level, which may require goods hoists or cranes if the building is tall or the quantities of covering and sealant are substantial. Bitumen may have to be heated to assist spreading and sealing; this may involve taking on to the roof a gas cylinder and melting pot. Roof-workers and persons beneath can be burned by the heated bitumen and fires can be started involving the roof structure.
The hazard from falls can be prevented on flat roofs by erecting temporary edge protection in the form of guard rails of dimensions similar to the guard rails in scaffolds. If the building is still surrounded by external scaffolding, this can be extended up to roof level, to provide edge protection for roof-workers. Falls down openings in flat roofs can be prevented by covering them or, if they have to remain open, by erecting guard rails round them.
Pitched roofs are most commonly found on houses and smaller buildings. The pitch of the roof is achieved by erecting a wooden frame to which the outer covering of the roof, usually clay or concrete tiles, is attached. The pitch of the roof may exceed 45 above horizontal, but even a shallower pitch presents hazards when wet. To prevent roof-workers from falling while fixing battens, felt and tiles, roof ladders should be used. If the roof ladder cannot be secured or supported at its bottom end, it should have a properly designed ridge-iron that will hook over the ridge tiles. Where there is doubt about the strength of ridge tiles, the ladder should be secured by means of a rope from its top rung, over the ridge tiles and down to a strong anchorage point.
Fragile roofing materials are used on both pitched and curved or barrel roofs. Some roof lights are made of fragile materials. Typical materials include sheets of asbestos cement, plastic, treated chipboard and wood-wool. Because roof-workers frequently step through sheets they have just laid, safe access to where the sheets are to be laid, and a safe position from which to do it, are required. This is usually in the form of a series of roof ladders. Fragile roofing materials present an even greater hazard to maintenance workers, who may be unaware of their fragile nature. Designers and architects can improve the safety of roof-workers by not specifying fragile materials in the first place.
Laying of roofs, even flat roofs, can be dangerous in high winds or heavy rain. Materials such as sheets, normally safe to handle, become dangerous in such weather. Unsafe roof-work not only endangers roof-workers, but also presents hazards to the public beneath. Erection of new roofs is hazardous, but, if anything, maintenance of roofs is even more dangerous.
Renovation includes both maintenance of the structure and changes to it during its life. Maintenance (including cleaning and repainting of woodwork or other exterior surfaces, repointing of cement and repairs to walls and the roof) presents hazards from falling similar to those of erection of the structure because of the need to gain access to high parts of the structure. Indeed, the hazards may be greater because during smaller, short-duration maintenance jobs, there is a temptation to cut costs on provision of safe access equipment, for example, by trying to do from a ladder what can be safely done only from a scaffold. This is especially true of roof work, where replacement of a tile may take only minutes but there is still the possibility of a worker falling to his or her death.
Maintenance and cleaning
Designers, especially architects, can improve safety for maintenance and cleaning workers by taking into account in their designs and specifications the need for safe access to roofs, to plant rooms, to windows and to other exposed positions on the outside of the structure. Avoiding the need for access at all is the best solution, followed next by permanent safe access as part of the structure, perhaps stairs or a walkway with guard rails or a powered access platform permanently slung from the roof. The least satisfactory situation for maintenance personnel is where a scaffold similar to that used to erect the building is the only way to provide safe access. This will be less of a problem for major, longer duration renovation work, but on short-duration jobs, the cost of full scaffolding is such that there is a temptation to cut corners and use mobile powered access equipment or tower scaffolds where they are unsuitable or inadequate.
If renovation involves major re-cladding of the building or wholesale cleaning using high-pressure water jetting or chemicals, total scaffolding may be the only answer that will not only protect the workers but also allow the hanging of sheeting to protect the public nearby. Protection of workers involved in cleaning using high-pressure water jets includes impervious clothing, boots and gloves, and a face screen or goggles to protect the eyes. Cleaning involving chemicals such as acids will require similar but acid-resistant protective clothing. If abrasives are used to clean the structure a silica-free substance should be used. Since use of abrasives will give rise to dust that may be injurious, approved respiratory equipment should be worn by the workers. Repainting of windows in a tall office building or block of flats cannot be done safely from ladders, although this is usually possible on domestic housing. It will be necessary to provide either scaffolding or to hang suspended scaffolds such as cradles from the roof, ensuring that suspension points are adequate.
Maintenance and cleaning of civil engineering structures, like bridges, tall chimneys or masts may involve working at such heights or in such positions (e.g., above water) that prohibit the erection of a normal scaffold. As far as possible, work should be done from a fixed scaffold slung or cantilevered from the structure. Where this is not possible, work should be done from a properly suspended cradle. Modern bridges often have their own cradles as parts of the permanent structure; these should be checked fully before being used for a maintenance job. Civil engineering structures are often exposed to the weather, and work should not be permitted in high winds or heavy rain.
Window cleaning presents its own hazards, especially where it is done from the ground on ladders, or with improvised arrangements for access on taller buildings. Window cleaning is not usually regarded as part of the construction process, and yet is a widespread operation that can endanger both the window cleaners and the public. Safety in window cleaning is, however, influenced by one part of the construction process-design. If architects fail to take into account the need for safe access, or alternatively to specify windows of a design that can be cleaned from inside, then the job of the window cleaning contractor will be much more hazardous. Whilst designing out the need for external window cleaning or installing proper access equipment as part of the original design may initially cost more, there should be considerable savings over the life of the building in maintenance costs and a reduction in hazards.
Refurbishment is an important and hazardous aspect of renovation. It takes place when for example, the essential structure of the building or bridge is left in place but other parts are repaired or replaced. Typically in domestic housing, refurbishment involves stripping out windows, possibly floors and stairs, along with wiring and plumbing, and replacing them with new and usually upgraded items. In a commercial office building, refurbishment involves windows and possibly floors, but also is likely to involve stripping out and replacing cladding to a framed building, installing new heating and ventilation equipment and lifts or total rewiring.
In civil engineering structures such as bridges, refurbishment may involve stripping the structure back to its basic frame, strengthening it, renewing parts and replacing the roadway and any cladding.
Refurbishment presents the usual hazards to construction workers: falling and falling materials. The hazard is made more difficult to control where the premises remain occupied during refurbishment, as is often the case in domestic premises such as blocks of flats, when alternative accommodations to house occupants are simply not available. In that situation the occupants, especially children, face the same hazards as construction workers. There may be hazards from power cables to portable tools such as saws and drills required during refurbishment. It is important that the work be carefully planned to minimize hazards to both workers and the public; the latter need to know what will be going on and when. Access to rooms, stairs or balconies where work is to be carried out should be prevented. Entrances to blocks of flats may have to be protected by fans to protect persons from falling materials. At the close of the working shift, ladders and scaffolds should be removed or closed off in a manner that does not allow children to get onto them and endanger themselves. Similarly, paints, gas cylinders and power tools should be removed or stored safely.
In occupied commercial buildings where services are being refurbished, it should not be possible for liftway doors to be opened. If refurbishment interferes with fire and emergency equipment, special arrangements need to be made to warn both occupants and workers if fire breaks out. Refurbishment of both domestic and commercial premises may require removal of asbestos-containing materials. This presents major health risks to the workers and the occupants when they return. Such asbestos removal should be carried out only by specially trained and equipped contractors. The area where asbestos is being removed will need to be sealed off from other parts of the building. Before the occupants return to areas from which asbestos has been stripped, the atmosphere in those rooms should be monitored and the results evaluated to ensure that asbestos fibre levels in air are below permissible levels.
Usually the safest way to carry out refurbishment is to totally exclude occupants and members of the public; however, this is sometimes simply not practicable.
Provision of utilities in buildings, such as electricity, gas, water and telecommunications, is usually carried out by specialist subcontractors. Principal hazards are falls due to poor access, dust and fumes from drilling and cutting and electric shock or fire from electrical and gas services. The hazards are the same in houses, only on a smaller scale. The job is easier for contractors if proper allowance has been made by the architect in designing the structure to accommodate the utilities. They require space for ducts and channels in walls and floors plus sufficient additional space for installers to operate effectively and safely. Similar considerations apply to maintenance of utilities after the building has been taken into use. Proper attention to the detailing of ducts, channels and openings in the initial design of the structure should mean that these are either cast or built into the structure. It will then not be necessary for construction workers to chase out channels and ducts or to open up holes using power tools, which create large quantities of harmful dust. If adequate space is provided for heating and air conditioning ducts and equipment, the job of the installers is both easier and safer because it is then possible to work from safe positions rather than, for example, standing on boards wedged across the inside of vertical ducts. If lighting and wiring have to be installed overhead in rooms with high ceilings, contractors may need scaffolding or tower scaffolds in addition to ladders.
Installation of utility services should be conform to recognized local standards. These should, for example, cover all safety aspects of electrical and gas installations so that contractors are in no doubt as to standards required for wiring, insulation, earthing (grounding), fusing, isolation and, for gas, protection for pipework, isolation, adequate ventilation and fitting of safety devices for flame failure and loss of pressure. Failure by contractors to deal adequately with these matters of detail in the installation or maintenance of utilities will create hazards for both their own workers and the occupants of the building.
If the structure is of brick or concrete, the interior finish may require initial plastering to provide a surface which can be painted. Plastering is a traditional craft trade. The principal hazards are severe strain to the back and arms from handling bagged material and plaster boards and then the actual plastering process, especially when the plasterer is working overhead. After plastering, surfaces may be painted. The hazard here is from vapours given off by thinners or solvents and sometimes from the paint itself. If possible, water-based paints should be used. If solvent-based paints have to be used, the rooms should be well ventilated, if necessary by the use of fans. If materials used are toxic and adequate ventilation cannot be achieved, then respiratory and other personal protection should be worn.
Sometimes interior finishing may require the fixing of cladding or linings to the walls. If this involves use of cartridge guns to secure the panels to timber studding the hazard will principally arise from the way the gun is operated. Cartridge-driven nails can easily be fired through walls and partitions or can ricochet on striking something hard. Contractors need to plan this work carefully, if necessary excluding other persons from the vicinity.
Finishing may require tiles or slabs of various materials to be fixed to walls and floors. Cutting large quantities of ceramic tiles or stone slabs using powered cutters gives rise to great quantities of dust and should either be done wet or in an enclosed area. The principal hazard with tiles, including carpet tiles, arises from the need to stick them in position. Adhesives used are solvent based and give off vapours that are harmful, and in an enclosed space they can be flammable. Unfortunately, those laying tiles are kneeling down low over the point where vapours are given off. Water-based adhesives should be used. Where solvent-based adhesives have to be used, rooms should be well ventilated (fan assisted), the quantity of adhesives brought into the workroom should be kept to a minimum and drums should be decanted into smaller tins used by tilers outside the workroom.
If finishing requires installations of sound- or heat-insulation materials, as is often the case in blocks of flats and commercial buildings, these may be in the form of sheets or slabs that are cut, blocks that are laid and fixed together or to a surface by a cement or in a wet form that is sprayed. Hazards include exposure to dust that may both irritate and be harmful. Asbestos-containing materials should not be used. If artificial mineral fibres are used, respiratory protection and protective clothing should be worn to prevent skin irritation.
Fire hazards in interior finishing
Many of the finishing operations in a building involve use of materials that greatly increase the fire hazard. The basic structure may be relatively non-flammable steel, concrete and brick. However, the finishing trades introduce wood, possibly paper, paints and solvents.
At the same time that interior finishing is being performed work may be going on nearby using electric powered tools, or the electrical services may be being installed. Nearly always there is a source of ignition for flammable vapour and materials used in finishing. Many very costly fires have been ignited during finishing, putting workers at risk and usually damaging not only the finishing of the building but also its main structure. A building undergoing finishing is an enclosure in which possibly hundreds of workers are using flammable materials. The main contractor should ensure that proper arrangements are made to provide and protect means of escape, keep access routes clear from obstructions, reduce the quantity of flammable materials stored and in use inside the building, warn contractors of fire and, when necessary, evacuate the building.
Some of the materials used in internal finishing may also be used on the exterior, but exterior finishing is generally concerned with cladding, sealing and painting. The cement courses in brick and block work are generally “pointed” or finished as the bricks or blocks are laid and require no further attention. The exterior of walls may be cement that is to be painted or have an application of a layer of small stones, as in stucco or roughcast. Exterior finishing, like general construction work, is done outdoors and is subject to the effects of the weather. By far the greatest hazard is the risk of falling, often heightened by difficulties in handling components and materials. Use of paints, sealants and adhesives containing solvents is less of a problem than in internal finishing because natural ventilation prevents a build-up of harmful or flammable concentrations of vapour.
Again, designers can influence the safety of exterior finishing by specifying cladding panels that can be safely handled (i.e., not too heavy or large) and making arrangements so that cladding can be done from safe positions. The frames or floors of the building should be designed to incorporate features like lugs or recesses that permit easy landing of cladding panels, especially when placed in position by crane or hoist. Specification of materials such as plastics for window frames and fascias eliminates the need for painting and repainting and reduces subsequent maintenance. This benefits the safety of both construction workers and the occupants of house or flat.
Landscaping on a large scale may involve earth-moving similar to that involved in highway and canal works. It may require deep excavations to install drains; extensive areas may have to be slabbed or concreted; rocks may have to be moved. Finally, the client may wish to create the impression of a mature, well-established development, so that fully grown trees will be planted. All of this requires excavation, digging and loading. It often also requires considerable lifting capacity.
Landscape contractors are usually specialists who do not spend much of their time working as part of construction contracts. The main contractor should ensure that landscape contractors are brought to the site at an appropriate time (not necessarily towards the end of the contract). Major excavation and pipe laying may best be carried out early in the life of the project, when similar work is being done for the foundations of the building. Landscaping must not undermine or endanger the building or overload the structure by heaping earth on or against it and its outbuildings in a dangerous manner. If topsoil is to be removed and later placed back in position, sufficient space to heap it in a safe manner will have to be provided.
Landscaping may also be required at industrial premises and public utilities for safety and environmental reasons. Around a petrochemical plant it may be necessary to level off the ground or provide a particular direction of slope, possibly covering the ground with stone chips or concrete to prevent the growth of vegetation. On the other hand, if landscaping around industrial premises is intended to improve appearance or environmental reasons (e.g., to reduce noise or hide an unsightly plant), it may require embankments and erection of screens or planting of trees. Highways and railroad tracks today have to include features that will reduce noise if they are near urban areas or hide the operations if they are in environmentally sensitive areas. Landscaping is not just an afterthought, because as well as improving the appearance of the building or plant, it may, depending on the nature of the development, preserve the environment and improve safety generally. Therefore, it needs to be designed and planned as an integral part of the project.
Demolition is perhaps the most dangerous construction operation. It has all the hazards of working at heights and being struck by falling materials, but it is carried out in a structure that has been weakened either as part of the demolition, or as the result of storms, damage produced by flood, fire, explosions or simple wear and tear. The hazards during demolition are falls, being struck or buried in falling material or by the unintentional collapse of the structure, noise and dust. One of the practical problems with ensuring health and safety during demolition is that it can proceed very rapidly; with modern equipment a great deal can be demolished in a couple of days.
There are three principal ways of demolishing a structure: take it down piecemeal; knock it or push it down; or blast it down using explosives. Choice of method is dictated by the condition of the structure, its surroundings, the reasons for the demolition and cost. Use of explosives will usually not be possible when other buildings are close by. Demolition needs to be planned as carefully as any other construction process. The structure to be demolished should be thoroughly surveyed and any drawings obtained, so that as much information as possible on the nature of the structure, its method of construction and materials is available to the demolition contractor. Asbestos is commonly found in buildings and other structures that are to be demolished and requires contractors who are specialists in handling it.
Planning of the demolition process should ensure that the structure is not overloaded or unevenly loaded with debris and that there are suitable openings for chuting of debris for safe removal. If the structure is to be weakened by cutting parts of the frame (especially reinforced concrete or other highly stressed types of structure) or by removing parts of a building such as floors or internal walls, this must not so weaken the structure that it may collapse unexpectedly. Debris and scrap materials should be planned to fall in such a way that they can be removed or saved safely and appropriately; sometimes the cost of a demolition job depends on salvaging valuable scrap or components.
If the structure is to be demolished piecemeal (i.e., taken down bit by bit), without using remotely operated powered picks and cutters, workers will inevitably have to do the job using hand tools or hand-held powered tools. This means they may have to work at heights on exposed faces or above openings created to allow debris to fall. Accordingly, temporary scaffold working platforms will be necessary. The stability of such scaffolds should not be endangered by removal of parts of the structure or fall of debris. If stairs are no longer available for use by workers because the stairwell opening is being used to chute debris external ladders or scaffolds will be necessary.
Removal of points, spires or other tall features on the top of buildings is sometimes done most safely by workers operating from properly-designed buckets slung from the safety hook of a crane.
In piecemeal demolition, the safest method is to take the building down in a sequence opposite to the way it was put up. Debris should be removed regularly so that working places and access do not become obstructed.
If the structure is to be pushed or pulled over or knocked down, it is usually pre-weakened, with the attendant hazards. Pulling down is sometimes done by removing floors and internal walls, attaching wire ropes to strong points on the upper parts of the building and using an excavator or other heavy machine to pull on the wire rope. There is a real hazard from flying wire ropes if they break due to overload or failure of the anchorage point on the building. This technique is not suitable for very tall buildings. Pushing over, again after pre-weakening, involves use of heavy plant such as crawler-mounted grabs or pushers. The cabs of such equipment should be shielded to prevent drivers from being injured by falling debris. The site should not be allowed to become so obstructed by fallen debris as to create instability for machine used to pull or push the building down.
The most common form of demolition (and if done properly, in many ways the safest) is “balling” down, using a steel or concrete ball suspended from a hook on a crane with a jib strong enough to withstand the special strains imposed by balling. The jib is moved sideways and the ball swung against the wall to be demolished. The principal hazard is trapping the ball in the structure or debris, then trying to extricate it by raising the crane hook. This grossly overloads the crane, and either the crane cable or the jib may fail. It may be necessary for a worker to climb up to where the ball is wedged and free it. However, this should not be done if there is a risk of that part of the building collapsing on the worker. Another hazard associated with less skilled crane operators is balling too hard, so that unintended parts of the building are accidentally brought down.
Demolition using explosives can be done safely, but it must be carefully planned and carried out only by experienced workers under competent supervision. Unlike military explosives, the purpose of blasting to demolish a building is not to totally reduce the building to a heap of rubble. The safe way to do it is, after pre-weakening, to use no more explosive than will safely bring down the structure so that debris can be safely removed and scrap salvaged. Contractors carrying out blasting should survey the structure, obtain drawings and as much information as possible on its method of construction and materials. Only with this information is it possible to determine whether blasting is appropriate in the first place, where charges should be placed, how much explosive should be used, what steps may be necessary to prevent ejection of debris and what sort of separation zones will be required around the site to protect workers and the public. If there are a number of explosive charges, electrical shotfiring with detonators will usually be more practical, but electrical systems can develop faults, and on simpler jobs the use of detonator cord may be more practical and safer. Aspects of blasting that require careful preliminary planning are what is to be done if there is either a misfire or if the structure does not fall as planned and is left hanging in a dangerous state of instability. If the job is close to housing, highways or industrial developments, the people in the area should be warned; local police are usually involved in clearing the area and halting pedestrian and vehicular traffic.
Tall structures like television towers or cooling towers may be felled using explosives, providing they have been pre-weakened so that they fall safely.
Demolition workers are exposed to high noise levels because of noisy machinery and tools, falling debris or blasts from explosives. Hearing protection will usually be required. Dust is produced in large quantities as buildings are demolished. A preliminary survey should ascertain whether and where lead or asbestos are present; if possible, these should be removed before the start of the demolition. Even in the absence of such notable hazards, dust from demolition is often irritating if not actually injurious, and an approved dust mask should be worn if the work area cannot be kept wet to control the dust.
Demolition is both dirty and arduous, and a high level of welfare facilities should be provided, including toilets, washplaces, cloakrooms for both normal clothing and work clothes and a place to shelter and take meals.
Dismantling differs from demolition in that part of the structure or, more commonly, a large piece of machinery or equipment is disassembled and removed from site. For example, removal of part or the whole of a boiler from a power house in order to replace it, or replacement of a steel girder bridge span is dismantling rather than demolition. Workers involved in dismantling tend to do a great deal of oxyacetylene or gas cutting of steel work, either to remove parts of the structure or to weaken it. They may use explosives to knock over an item of equipment. They use heavy lifting machinery to remove large girders or pieces of machinery.
Generally, workers engaged in such activities face all the same hazards of falling, things falling on them, noise, dust and harmful substances that are met in demolition proper. Contractors who carry out dismantling require a sound knowledge of structures to ensure that they are taken apart in a sequence that does not cause a sudden and unexpected collapse of the main structure.
Work over and alongside water as in bridge building and maintenance, in docks and sea and river defence work presents special hazards. The hazard may be increased if the water is flowing or tidal, as opposed to still; rapid water movement makes it more difficult to rescue those who fall in. Falling in water presents the hazard of drowning (in even quite shallow water if the person is injured in the fall as well as hypothermia if the water is cold and infection if it is polluted).
The first precaution is to prevent workers from falling by ensuring that there are proper walkways and workplaces with guard rails. These should not be allowed to become wet and slippery. If walkways are not possible, as perhaps in the earlier stages of steel erection, the workers should wear harnesses and ropes attached to secure anchorage points. These should be supplemented with safety nets slung beneath the work position. Ladders and grablines should be provided to assist fallen workers to climb out of the water, as, for example, at the edges of docks and sea defences. While workers are not on a properly boarded out platform with guard rails or are travelling to and from their worksite, they should wear buoyancy aids. Lifebuoys and rescue lines should be placed at regular intervals along the edge of the water.
Work in docks, river maintenance and sea defences often involves use of barges to carry piling rigs and excavators to remove dredged out spoil. Such barges are equivalent to working platforms and should have suitable guard rails, lifebuoys and rescue and grab lines. Safe access from the shore, dock or river side should be provided in the form of walkways or gangways with guard rails. This should be so arranged as to adjust safely with the changing levels of tidal water.
Rescue boats should be available, fitted with grablines and with lifebuoys and rescue lines on board. If the water is cold or flowing, the boats should be continuously staffed, and should be powered and ready to carry out a rescue mission immediately. If water is polluted with industrial effluent or sewage, arrangements should be made to transport those who fall into such water to a medical centre or hospital for immediate treatment. Water in urban areas may be contaminated with the urine of rats, which may infect open skin abrasions, causing Weil’s disease.
Work over water is often carried out in locations that are subject to strong winds, driving rain or icing conditions. These increase the risk of falls and heat loss. Severe weather may make it necessary to stop work, even in the middle of a shift; to avoid excessive heat loss it may be necessary to supplement normal wet or cold weather protective clothing with thermal underclothing.
Diving is a specialized form of working underwater. The hazards faced by divers are drowning, decompression sickness (or the “bends”), hypothermia from the cold and becoming trapped below water. Diving may be required during construction or maintenance of docks, sea and river defences and at piers and abutments of bridges. It is often required in waters where visibility is poor or in locations where there is a risk of entanglement for the diver and his or her equipment. Diving may be carried out from dry land or from a boat. If the work requires only a single diver, then as a minimum a team of three will be required for safety. The team consists of the diver in the water, a fully equipped standby diver ready to enter the water immediately in the event of an emergency and a diving supervisor in charge. The diving supervisor should be at the safe position on land or in the boat from which the diving is to take place.
Diving at depths less than 50 m is usually carried out by divers wearing wet suits (i.e., suits that do not exclude water) and wearing self-contained underwater breathing apparatus with an open face mask (i.e., SCUBA diving gear). At depths greater than 50 m or in very cold water, it will be necessary for divers to wear suits that are heated by a supply of pumped warm water and closed diving masks, and equipment for breathing not compressed air but air plus a mixture of gases (i.e., mixed-gas diving). Divers must wear a suitable safety line and be able to communicate with the surface and in particular with their diving supervisor. The local emergency services should be advised by the diving contractor that diving is to take place.
Both divers and equipment require examination and testing. Divers should be trained to a recognized national or international standard, firstly and always for air diving and secondly for mixed-gas diving if this is to take place. They should be required to provide written evidence of successful completion of a diver training course. Divers should have an annual medical examination with a doctor experienced in hyperbaric medicine. Each diver should have a personal logbook in which a record of physicals and of his or her dives is kept. If a diver has been suspended from diving as a result of the physical, this also should be recorded in the logbook. A diver under suspension should not be allowed to dive or act as a standby diver. Divers should be asked by their diving supervisor if they are well, especially whether they have any respiratory illness, before being allowed to dive. Diving equipment, suits, belts, ropes, masks and cylinders and valves should be checked every day before use.
Satisfactory operation of cylinder and demand valves should be demonstrated by divers for their diving supervisor.
In the event of an accident or other reasons for the sudden ascent of a diver to the surface, he or she may experience the bends or be at risk of them and require to be recompressed. For this reason it is desirable that the whereabouts of a medical or other decompression chamber suitable for divers is located before diving starts. Those in charge of the chamber should be alerted to the fact that diving is taking place. Arrangements should be available for the rapid transport of divers requiring decompression.
Because of their training and equipment, plus all the backup required for safety, use of divers is very expensive, and yet the amount of time they are actually working on the riverbed may be limited. For these reasons there are temptations for diving contractors to use untrained or amateur divers or a diving team that is deficient in numbers and equipment. Only reputable diving contractors should be used for diving in construction, and particular care needs to be taken over the selection of divers who claim to have been trained in other countries where standards may be lower.
Caissons are rather like a large inverted saucepans whose rims sit on the bed of the harbour or river. Sometimes open caissons are used, which, as their name implies, have an open top. They are used on land to sink a shaft into soft ground. The bottom edge of the caisson is sharpened, workers excavate inside the caisson, and it sinks into the ground as soil is removed, thus creating the shaft. Similar open caissons are used in shallow water, but their depth may be extended by adding sections on top as the caisson sinks into the river or harbour bed. Open caissons rely on pumping to control the entry of water and soil into the base of the caisson. For deeper work still, a closed caisson will have to be used. Compressed air is pumped into it to displace the water, and workers are able to enter through an airlock, usually on top, and go down to work in air on that bed. Workers are able to work under water but are freed from the constraints of wearing diving equipment, and visibility is much better. The hazards in “pneumatic” caisson work are the bends and, as in all types of caisson including the simplest open caisson, drowning if water gets into the caisson through any structural failure or loss of air pressure. Because of the risk of entry of water, means of escape such as ladders up to the entry point should be available at all times in both open and pneumatic caissons.
Caissons should be inspected daily before they are used by someone competent and experienced in caisson work. Caissons may be raised and lowered as single units by heavy lifting equipment, or they may be constructed from components in the water. Construction of caissons should be under the supervision of a similarly competent person.
Tunnelling, when carried out in porous ground beneath water, may need to be done under compressed air. Driving tunnels for public transportation systems in city centres beneath rivers is a widespread practice, owing to lack of space above ground and environmental considerations. Compressed air working will be as limited as possible because of its danger and inefficiency.
Tunnels beneath water in porous ground will be lined with concrete or cast iron rings and grouted. But at the actual heading where the tunnel is being dug and in the short length where tunnel rings are being placed in position, there will not be a sufficiently water-tight surface for the work to proceed without some means of keeping out the water. Working under compressed air may still be used for the tunnel head and ring or segment placing part of the tunnel driving and lining process. Workers involved in driving the heading (i.e., on a TBM operating the rotating cutting head) or using hand tools, and those operating ring and segment placing equipment, will have to pass through an airlock. The rest of the now lined tunnel will not require to be compressed, and thus there will be easier transit of personnel and materials.
Tunnellers who have to work in compressed air face the same hazard of the bends as divers and caisson workers. The airlock giving access to the compressed-air workings should be supplemented by a second airlock through which workers pass at the end of the shift to be decompressed. If there is only a single airlock, this may create bottlenecks and also be dangerous. Hazards arise if workers are not decompressed sufficiently slowly at the end of their shift or if lack of airlock capacity holds up entry of vital equipment to the workings under pressure. Airlocks and decompression chambers should be under the supervision of a competent person experienced in compressed-air tunnelling and proper decompression.
Trenches are confined spaces usually dug to bury utilities or to place footings. Trenches are normally deeper than they are wide, as measured at the bottom, and are usually less than 6 m deep; they are also known as shallow excavations. A confined space is defined as a space that is large enough for a worker to enter and perform work, has limited means of entry and exit, and is not designed for continuous occupancy. Several ladders should be provided to enable workers to escape the trench.
Typically trenches are open only for minutes or hours. The walls of any trench will eventually collapse; it is merely a matter of time. Short-term apparent stability is a temptation for a contractor to send workers into a dangerous trench in hopes of rapid progress and financial gain. Death or serious injuries and mutilations can result.
In addition to being exposed to the possibility of collapsing trench walls, workers in trenches, can be harmed or killed by engulfment in water or sewage, exposure to hazardous gases or reduced oxygen, falls, falling equipment or materials, contact with severed electrical cables and improper rescue.
Cave-ins account for at least 2.5% of annual work-related deaths in the United States, for example. The average age of workers killed in trenches in the US is 33. Often a young person is trapped by a cave-in and other workers attempt a rescue. With failed rescue attempts, most of the dead are would-be rescuers. Emergency teams trained in trench rescue should be contacted immediately in the event of a cave-in.
Routine inspections of the trench walls and worker protection systems are essential. Inspections should occur daily before the start of work and after any occurrence—such as rainstorms, vibration or broken pipes—that may increase hazards. Following are descriptions of the hazards and how to prevent them.
Trench Wall Collapse
The main cause of deaths related to trenching is collapsed trench walls, which can crush or suffocate workers.
Trench walls may be weakened by activities outside but near a trench. Heavy loads must not be placed on the edge of the wall. Trenches should not be dug close to structures, such as buildings or railroads, because the trenching may undermine the structures and weaken the foundations, thus causing the structures and trench walls to collapse. Competent engineering assistance should be sought in the planning stages. Vehicles must not be permitted to approach too close to the sides of a trench; stop logs or soil berms should be in place to prevent vehicles from doing so.
Types of soil and environment
Proper selection of a worker protection system depends on soil and environmental conditions. Soil strength, the presence of water and vibration from equipment or nearby sources affect the stability of trench walls. Previously excavated soils never regain their strength. Accumulation of water in a trench, regardless of depth, signals the most dangerous situation.
The soil must be classified and the construction scene evaluated before an appropriate worker protection system is selected. A project safety and health plan should address unique conditions and hazards related to the project.
Soils can be divided into two main groups: cohesive and granular. Cohesive soils contain a minimum of 35% clay and will not break when rolled into threads 50 mm long and 3 mm in diameter and held by one end. With cohesive soils, trench walls will stand vertically for short periods of time. These soils are responsible for as many cave-in deaths as any other soil, because the soil appears stable and precautions often are not taken.
Granular soils consist of silt, sand, gravel or larger material. These soils exhibit apparent cohesion when wet (the sand-castle effect); the finer the particle, the greater the apparent cohesion. When submerged or dry, however, the coarser granular soils will immediately collapse to a stable angle, 30 to 45°, depending on their particle angularity or roundness.
Sloping prevents trench failure by removing the weight (of the soil) that can lead to trench instability. Sloping, including benching (sloping done in a series of steps), requires a wide opening at the top of a trench. The angle of a slope depends on the soil and environment, but slopes range from 0.75 horizontal: 1 vertical to 1.5 horizontal: 1 vertical. The slope of 1.5 horizontal: 1 vertical is set back 1.5 m on each side at the top for each meter of depth. Even the slightest slope is beneficial. However, the width requirements of slopes often make this approach impracticable on construction sites.
Shoring can be used for all conditions. A shore consists of an upright on each side of a trench, with braces in between (see figure 1). Shores help prevent trench wall collapse by exerting outward forces on a trench wall. Skip shores consist of vertical uprights and cross braces with soil arching between; they are used in clays, the most cohesive soils. Shores must be no more than 2 m apart from each other. Greater distances between cross braces can be achieved by using wales (or walings) to hold the uprights in place (see figure 2). Close sheeting is used in granular and weaker cohesive soils; the trench walls are covered entirely with sheeting (see figure 3). Sheeting can be made of wood, metal or fibreglass; steel trench sheets are common. Tight sheeting is used when flowing or seeping water is encountered. Tight sheeting prevents water from eroding and bringing soil particles into a trench. A shoring system must always be kept tight against the soil to prevent collapse. Braces can be of wood or of screw, hydraulic or pneumatic jacks. Wales can be of wood or metal.
Figure 1. Shores consist of uprights on each side of a trench with cross braces in between
Figure 2. Wales hold uprights in place, allowing greater distance between cross braces
Figure 3. Close sheeting is used in granular soils
Shields, or trench boxes, are large personal protective devices; they do not prevent trench wall collapse but protect workers who are inside. Shields are generally made of steel or aluminium and their size commonly ranges from approximately 1 m to 3 m high and 2 to 7 m long; many other sizes are available. Shields may be stacked on top of each other (figure 4). Guard systems must be in place against hazardous movements of shields in the event of a trench wall collapse. One way is to backfill on both sides of a shield.
Figure 4. Shields protect workers from trench wall collapse
New products are available that combine the qualities of a shore and a shield; some devices are useable in particularly hazardous ground. Shield-shore units can be used as static shields or can act as a shore by hydraulically or mechanically exerting forces on the trench wall. The smaller units are particularly useful when repairing breaks in utility pipes in city streets. Massive units with shield panels can be forced into the ground by mechanical or hydraulic means. Soil is then excavated from inside the shield.
Several steps are recommended to prevent engulfment by water or sewage in a trench. First, known utilities should be contacted before digging to learn where water (and other) pipes are located. Second, water valves that feed pipes into the trench should be closed. Cave-ins that break water mains or cause accumulations of water or sewage must be avoided. All utility pipes and other utility equipment need to be supported.
Deadly Gases and Fumes and Insufficient Oxygen
Harmful atmospheres can lead to worker death or injury resulting from a lack of oxygen, fire or explosion or toxic exposures. All trench atmospheres where abnormal conditions are present or suspected should be tested. This is especially true around buried garbage, vaults, fuel tanks, manholes, swamps, chemical processors and other facilities that can release deadly gases or fumes or deplete oxygen in the air. Construction equipment exhausts must be dispersed.
Air quality should be determined with instruments from outside the trench. This can be done by lowering a meter or its probe into the trench. The air in trenches should be tested in the following order. First, oxygen must be 19.5 to 23.5%. Second, flammability or explosibility must be no higher than 10% of the lower flammable or explosive limits (LFLs or LELs). Third, levels of potentially toxic substances—such as hydrogen sulphide —should be compared with published information. (In the US, one source is the National Institute for Occupational Safety and Health Pocket Guide to Chemical Hazards, which gives, permissible exposure limits (PELs)). If the atmosphere is normal, workers may enter. Ventilation may correct an abnormal atmosphere, but monitoring must continue. Sewers and similar spaces where the air is constantly changing usually require (or should require) a permit-entry procedure. Permit-entry procedures require full equipment and a three-person team: a supervisor, an attendant and an entrant.
Falls and Other Hazards
Falls into and within trenches can be prevented by providing safe and frequent means for entering and exiting a trench, safe walkways or bridges where workers or equipment are permitted or required to cross over trenches and barriers adequate to stop other workers or bystanders or equipment from approaching a trench.
Falling equipment or materials can cause death or injury through blows to the head and body, crushing and suffocation. The spoil pile should be kept at least 0.6 m from the edge of a trench, a barrier should be provided that will prevent soil and rock material from rolling into the trench. All other materials, such as pipes, must also be prevented from falling or rolling into a trench. Workers must not be permitted to work under suspended loads or loads handled by digging equipment.
All utilities should be marked prior to digging in order to prevent electrocution or severe burns caused by contact with live power lines. Equipment booms must not be operated near overhead power lines; if necessary, overhead lines must be grounded out or removed.
Often, one death or severe injury in a trench is compounded by a poorly thought-out rescue attempt. The victim and rescuers may become trapped and overcome by deadly gases, fumes or lack of oxygen; drowned; or mutilated by machines or rescue ropes. These compounded tragedies can be prevented by following a safety and health plan. Equipment such as air testing meters, water pumps and ventilators should be well-maintained, properly assembled and available on the job. Management should train and require workers to follow safe work practices and wear all necessary personal protective equipment.
Tools are particularly important in construction work. They are primarily used to put things together (e.g., hammers and nail guns) or to take them apart (e.g., jackhammers and saws). Tools are often classified as hand tools and power tools. Hand tools include all non-powered tools, such as hammers and pliers. Power tools are divided into classes, depending on the power source: electrical tools (powered by electricity), pneumatic tools (powered by compressed air), liquid-fuel tools (usually powered by gasoline), powder-actuated tools (usually powered by an explosive and operated like a gun) and hydraulic tools (powered by pressure from a liquid). Each type presents some unique safety problems.
Hand tools include a wide range of tools, from axes to wrenches. The primary hazard from hand tools is being struck by the tool or by a piece of the material being worked on. Eye injuries are very common from the use of hand tools, as a piece of wood or metal can fly off and lodge in the eye. Some of the major problems are using the wrong tool for the job or a tool that has not been properly maintained. The size of the tool is important: some women and men with relatively small hands have difficulty with large tools. Dull tools can make the work much harder, require more force and result in more injuries. A chisel with a mushroomed head might shatter on impact and send fragments flying. It is also important to have the proper work surface. Cutting material at an awkward angle can result in a loss of balance and an injury. In addition, hand tools can produce sparks that can ignite explosions if the work is being done around flammable liquids or vapours. In such cases, spark-resistant tools, such as those made from brass or aluminium, are needed.
Power tools, in general, are more dangerous than hand tools, because the power of the tool is increased. The biggest dangers from power tools are from accidental start-up and slipping or losing one’s balance during use. The power source itself can cause injuries or death, for example, through electrocution with electrical tools or gasoline explosions from liquid-fuel tools. Most power tools have a guard to protect the moving parts while the tool is not in operation. These guards need to be in working order and not overridden. A portable circular saw, for example, should have an upper guard covering the top half of the blade and a retractable lower guard which covers the teeth while the saw is not operating. The retractable guard should automatically return to cover the lower half of the blade when the tool is finished working. Power tools often also have safety switches that shut off the tool as soon as a switch is released. Other tools have catches that must be engaged before the tool can operate. One example is a fastening tool that must be pressed against the surface with a certain amount of pressure before it will fire.
One of the main hazards of electrical tools is the risk of electrocution. A frayed wire or a tool that does not have a ground (that directs the electrical circuit to the ground in an emergency) can result in electricity running through the body and death by electrocution. This can be prevented by using double-insulated tools (insulated wires in an insulated housing), grounded tools and ground-fault circuit interrupters (which will detect a leak of electricity from a wire and automatically shut off the tool); by never using electrical tools in damp or wet locations; and by wearing insulated gloves and safety footwear. Power cords have to be protected from abuse and damage.
Other types of power tools include powered abrasive-wheel tools, like grinding, cutting or buffing wheels, which present the risk of flying fragments coming off the wheel. The wheel should be tested to make sure it is not cracked and will not fly apart during use. It should spin freely on its spindle. The user should never stand directly in front of the wheel during start-up, in case it breaks. Eye protection is essential when using these tools.
Pneumatic tools include chippers, drills, hammers and sanders. Some pneumatic tools shoot fasteners at high speed and pressure into surfaces and, as a result, present the risk of shooting fasteners into the user or others. If the object being fastened is thin, the fastener may go through it and strike someone at a distance. These tools can also be noisy and cause hearing loss. Air hoses should be well connected before use to prevent them from disconnecting and whipping around. Air hoses should be protected from abuse and damage as well. Compressed-air guns should never be pointed at anyone or against oneself. Eye, face and hearing protection should be required. Jackhammer users should also wear foot protection in case these heavy tools are dropped.
Gas-powered tools present fuel explosion hazards, particularly during filling. They should be filled only after they have been shut down and allowed to cool off. Proper ventilation must be provided if they are being filled in a closed space. Using these tools in a closed space can also cause problems from carbon monoxide exposure.
Powder-actuated tools are like loaded guns and should be operated only by specially trained personnel. They should never be loaded until immediately before use and should never left loaded and unattended. Firing requires two motions: bringing the tool into position and pulling the trigger. Powder-actuated tools should require at least 5 pounds (2.3 kg) of pressure against the surface before they can be fired. These tools should not be used in explosive atmospheres. They should never be pointed at anyone and should be inspected before each use. These tools should have a safety shield at the end of the muzzle to prevent the release of flying fragments during firing. Defective tools should be taken out of service immediately and tagged or locked out to make sure no one else uses them until they are fixed. Powder-actuated fastening tools should not be fired into material where the fastener could pass through and hit somebody, nor should these tools be used near an edge where material might splinter and break off.
Hydraulic power tools should use a fire-resistant fluid and be operated under safe pressures. A jack should have a safety mechanism to prevent it from being jacked up too high and should display its load limit prominently. Jacks have to be set up on a level surface, centred, bear against a level surface and apply force evenly to be used safely.
In general, tools should be inspected before use, be well-maintained, be operated according to the manufacturer’s instructions and be operated with safety systems (e.g., guards). Users should have proper PPE, such as safety glasses.
Tools can present two other hazards that are often overlooked: vibration and sprains and strains. Power tools present a considerable vibration hazard to workers. The most well-known example is chain-saw vibration, which can result in “white-finger” disease, where the nerves and blood vessels in the hands are damaged. Other power tools can present hazardous exposures to vibration for construction workers. As much as possible, workers and contractors should purchase tools where vibration has been dampened or reduced; anti-vibration gloves have not been shown to solve this problem.
Poorly designed tools can also contribute to fatigue from awkward postures or grips, which, in turn, can also lead to accidents. Many tools are not designed for use by left-handed workers or individuals with small hands. Use of gloves can make it harder to grip a tool properly and requires tighter gripping of power tools, which can result in excessive fatigue. Use of tools by construction workers for repetitive jobs can also lead to cumulative trauma disorders, like carpal tunnel syndrome or tendinitis. Using the right tool for the job and choosing tools with the best design features that feel most comfortable in the hand while working can assist in avoiding these problems.
Construction work has undergone major changes. Once dependent upon craftsmanship with simple mechanical aids, the industry now relies largely on machines and equipment.
New equipment, machinery, materials and methods have contributed to the industry’s development. Around the middle of the 20th century, building cranes appeared, as did new materials like light-weight concrete. As time went on, the industry began using prefabricated construction units along with new techniques in the construction of buildings. Designers began to use computers. Thanks to such equipment as lifting devices, some of the work has become easier physically, but it has also become more complicated.
Instead of small, basic materials, such as bricks, tiles, board and light concrete, prefabricated construction units are commonly used today. Equipment has expanded from simple hand tools and transport facilities to complex machinery. Similarly, methods have changed, for instance, from wheelbarrowing to the pumping of concrete and from manual lifting of materials to the lifting of integrated elements with the assistance of cranes.
Innovations in equipment, machinery and materials can be expected to continue to appear.
European Community Directives Relating to Workers’ Health and Safety
In 1985, the European Community (EC) decided on a “New Approach to Technical Harmonization and Standards” in order to facilitate the free movement of goods. The New Approach directives are Community laws which set out essential requirements for health and safety that must be met before products may be supplied among member countries or imported to the Community. One example of a directive with a fixed level of demands is the Machine Directive (Council of the European Communities 1989). Products meeting the requirements of such a directive are marked and can be supplied anywhere in the EC. Similar systems exist for products covered by the Construction Products Directive (Council of the European Communities 1988).
Besides the directives with such a fixed level of demands, there are directives setting minimum criteria for workplace conditions. Community member states must meet these criteria or, if they exist, satisfy a more stringent safety level stipulated in their national regulations. Of specific relevance to construction work are the Directive on the Minimum Safety and Health Requirements for the Use of Work Equipment by Workers at Work (89/655/EEC) and the Directive on the Minimum Safety and Health Requirements at Temporary or Mobile Construction sites (92/57/EEC).
One of the types of construction equipment that frequently affects worker safety is scaffolding, the primary means of providing a work surface at elevations. Scaffolds are used in connection with construction, rebuilding, restoration, maintenance and servicing of buildings and other structures. Scaffold components may be used for other constructions such as support towers (which are not considered scaffolds) or for the erection of temporary structures such as grandstands (i.e., seating for spectators) and stages for concerts and other public presentations. Their use is associated with many occupational injuries, particularly those caused by falls from heights (see also the article “Lifts, escalators and hoists” in this chapter).
Types of scaffolds
Support scaffolds may be erected using vertical and horizontal tubing connected by loose couplers. Prefabricated scaffolds are assembled from parts manufactured in accord with standardized procedures that are permanently attached to fixation devices. There are several types: the traditional frame or modular type for building facades, mobile access towers (MATs), craftsmen scaffolds and suspended scaffolds.
Vertical adjustment of the scaffold
The working planes of a scaffold are normally stationary. Some scaffolds, however, have working planes that may be adjusted to different vertical positions; they may be suspended from wires that raise and lower them, or they may stand on the ground and be adjusted by hydraulic lifts or winches.
Erection of prefabricated facade scaffolds
The erection of prefabricated facade scaffolds should follow the following guidelines:
Earth-moving machinery is designed primarily to loosen, pick up, move, transport and distribute or grade rock or earth and is of great importance in construction, road-building and agricultural and industrial work (see figure 1). Properly used, these machines are versatile and can eliminate many of the risks associated with the manual handling of materials. This type of equipment is highly efficient and is used worldwide.
Figure 1. Mechanical excavation at a construction site in France
Earth-moving machines that are used in construction work and in road-building include tractor-dozers (bulldozers), loaders, backhoe loaders (figure 2), hydraulic excavators, dumpers, tractor-scrapers, graders, pipelayers, trenchers, landfill compactors and rope excavators.
Figure 2. Example of an articulated steer backhoe loader
The machine is versatile. It can be used for excavating, loading and lifting. The angling of the machine (articulation) enables it to be used in confined spaces.
Earth-moving machinery can endanger the operator and people working nearby. The following summary of the hazards associated with earth-moving machines is based on the European Community’s Standard EN 474-1 (European Committee for Standardization 1994). It points out the safety related factors to be considered when acquiring and using these machines.
The machine should provide safe access to the operator’s station and maintenance areas.
The minimum space available to the operator should allow for all manoeuvres necessary for the safe operation of the machinery without excessive fatigue. It should not be possible for the operator to have accidental contact with the wheels or tracks or the working equipment. The engine exhaust system should direct the exhaust gas away from the operator’s station.
A machine with an engine performance above 30 kW should be equipped with an operator’s cab, unless the machine is being operated where the year-round climate permits comfortable operation without a cab. Machines having an engine performance less than 30 kW should be fitted with a cab when intended for use where the air quality is poor. The airborne sound power level of excavators, dozers, loaders and backhoe loaders should be measured according to the international standard for measurement of airborne exterior noise emitted by earth-moving machinery (ISO 1985b).
The cab should protect the operator against foreseeable weather conditions. The interior of the cab should not present any sharp edges or acute angles that may injure the operator if he or she falls or is thrown against them. Pipes and hoses located inside the cab containing fluids that are dangerous because of their pressure or temperature should be reinforced and guarded. The cab should have an emergency exit separate from the usual doorway. The minimum height of the ceiling above the seat (i.e., seat-index point) depends on the size of the machine’s engine; for engines between 30 and 150 kW it should be 1,000 mm. All glass should be shatter-proof. The sound pressure level at the operator’s station should not exceed 85 dBA (ISO 1985c).
The design of the operator’s station should enable the operator to see the travelling and work areas of the machine, preferably without having to lean forward. Where the operator’s view is obscured, mirrors or remote cameras with a monitor visible to the operator should enable him or her to see the work area.
The front window and, if required, the rear window, should be fitted with motorized windscreen wipers and washers. Equipment for defogging and defrosting at least the front window of the cab should be provided.
Roll-over and falling object protection
Loaders, dozers, scrapers, graders, articulated steer dumpers and backhoe loaders with an engine performance of more than 15 kW should have a structure that will protect against roll-over. Machines intended for use where there is a risk of falling objects should be designed for and fitted with a structure that will protect the operator against falling material.
Machinery with provision for a seated operator should be fitted with an adjustable seat that keeps the operator in a stable position and allows him or her to control the machine under all expected operating conditions. Adjustments to accommodate to the operator’s size and weight should be easily made without the use of any tool.
The vibrations transmitted by the operator’s seat shall comply with the relevant international vibration standard (ISO 1982) for tractor-dozers, loaders and tractor-scrapers.
Controls and indicators
The main controls, indicators, hand levers, pedals, switches and so on should be selected, designed and arranged so that they are clearly defined, legibly labelled and within easy reach of the operator. Controls for machine components should be designed so that they cannot accidentally start or be moved, even if exposed to interference from radio or telecommunications equipment.
Pedals should have an appropriate size and shape, be surfaced with a non-skid tread to prevent slipping and be adequately spaced. To avoid confusion the machine should be designed to be operated like a motor vehicle, with pedals located in the same way (i.e., with the clutch on the left, the brake in the centre and the accelerator on the right).
Remote-controlled earth-moving machinery should be so designed that it stops automatically and remains immobile when controls are deactivated or the power supply to them is interrupted.
Earth-moving machinery should be equipped with:
Creep (drift away) from the stopping position, for whatever reason (e.g., internal leakage) other than action of the controls, should be such that it does not create a hazard to bystanders.
Steering and braking systems
The steering system should be such that the movement of the steering control shall correspond to the intended direction of steering. The steering system of rubber-tyred machinery with a travelling speed of more than 20 km/h should comply with the international steering system standard (ISO 1992).
Machinery should be fitted with service, secondary and parking brake systems that are efficient under all foreseeable conditions of service, load, speed, ground conditions and slope. The operator should be able to slow down and stop the machine by means of the service brake. In case it fails, a secondary brake should be provided. A mechanical parking device should be provided to keep the stopped machine from moving, and it should be capable of remaining in the applied position. The braking system should comply with the international braking system standard (ISO 1985a).
To permit night work or work in dusty conditions, earth-moving machines should be fitted with large enough and bright enough lights to adequately illuminate both the travelling and the work areas.
Earth-moving machinery, including components and attachments, should be designed and constructed to remain stable under anticipated operating conditions.
Devices intended to increase the stability of earth-moving machinery in working mode, such as outriggers and oscillating axle locking, should be fitted with interlocking devices which keep them in position, even in case of hydraulic hose failure.
Guards and covers
Guards and covers should be designed to be securely held in place. When access is rarely required, the guards should be fixed and fitted so that they are detachable only with tools or keys. Whenever possible, guards should remain hinged to the machine when open. Covers and guards should be fitted with a support system (springs or gas cylinders) to secure them in the opened position up to a wind speed of 8 m/s.
Electrical components and conductors should be installed in such a way as to avoid abrasion of wires and other wear and tear as well as exposure to dust and environmental conditions which can cause them to deteriorate.
Storage batteries should be provided with handles and be firmly attached in proper position while being easily disconnected and removed. Or, an easily accessible switch placed between the battery and the earth should allow the isolation of the battery from the rest of the electrical installation.
Tanks for fuel and hydraulic fluid
Tanks for fuel and hydraulic and other fluids should have means for relieving any internal pressure in case of opening and repair. They should have easy access for filling and be provided with lockable filler caps.
The floor and interior of the operator’s station should be made of fire-resistant materials. Machines with an engine performance exceeding 30 kW should have a built-in fire extinguisher system or a location for installing a fire extinguisher that is easily reached by the operator.
Machines should be designed and built so that lubrication and maintenance operations can be conducted safely, whenever possible with the engine stopped. When maintenance can be performed only with equipment in a raised position, the equipment should be mechanically secured. Special precautions such as erecting a shield or, at least, warning signs, must be taken if maintenance must be performed when the engine is running.
Each machine should bear, legibly and indelibly, the following information: the name and address of the manufacturer, mandatory marks, designation of series and type, the serial number (if any), the engine power (in kW), the mass of the most usual configuration (in kg) and, if appropriate, the maximum drawbar pull and maximum vertical load.
Other markings that may be appropriate include: conditions for use, mark of conformity (CE) and reference to instructions for installation, use and maintenance. The CE mark means that the machine meets the requirements of European Community directives relevant to the machine.
When the movement of a machine creates hazards not obvious to a casual spectator, warning signs should be affixed to the machine to warn against approaching it while it is in operation.
Verification of safety requirements
It is necessary to verify that safety requirements have been incorporated in the design and manufacture of an earth-moving machine. This should be achieved through a combination of measurement, visual examination, tests (where a method is prescribed) and assessment of the contents of the documentation that is required to be maintained by the manufacturer. The manufacturer’s documentation would include evidence that bought-in components, such as windscreens, have been manufactured as required.
A handbook giving instructions for operation and maintenance should be supplied and kept with the machine. It should be written in at least one of the official languages of the country in which the machine is to be used. It should describe in simple, readily understood terms the health and safety hazards that may be encountered (e.g., noise and hand-arm or whole-body vibration) and specify when personal protective equipment (PPE) is needed. A space intended for the safekeeping of the handbook should be provided in the operator’s station.
A service manual giving adequate information to enable trained service personnel to erect, repair and dismantle machinery with minimum risk should also be provided.
In addition to the above requirements for design, the instruction handbook should specify conditions that limit use of the machine (e.g., the machine should not travel at a greater angle of inclination than is recommended by the manufacturer). If the operator discovers faults, damage or excessive wear that may present a safety hazard, the operator should immediately inform the employer and shut down the machine until the necessary repairs are completed.
The machine must not attempt to lift a load heavier than specified in the capacity chart in the operating manual. The operator should check how the slings are attached to the load and to the lifting hook and if he or she finds that the load is not attached safely or has any concerns about its safe handling, the lift should not be attempted.
When a machine is moved with a suspended load, the load should be kept as near to the ground as possible to minimize potential instability, and the travel speed should be adjusted to prevailing ground conditions. A rapid change of speed should be avoided and care should be taken so the load does not begin to swing.
When the machine is in operation, no one should enter the work area without warning the operator. When the work requires individuals to remain within a machine’s work area, they should observe great care and avoid unnecessarily moving or remaining under a raised or suspended load. When someone is within the work area of the machine, the operator should be particularly careful and operate the machine only when that person is in the operator’s view or his or her location has been signalled to the operator. Similarly, for rotating machines, such as cranes and backhoes, the swing radius behind the machine should be kept clear. If a truck must be positioned for loading in a way such that falling debris might hit the driver’s cab, no one should remain in it, unless it is strong enough to withstand impact of the falling materials.
At the beginning of the shift, the operator should check brakes, locking devices, clutches, steering and the hydraulic system in addition to making a functional test without a load. When checking the brakes, the operator should make certain that the machine can be slowed down rapidly, then stopped and safely held in position.
Before leaving the machine at the end of the shift, the operator should place all operating controls in the neutral position, turn off the power supply and take all necessary precautions to prevent unauthorized operation of the machine. The operator should consider potential weather conditions that might affect the supporting surface, perhaps causing the machine to be frozen fast, tipped over or sunk, and take appropriate measures to prevent such occurrences.
Replacement parts and components, such as hydraulic hoses, should be in compliance with the specifications in the operating manual. Before attempting any replacement or repair work in the hydraulic or compressed air systems, the pressure should be relieved. The instructions and precautions issued by the manufacturer should be observed when, for instance, a working attachment is installed. PPE, such as a helmet and safety glasses, should be worn when repair and maintenance work are done.
Positioning a machine for work
When positioning a machine, the hazards of overturning, sliding and subsidence of the ground beneath it should be considered. When these appear to be present appropriate blocking of adequate strength and surface area should be provided to assure stability.
Overhead power lines
When operating a machine near overhead power lines, precautions against contact with the energized lines should be taken. In this connection, cooperation with the power distributor is advisable.
Underground pipes, cables and power lines
Prior to starting a project, the employer has the responsibility to determine if any underground power lines, cables or gas, water or sewer pipes are located within the work site and, if so, to determine and mark their precise location. Specific instructions for avoiding them must be given to the machine operator, for instance, through a “call before you dig” program.
Operation on roads with traffic
When a machine is operated on a road or other place open to public traffic, road signs, barriers and other safety arrangements appropriate for the traffic volume, vehicle speed and local road regulations should be used.
It is recommended that transport of a machine on a public highway should be executed by truck or trailer. The hazard of overturning should be considered when the machine is being loaded or unloaded, and it should be secured so that it will not shift while in transit.
Materials used in construction include asbestos, asphalt, brick and stone, cement, concrete, flooring, foil sealing agents, glass, glue, mineral wool and synthetic mineral fibres for insulation, paints and primers, plastic and rubber, steel and other metals, wallboard, gypsum and wood. Many of these are covered in other articles in this chapter or elsewhere in this Encyclopaedia.
The use of asbestos for new construction is prohibited in some countries but, almost inevitably, it will be encountered during the renovation or demolition of older buildings. Accordingly, stringent precautions are required to protect both the workers and the public against exposures to asbestos that was previously installed.
Bricks, concrete and stone
Bricks are made of fired clay and grouped into facing bricks and brick stones. They can be solid or designed with holes. Their physical properties depend on the clay used, any added materials, the method of manufacture and the incineration temperature. The higher the incineration temperature, the less absorbency the brick will exhibit.
Bricks, concrete and stone containing quartz can produce silica dust when cut, drilled or blasted. Unprotected exposures to crystalline silica can increase susceptibility to tuberculosis and cause silicosis, a disabling, chronic and potentially fatal lung disease.
Materials commonly used for interior flooring include stone, brick, floorboard, textile carpeting, linoleum and plastic. The installation of terrazzo, tile or wood flooring can expose a worker to dusts that can cause skin allergies or damage the nasal passages or lungs. In addition, the glues or adhesives used for installing tiles or carpeting often contain potentially toxic solvents.
Carpetlayers can damage their knees from kneeling and striking a “kicker” with the knee in stretching the carpeting to fit the space.
Glue is used to join materials through adhesion. Water-based glue contains a binding agent in water and hardens when water evaporates. Solvent glues harden when the solvent evaporates. Since the vapours can be harmful to health, they should not be used in very close or poorly ventilated areas. Glues consisting of components that harden when mixed can produce allergies.
Mineral wool and other insulation
The function of insulation in a building is to achieve thermal comfort and to reduce energy consumption. To achieve acceptable insulation, porous materials, such as mineral wool and synthetic mineral fibres, are used. Great care must be taken to avoid inhaling the fibres. Sharp fibres can even penetrate the skin and cause an annoying dermatitis.
Paints and primers
Paints are used to decorate the exterior and interior of the building, protect materials like steel and wood against corrosion or decay, make objects easier to clean and provide signals or road-markings.
Lead-based paints are now being avoided, but they may be encountered during the renovation or demolition of older structures, particularly those made of metal, such as bridges and viaducts. Inhaled or swallowed fumes or dusts can cause lead poisoning with kidney damage or permanent nervous system damage; they are particularly dangerous for children who may be exposed to lead dusts carried home on work clothes or shoes. Precautionary measures must be taken whenever lead-based paints are used or encountered.
Use of cadmium- and mercury-based paints is prohibited for use in most countries. Cadmium can cause kidney problems and some forms of cancer. Mercury can damage the nervous system.
Oil-based paints and primers contain solvents which may be potentially hazardous. To minimize solvent exposures, the use of water-based paints is recommended.
Plastic and rubber
Plastic and rubber, known as polymers, can be grouped into thermoplastic or thermosetting plastic and rubber. These materials are used in construction for tightening, insulation, coating, and for products like piping and fittings. Foil made of plastic or rubber is used for tightening and moisture-proof lining and may cause reactions in workers sensitized to these materials.
Steel, aluminium and copper
Steel is used in construction work as a supporting structure, in reinforcement rods, mechanical components and facing material. Steel may be carbon or alloy; stainless steel is a type of alloy. Important steel properties are its strength and toughness. Fracture toughness is important in order to avoid brittle fractures.
The properties of steel depends on its chemical composition and structure. Steel is heat-treated in order to release internal strain and to improve weldability, strength and fracture toughness.
Concrete can withstand considerable pressure, but reinforcement bars and nets are required for acceptable tensile strength. These bars typically have a considerable carbon content (0.40%).
Carbon steel or “mild” steel contains manganese, which, when released in fumes during welding, can cause a Parkinson’s disease-like syndrome, which can be a crippling nervous disorder. Aluminium and copper can also, under certain conditions, be harmful to health.
Stainless steels contain chromium, which increases corrosion resistance, and other alloy elements, such as nickel and molybdenum. But welding of stainless steel can expose workers to chromium and nickel fumes. Some forms of nickel can cause asthma or cancer; some forms of chromium can cause cancer and sinus problems and “nose holes” (erosion of the nasal septum).
Next to steel, aluminium is the most commonly used metal in construction, because the metal and its alloys are light, strong and corrosion-resistant.
Copper is one of the most important metals in engineering, because of its corrosion-resistance and high conductivity for electricity and heat. It is used in energized lines, as roof and wall coating and for piping. When used as a roof coating, copper salts in the rain runoff can be harmful to the immediate environment.
Wallboard and gypsum
Wallboard, often coated with asphalt or plastic, is used as a protective layer against water and wind and to prevent seepage of moisture through the building elements. Gypsum is crystallized calcium sulphate. Gypsum board consists of a sandwich of gypsum between two layers of cardboard; it is widely used as wall covering, and is fire-resistant.
Dust produced when cutting wallboard can lead to skin allergies or lung damage; carrying oversize or heavy board in awkward postures can cause musculoskeletal problems.
Wood is widely used for construction. It is important to use seasoned timber for construction work. For beams and roof trusses of considerable span, glue-laminated wood units are used. Measures are advisable to control wood dust, which, depending on the species, can cause a variety of ailments including cancer. Under certain conditions, wood dust can also be explosive.
A crane is a machine with a boom, primarily designed to raise and lower heavy loads. There are two basic crane types: mobile and stationary. Mobile cranes can be mounted on motor vehicles, boats or railroad cars. Stationary cranes can be of a tower type or mounted on overhead rails. Most cranes today are power driven, though some still operate manually. Their capacity, depending on the type and size, ranges from a few kilograms to hundreds of tonnes. Cranes are also used for pile driving, dredging, digging, demolition and personnel work platforms. Generally, a crane’s capacity is greater when the load is closer to its mast (centre of rotation) and less when the load is further away from its mast.
Accidents involving cranes are usually costly and spectacular. Injuries and fatalities involve not only workers, but sometimes innocent bystanders. Hazards exist in all facets of crane operation, including assembly, dismantling, travel and servicing. Some of the most common hazards involving cranes are:
Safe operation of a crane is the responsibility of all parties involved. Crane manufacturers are responsible for designing and manufacturing cranes that are stable and structurally sound. Cranes must be rated properly so that there are enough safeguards to prevent accidents caused by overloading and instability. Instruments such as load-limiting devices and angle and boom length indicators aid operators in the safe operation of a crane. (Powerline sensory devices have proved to be unreliable.) Every crane should have a reliable, efficient, automatic safe- load indicator. In addition, crane manufacturers must make accommodations in the design that facilitate safe access for servicing and safe operation. Hazards can be reduced by clear design of control panels, providing a chart at the operator’s fingertips that specifies load configurations, handrails, non-glare windows, windows that extend to the cab floor, comfortable seats and both noise and thermal insulation. In some climates, heated and air-conditioned cabs contribute to the worker’s comfort and reduce fatigue.
Crane owners are responsible for keeping their machines in good condition by ensuring regular inspection and proper maintenance and employing competent operators. Crane owners must be knowledgeable so that they can recommend the best machine for a particular job. A crane assigned to a project should have the capacity to handle the heaviest load it must carry. The crane should be fully inspected by a competent person before being assigned to a project, and then daily and periodically (as suggested by the manufacturer), with a maintenance record kept. Ventilation should be provided to remove or dilute engine exhaust from cranes working in enclosed areas. Hearing protection, when necessary, should be provided. Site supervisors must plan ahead. With proper planning operating near overhead powerlines can be avoided. When work must be done near high-voltage power lines, clearance requirements should be followed (see table 1). When working near powerlines cannot be avoided, the line should either be de-energized or insulated.
Table 1. Required clearance for normal voltage in operation near high-voltage power lines
|Normal voltage in kilovolts
(phase to phase)
|Minimum required clearance in metres
|Up to 50||3.1 (10)|
|From 50 to 200||4.6 (15)|
|From 200 to 350||6.1 (20)|
|From 350 to 500||7.6 (25)|
|From 500 to 750||10.7 (35)|
|From 750 to 1,000||13.7 (45)|
* Meters have been converted from recommendations in feet.
Source: ASME 1994.
Signallers should be used to aid the operator near the limit of approach around powerlines. The ground, including access in and around the site, must have the ability to bear the weight of the crane and the load it is lifting. If possible, the crane operating area should be roped off to prevent injuries from overhead lifting. A signaller must be used when the operator cannot see the load clearly. The crane operator and the signaller must be trained and competent in hand signals and other aspects of the job. Proper rigging attachments must be supplied so that riggers can secure the load from falling or slipping. The rigging crew must be trained in the attachment and dismantling of loads. Good communication is vital in safe crane operations. The operator must carefully follow the manufacturer’s recommended procedures when assembling and disassembling the boom before operating the crane. All safety features and warning devices should be in working order and should not be disconnected. The crane must be levelled and be operated according to the crane load chart. Outriggers must be fully extended or set according to manufacturers’ recommendations. Overloading can be prevented by the operator’s knowing the weight to be lifted in advance and by using load-limiting devices as well as other indicators. The operator should always use sound craning practices. All loads must be fully secured before they are lifted. Movement with a load must be slow; the boom should never be extended or lowered so that it compromises the stability of the crane. Cranes should not be operated when visibility is poor or when the wind can cause the operator to lose control of the load.
Standards and Legislation
There are numerous written standards or guidelines for recommended manufacturing and operating practices. Some are based on design principles, some on performance. Subjects covered in these standards include methods of testing various safety devices; design, construction and characteristics of the cranes; inspection, testing, maintenance and operation procedures; recommended equipment and control lay-out. These standards form the basis of government and company health and safety regulations and operator training.
An elevator (lift) is a permanent lifting installation serving two or more defined landing levels, comprising an enclosed space, or car, whose dimensions and means of construction clearly permit the access of people, and which runs between rigid vertical guides. A lift, therefore, is a vehicle for raising and lowering people and/or goods from one floor to another floor within a building directly (single push-button control) or with intermediate stops (collective control).
A second category is the service lift (dumb waiter), a permanent lifting installation serving defined levels, but with a car that is too small to transport people. Service lifts transport foods and supplies in hotels and hospitals, books in libraries, mail in office buildings and so on. Generally, the floor area of such a car does not exceed 1 m2, its depth 1 m, and its height 1.20 m.
Elevators are driven directly by an electric motor (electric lifts; see figure 1) or indirectly, through the movement of a liquid under pressure generated by a pump driven by an electric motor (hydraulic lifts).
Figure 1. A cut-away view of an elevator installation showing the essential components
Electric lifts are almost exclusively driven by traction machines, geared or gearless, depending on car speed. The designation “traction” means that the power from an electric motor is transmitted to the multiple rope suspension of the car and a counterweight by friction between the specially shaped grooves of the driving or traction sheave of the machine and the ropes.
Hydraulic lifts have become widely used since the 1970s for the transport of goods and passengers, usually for a height not exceeding six floors. Hydraulic oil is used as pressure fluid. The direct-acting system with a ram supporting and moving the car is the simplest one.
Technical Committee 178 of the ISO has drafted standards for: loads and speeds up to 2.50 m/s; car and hoistway dimensions to accommodate passengers and goods; bed and service lifts for residential buildings, offices, hotels, hospitals and nursing homes; control devices, signals and additional accessories; and selection and planning of lifts in residential buildings. Each building should be provided with at least one lift accessible to handicapped people in wheelchairs. The Association française de normalisation (AFNOR) is in charge of the Secretariat of this Technical Committee.
General safety requirements
Every industrialized country has a safety code drawn up and kept up to date by a national standards committee. Since this work was started in the 1920s, the various codes have gradually been made more similar, and differences now are generally not fundamental. Large manufacturing firms produce units that comply with the codes.
In the 1970s the ILO, in close cooperation with the International Committee for the Reglementation of Lifts (CIRA), published a code of practice for the construction and installation of lifts and service lifts and, a few years later, for escalators. These directives are intended as a guide for countries engaged in the drafting or modification of safety rules. A standardized set of safety rules for electric and hydraulic lifts, service lifts, escalators and passenger conveyors, the object being the elimination of technical barriers to trade among the member countries of the European Community, is also under the purview of the European Committee for Standardization (CEN). The American National Standards Institute (ANSI) has devised a safety code for lifts and escalators.
Safety rules are aimed at several types of possible accidents with lifts: shearing, crushing, falling, impact, trapping, fire, electric shock, damage to material, accidents due to wear, and accidents due to corrosion. People to be safeguarded are: users, maintenance and inspection personnel and people outside the hoistway and the machine room. Objects to be safeguarded are: loads in the car, components of the lift installation and the building.
Committees drawing up safety rules have to assume that all components are correctly designed, are of sound mechanical and electrical construction, are made of material of adequate strength and suitable quality and are free from defects. Potential imprudent acts of users have to be taken into account.
Shearing is prevented by providing adequate clearances between moving components and between moving and fixed parts. Crushing is prevented by providing sufficient headroom at the top of the hoistway between the roof of the car in its highest position and the top of the shaft and a clear space in the pit where someone can remain safely when the car is in its lowest position. These spaces are assured by buffers or stops.
Protection against falling down the hoistway is obtained by solid landing doors and an automatic cut off that prevents movement of the cab until the doors are fully closed and locked. Landing doors of the power-operated sliding type are preferred for passenger lifts.
Impact is limited by restraining the kinetic energy of closing power-operated doors; trapping of passengers in a stalled car is prevented by providing an emergency unlocking device on the doors and a means for specially trained personnel to open them and extricate the passengers.
Overloading of a car is prevented by a strict ratio between the rated load and the net floor area of the car. Doors are required on all the cars passenger lifts to keep passengers from being trapped in the space between the car sill and the hoistway or the landing doors. Car sills must be fitted with a toe guard of a height of not less than 0.75 m to prevent accidents, as shown in figure 2. Cars have to be provided with safety gear capable of stopping and holding a fully loaded car in the event of overspeed or failure of the suspension. The gear is operated by an overspeed governor driven by the car by means of a rope (see figure 1). As passengers stand upright and move in a vertical direction, the retardation during the operation of the safety device should lie between 0.2 and 1.0 g (m/s2) to guard against injuries (g = standard acceleration of free fall).
Figure 2. Layout of the toe guard on the car sill to prevent trapping
Depending on national legislation, lifts intended mainly for the transport of goods, vehicles and motor cars accompanied by authorized and instructed users may have one or two opposite car entrances not provided with car doors, under the condition that the rated speed does not exceed 0.63 m/s, the car depth is not less than 1.50 m and the wall of the hoistway facing the entrance, including the landing doors, is flush and smooth. On heavy-duty freight elevators (goods lifts), the landing doors are usually vertical bi-parting power-operated doors, which usually do not meet these conditions. In such a case, the required car door is a vertically sliding mesh gate. The clear width of the lift car and the landing doors must be the same to avoid damage to panels on the lift car by fork trucks or other vehicles entering or leaving the lift. The whole design of such a lift has to take account of the load, the weight of the handling equipment and the heavy forces involved in running, stopping and reversing these vehicles. The lift car guides require special reinforcement. When the transport of people is permitted, the number allowed should correspond to the maximum available area of the car floor. For example, the car floor area of a lift for a rated load of 2,500 kg should be 5 m2, corresponding to 33 persons. Loading and accompanying a load must be done with great care. Figure 3 shows a faulty situation.
Figure 3. Example of dangerous loading of a freight elevator (goods-lift).
All modern lifts are push-button and computer controlled, the car switch system operated by an attendant having been abandoned.
Single lifts and those grouped in two- to eight-car arrangements are usually equipped with collective controls which are interconnected in the case of multiple installations. The main feature of collective controls is that calls can be given at any moment, whether the car is moving or standstill and whether the landing doors are open or closed. Landing and car calls are collected and stored until answered. Regardless of the sequence in which they are received, calls are answered in the order that most efficiently operates the system.
Examinations and tests
Before a lift is put into service, it should be examined and tested by an organization approved by the public authorities to establish the lift’s conformity with the safety rules in the country where it has been installed. A technical dossier should be submitted to the inspector by the manufacturers. The elements to be examined and tested and the way the tests should be run are listed in the safety code. Specific tests by an approved laboratory are required for: locking devices, landing doors (possibly including fire tests), safety gear, overspeed governors and oil buffers. Certificates of the corresponding components used in the installation should be included in the register. After a lift is put into service, periodic safety examinations should be conducted, with the intervals depending on traffic volume. These tests are intended to ensure compliance with the code and the proper operation of all safety devices. Components that do not function in normal service, such as the safety gear and buffers, should be tested with a car empty and at reduced speed to prevent excessive wear and stresses that can impair the safety of a lift.
Maintenance and inspection
A lift and its components should be inspected and maintained in good and safe working order at regular intervals by competent technicians who have obtained skill and a thorough knowledge of the mechanical and electrical details of the lift and the safety rules under the guidance of a qualified instructor. Preferably the technician is employed by the supplier or erector of the lift. Normally a technician is responsible for a specific number of lifts. Maintenance involves routine servicing such as adjustment and cleaning, lubrication of moving parts, preventive servicing to anticipate possible problems, emergency visits in the case of breakdowns and major repairs, which are usually done after consultation with a supervisor. The overriding safety hazard, however, is fire. Because of the risk that a lit cigarette or other burning object might fall into the crack between the car sill and the hoistway and ignite lubricating grease in the hoistway or debris at the bottom, the hoistway should regularly be cleaned out. All systems should be at zero energy level before maintenance work is begun. In single-unit buildings, before any work is started, notices should be posted at each landing indicating that the lift is out of service.
For preventive maintenance, careful visual inspection and checks of free movement, the condition of contacts and proper operation of the equipment are generally sufficient. The hoistway equipment is inspected from the top of the car. An inspection control is provided on the car roof comprising: a bi-stable switch to bring it into operation and to neutralize the normal control, including the operation of power-operated doors. Up and down constant pressure buttons allow movement of the car at reduced speed (not exceeding 0.63 m/s). The inspection operation must remain dependent on the safety devices (closed and locked doors and so on) and it should not be possible to overrun the limits of normal travel.
A stop switch on the inspection control station prevents unexpected movement of the car. The safest direction of travel is down. The technician must be in a safe position to observe the work environment when moving the car and possess the appropriate inspection devices. The technician must have a firm hold when the car is in motion. Before leaving, the technician must report to the person in charge of the lift.
An escalator is a continuous moving, inclined stairway which conveys passengers upward and downward. Escalators are used in commercial buildings, department stores and railway and underground stations, to guide a stream of people in a confined route from one level to another.
General safety requirements
Escalators consist of a continuous chain of steps moved by a motor-driven machine by means of two roller chains, one at each side. The steps are guided by rollers on tracks which keep the step treads horizontal in the usable area. At the entrance and exit, guides ensure that over a distance of 0.80 to 1.10 m, depending on the speed and rise of the escalator, some steps form a horizontal flat surface. Step dimensions and construction are shown in figure 4. On the top of each balustrade, a handrail should be provided at a height of 0.85 to 1.10 m above the nose of the steps running parallel to the steps at substantially the same speed. The handrail at each extremity of the escalator, where the steps move horizontally, should extend at least 0.30 m beyond the landing plate and the newel including the handrail at least 0.60 m beyond (see figure 5). The handrail should enter the newel at a low point above the floor, and a guard should be installed with a safety switch to stop the escalator if fingers or hands are trapped at this point. Other risks of injury to users are formed by the clearances necessary between the side of the steps and the balustrades, between steps and combs and between treads and step risers, the latter more particularly in the upward direction at the curvature where a relative movement between consecutive steps occurs. The cleating and smoothness of the risers should prevent this risk.
Figure 4. Escalator step unit 1 (X: Height to next step (not greater than 0.24m); Y: Depth (at least 0.38m); Z: Width (between 0.58 and 1.10m); Δ: Grooved step tread; Φ: Cleated step riser)
Figure 5. Escalator step unit 2
People may ride with their shoes sliding against the balustrade, which can cause trapping at the points where the steps straighten out. Clearly legible signs and notices, preferably pictographs, should warn and instruct users. A sign should instruct adults to hold the hands of children, who may not be able to reach the handrail, and that children should stand at all times. Both ends of an escalator should be barricaded when it is out of service.
The incline of an escalator should not exceed 30°, though it may be increased to 35° if the vertical rise is 6 m or less and the speed along the incline is limited to 0.50 m/s. Machine rooms and driving and return stations should be easily accessible to specially-trained maintenance and inspection personnel only. These spaces can lie inside the truss or be separate. The clear height should be 1.80 m with covers, if any, opened and the space should be sufficient to ensure safe working conditions. The clear height above the steps at all points should be not less than 2.30 m.
The starting, stopping or reversal of movement of an escalator should be effected by authorized people only. If the country code permits operating a system that starts automatically when a passenger moves past an electric sensor, the escalator should be in operation before the user reaches the comb. Escalators should be equipped with an inspection control system for operation during maintenance and inspection.
Maintenance and inspection
Maintenance and inspection along the lines described above for lifts are usually required by authorities. A technical dossier should be available listing the main calculation data of the supporting structure, steps, step driving components, general data, layout drawings, schematic wiring diagrams and instructions. Before an escalator is put into service, it should be examined by a person or organization approved by the public authorities; subsequently periodic inspections at given intervals are needed.
Moving Walkways (Passenger Conveyors)
A passenger conveyor, or power-driven continuous moving walkway, may be used for the conveyance of passengers between two points at the same or at different levels. Passenger conveyors are used to transport a great number of people in airports from the main station to the gates and back and in department stores and supermarkets. When the conveyors are horizontal, baby carriages, pushcarts and wheelchairs, luggage and food trolleys can be carried without risk, but on inclined conveyors these vehicles, if rather heavy, should be used only if they lock into place automatically. The ramp consists of metal pallets, similar to the step treads of escalators but longer, or rubber belt. The pallets must be grooved in the direction of travel, and combs should be placed at each end. The angle of inclination should not exceed 12° or more than 6° at the landings. The pallets and belt should move horizontally over a distance of not less than 0.40 m before entering the landing. The walkway runs between balustrades that are topped with a moving handrail that travels at substantially the same speed. The speed should not exceed 0.75 m/s unless the movement is horizontal, in which case 0.90 m/s is permitted provided the width does not exceed 1.10 m.
The safety requirements for passenger conveyors are generally similar to those for escalators and should be included in the same code.
Building hoists are temporary installations used on construction sites for the transport of persons and materials. Each hoist is a guided car and should be operated by an attendant inside the car. In recent years, rack and pinion design has enabled the use of building hoists for efficient movement along radio towers or very tall smoke stacks for servicing. No one should ride a material hoist, except for inspection or maintenance.
The standards of safety vary considerably. In a few cases, these hoists are installed with the same standard of safety as permanent goods and passenger lifts in buildings, except that the hoistway is enclosed by strong wire mesh instead of solid materials to reduce the wind load. Strict regulations are needed although they need not be as strict as for passenger lifts; many countries have special regulations for these building hoists. However, in many cases the standard of safety is low, the construction poor, the hoists driven by a diesel engine winch and the car suspended by only a single steel wire rope. A building hoist should be driven by electric motors to ensure that the speed is kept within safe limits. The car should be enclosed and be provided with car entrance protections. Hoistway openings at the landings should be fitted with doors that are solid up to a height of 1 m from the floor, the upper part in wire mesh of maximum 10 x 10 mm aperture. Sills of landing doors and cars should have suitable toe guards. Cars should be provided with safety gear. One common type of accident results when workers travel on a platform hoist designed only for carrying goods, which do not have side walls or gates to keep the workers from striking a part of the scaffolding or from falling off the platform during the journey. A belt lift consists of steps on a moving vertical belt. A rider is at risk of being carried over the top, being unable to make an emergency stop, striking his or her head or shoulders on the edge of a floor opening, jumping on or off after the step has passed the floor level or being unable to reach the landing because of power failure or the belt’s stopping. Accordingly, such a lift should be used only by specially trained personnel employed by the building owner or a designee.
Generally, the hoistway for any lift extends over the full height of a building and interconnects the floors. A fire or the smoke from a fire breaking out in the lower part of a building may spread up the hoistway to other floors and, under certain circumstances, the well or hoistway may intensify a fire because of a chimney effect. Therefore, a hoistway should not form part of a building’s ventilation system. The hoistway should be totally enclosed by solid walls of non-combustible material that would not give off harmful fumes in case of a fire. A vent should be provided at the top of the lift hoistway or in the machine room above it to allow smoke to escape to open air.
Like the hoistway, the entrance doors should be fire resistant. Requirements are usually laid down in national building regulations and vary according to countries and conditions. Landing doors cannot be made smokeproof if they are to operate reliably.
No matter how tall the building, passengers should not use lifts in case of fire, because of the risks of the lift stopping at a floor in the fire zone and of passengers being trapped in the car in the event of failure of the electrical supply. In general, one lift that serves all floors is designated as a lift for firefighters that can be put at their disposal by means of a switch or special key on the main floor. The capacity, speed and car dimensions of the firefighters’ lift have to meet certain specifications. When firefighters use lifts, the normal operational controls are overridden.
The construction, maintenance and refinishing of elevator interiors, installation of carpeting and cleaning of the elevator (inside or out) may involve the use of volatile organic solvents, mastics or glues, which can present a risk to the central nervous system, as well as a fire hazard. Although these materials are used on other metal surfaces, including staircases and doors, the hazard is severe with elevators because of their small space, in which vapour concentrations can become excessive. The use of solvents on the outside of an elevator car can also be risky, again because of limited air flow, particularly in a blind hoistway, where venting may be impeded. (A blind hoistway is one without an exit door, usually extending for several floors between two destinations; where a group of elevators serves floors 20 and above, a blind hoistway would extend between floors 1 and 20.)
Lifts and Health
While lifts and hoists involve hazards, their use can also help reduce fatigue or serious muscle injury due to manual handling, and they can reduce labour costs, especially in building construction work in some developing countries. On some such sites where no lifts are used, workers have to carry heavy loads of bricks and other building materials up inclined runways numerous floors high in hot, humid weather.
Cement is a hydraulic bonding agent used in building construction and civil engineering. It is a fine powder obtained by grinding the clinker of a clay and limestone mixture calcined at high temperatures. When water is added to cement it becomes a slurry that gradually hardens to a stone-like consistency. It can be mixed with sand and gravel (coarse aggregates) to form mortar and concrete.
There are two types of cement: natural and artificial. The natural cements are obtained from natural materials having a cement-like structure and require only calcining and grinding to yield hydraulic cement powder. Artificial cements are available in large and increasing numbers. Each type has a different composition and mechanical structure and has specific merits and uses. Artificial cements may be classified as portland cement (named after the town of Portland in the United Kingdom) and aluminous cement.
The portland process, which accounts for by far the largest part of world cement production, is illustrated in figure 1. It comprises two stages: clinker manufacture and clinker grinding. The raw materials used for clinker manufacture are calcareous materials such as limestone and argillaceous materials such as clay. The raw materials are blended and ground either dry (dry process) or in water (wet process). The pulverised mixture is calcined either in vertical or rotary-inclined kilns at a temperature ranging from 1,400 to 1,450°C. On leaving the kiln, the clinker is cooled rapidly to prevent the conversion of tricalcium silicate, the main ingredient of portland cement, into bicalcium silicate and calcium oxide.
Figure 1. The manufacture of cement
The lumps of cooled clinker are often mixed with gypsum and various other additives which control the setting time and other properties of the mixture in use. In this way it is possible to obtain a wide range of different cements such as normal portland cement, rapid-setting cement, hydraulic cement, metallurgical cement, trass cement, hydrophobic cement, maritime cement, cements for oil and gas wells, cements for highways or dams, expansive cement, magnesium cement and so on. Finally, the clinker is ground in a mill, screened and stored in silos ready for packaging and shipping. The chemical composition of normal portland cement is:
Aluminous cement produces mortar or concrete with high initial strength. It is made from a mixture of limestone and clay with a high aluminium oxide content (without extenders) which is calcined at about 1,400°C. The chemical composition of aluminous cement is approximately:
Fuel shortages lead to the increased production of natural cements, especially those using tuff (volcanic ash). If necessary, this is calcined at 1,200°C, instead of 1,400 to 1,450°C as required for portland. The tuff may contain 70 to 80% amorphous free silica and 5 to 10% quartz. With calcination the amorphous silica is partially transformed to tridimite and crystobalite.
Cement is used as a binding agent in mortar and concrete —a mixture of cement, gravel and sand. By varying the processing method or by including additives, different types of concrete may be obtained using a single type of cement (e.g., normal, clay, bituminous, asphalt tar, rapid-setting, foamed, waterproof, microporous, reinforced, stressed, centrifuged concrete and so on).
In the quarries from which the clay, limestone and gypsum for cement are extracted, workers are exposed to the hazards of climatic conditions, dusts produced during drilling and crushing, explosions and falls of rock and earth. Road transport accidents occur during haulage to the cement works.
During cement processing, the main hazard is dust. In the past, dust levels ranging from 26 to 114 mg/m3 have been recorded in quarries and cement works. In individual processes the following dust levels were reported: clay extraction—41.4 mg/m3; raw materials crushing and milling—79.8 mg/m3; sieving— 384 mg/m3; clinker grinding—140 mg/m3; cement packing— 256.6 mg/m3; and loading, etc.—179 mg/m3. In modern factories using the wet process, 15 to 20 mg dust/m3 air are occasionally the upper short-time values. The air pollution in the neighbourhood of cement factories is around 5 to 10% of the old values, thanks in particular to the widespread use of electrostatic filters. The free silica content of the dust usually varies between the level in raw material (clay may contain fine particulate quartz, and sand may be added) and that of the clinker or the cement, from which all the free silica will normally have been eliminated.
Other hazards encountered in cement works include high ambient temperatures, especially near furnace doors and on furnace platforms, radiant heat and high noise levels (120 dB) in the vicinity of the ball mills. Carbon monoxide concentrations ranging from trace quantities up to 50 ppm have been found near limestone kilns.
Other hazardous conditions encountered in cement industry workers include diseases of the respiratory system, digestive disorders, skin diseases, rheumatic and nervous conditions and hearing and visual disorders.
Respiratory tract diseases
Respiratory tract disorders are the most important group of occupational diseases in the cement industry and are the result of inhalation of airborne dust and the effects of macroclimatic and microclimatic conditions in the workplace environment. Chronic bronchitis, often associated with emphysema, has been reported as the most frequent respiratory disease.
Normal portland cement does not cause silicosis because of the absence of free silica. However, workers engaged in cement production may be exposed to raw materials which present great variations in free silica content. Acid-resistant cements used for refractory plates, bricks and dust contain high amounts of free silica, and exposure to them involves a definite risk of silicosis.
Cement pneumoconiosis has been described as a benign pinhead or reticular pneumoconiosis, which may appear after prolonged exposure, and presents a very slow progression. However, a few cases of severe pneumoconiosis have also been observed, most likely following exposure to materials other than clay and portland cement.
Some cements also contain varying amounts of diatomaceous earth and tuff. It is reported that when heated, diatomaceous earth becomes more toxic due to the transformation of the amorphous silica into cristobalite, a crystalline substance even more pathogenic than quartz. Concomitant tuberculosis may complicate the course of the cement pneumoconiosis.
Attention has been drawn to the apparently high incidence of gastroduodenal ulcers in the cement industry. Examination of 269 cement plant workers revealed 13 cases of gastroduodenal ulcer (4.8%). Subsequently, gastric ulcers were induced in both guinea pigs and a dog fed on cement dust. However, a study at a cement works showed a sickness absence rate of 1.48 to 2.69% due to gastroduodenal ulcers. Since ulcers may pass through an acute phase several times a year, these figures are not excessive when compared with those for other occupations.
Skin diseases are widely reported in the literature and have been said to account for about 25% and more of all the occupational skin diseases. Various forms have been observed, including inclusions in the skin, periungal erosions, diffuse eczematous lesions and cutaneous infections (furuncles, abscesses and panaritiums). However, these are more frequent among cement users (e.g., bricklayers and masons) than among cement manufacturing plant workers.
As early as 1947 it was suggested that cement eczema might be due to the presence in the cement of hexavalent chromium (detected by the chromium solution test). The chromium salts probably enter the dermal papillae, combine with proteins and produce a sensitization of an allergic nature. Since the raw materials used for cement manufacture do not usually contain chromium, the following have been listed as the possible sources of the chromium in cement: volcanic rock, the abrasion of the refractory lining of the kiln, the steel balls used in the grinding mills and the different tools used for crushing and grinding the raw materials and the clinker. Sensitization to chromium may be the leading cause of nickel and cobalt sensitivity. The high alkalinity of cement is considered an important factor in cement dermatoses.
Rheumatic and nervous disorders
The wide variations in macroclimatic and microclimatic conditions encountered in the cement industry have been associated with the appearance of various disorders of the locomotor system (e.g., arthritis, rheumatism, spondylitis and various muscular pains) and the peripheral nervous system (e.g., back pain, neuralgia and radiculitis of the sciatic nerves).
Hearing and vision disorders
Moderate cochlear hypoacusia in workers in a cement mill has been reported. The main eye disease is conjunctivitis, which normally requires only ambulatory medical care.
Accidents in quarries are due in most cases to falls of earth or rock, or they occur during transportation. In cement works the main types of accidental injuries are bruises, cuts and abrasions which occur during manual handling work.
Safety and health measures
A basic requirement in the prevention of dust hazards in the cement industry is a precise knowledge of the composition and, especially, of the free silica content of all the materials used. Knowledge of the exact composition of newly-developed types of cement is particularly important.
In quarries, excavators should be equipped with closed cabins and ventilation to ensure a pure air supply, and dust suppression measures should be implemented during drilling and crushing. The possibility of poisoning due to carbon monoxide and nitrous gases released during blasting may be countered by ensuring that workers are at a suitable distance during shotfiring and do not return to the blasting point until all fumes have cleared. Suitable protective clothing may be necessary to protect workers against inclement weather.
All dusty processes in cement works (grinding, sieving, transfer by conveyor belts) should be equipped with adequate ventilation systems, and conveyor belts carrying cement or raw materials should be enclosed, with special precautions being taken at conveyor transfer points. Good ventilation is also required on the clinker cooling platform, for clinker grinding and in cement packing plants.
The most difficult dust control problem is that of the clinker kiln stacks, which are usually fitted with electrostatic filters, preceded by bag or other filters. Electrostatic filters may be used also for the sieving and packing processes, where they must be combined with other methods for air pollution control. Ground clinker should be conveyed in enclosed screw conveyors.
Hot work points should be equipped with cold air showers, and adequate thermal screening should be provided. Repairs on clinker kilns should not be undertaken until the kiln has cooled adequately, and then only by young, healthy workers. These workers should be kept under medical supervision to check their cardiac, respiratory and sweat function and prevent the occurrence of thermal shock. Persons working in hot environments should be supplied with salted drinks when appropriate.
Skin disease prevention measures should include the provision of shower baths and barrier creams for use after showering. Desensitization treatment may be applied in cases of eczema: after removal from cement exposure for 3 to 6 months to allow healing, 2 drops of 1:10,000 aqueous potassium dichromate solution is applied to the skin for 5 minutes, 2 to 3 times per week. In the absence of local or general reaction, contact time is normally increased to 15 minutes, followed by an increase in the strength of the solution. This desensitization procedure can also be applied in cases of sensitivity to cobalt, nickel and manganese. It has been found that chrome dermatitis—and even chrome poisoning—may be prevented and treated with ascorbic acid. The mechanism for the inactivation of hexavalent chromium by ascorbic acid involves reduction to trivalent chromium, which has a low toxicity, and subsequent complex formation of the trivalent species.
Concrete and Reinforced Concrete Work
To produce concrete, aggregates, such as gravel and sand, are mixed with cement and water in motor-driven horizontal or vertical mixers of various capacities installed at the construction site, but sometimes it is more economical to have ready-mixed concrete delivered and discharged into a silo on the site. For this purpose concrete mixing stations are installed in the periphery of towns or near gravel pits. Special rotary-drum lorries are used to avoid separation of the mixed constituents of the concrete, which would lower the strength of concrete structures.
Tower cranes or hoists are used to transport the ready-mixed concrete from the mixer or silo to the framework. The size and height of certain structures may also require the use of concrete pumps for conveying and placing the ready-mixed concrete. There are pumps which lift the concrete to heights of up to 100 m. As their capacity is by far greater than that of cranes of hoists, they are used in particular for the construction of high piers, towers and silos with the aid of climbing formwork. Concrete pumps are generally mounted on lorries, and the rotary-drum lorries used for transporting ready-mixed concrete are now frequently equipped to deliver the concrete directly to the concrete pump without passing through a silo.
Formwork has followed the technical development rendered possible by the availability of larger tower cranes with longer arms and increased capacities, and it is no longer necessary to prepare shuttering in situ.
Prefabricated formwork up to 25 m2 in size is used in particular for making the vertical structures of large residential and industrial buildings, such as facades and dividing walls. These structural-steel formwork elements, which are prefabricated in the site shop or by the industry, are lined with sheet-metal or wooden panels. They are handled by crane and removed after the concrete has set. Depending on the type of building method, prefabricated formwork panels are either lowered to the ground for cleaning or taken to the next wall section ready for pouring.
So-called formwork tables are used to make horizontal structures (i.e., floor slabs for large buildings). These tables are composed of several structural-steel elements and can be assembled to form floors of different surfaces. The upper part of the table (i.e., the actual floor-slab form) is lowered by means of screw jacks or hydraulic jacks after the concrete has set. Special beak-like load-carrying devices have been devised to withdraw the tables, to lift them to the next floor and to insert them there.
Sliding or climbing formwork is used to build towers, silos, bridge piers and similar high structures. A single formwork element is prepared in situ for this purpose; its cross-section corresponds to that of the structure to be erected, and its height may vary between 2 and 4 m. The formwork surfaces in contact with the concrete are lined with steel sheets, and the entire element is linked to jacking devices. Vertical steel bars anchored in the concrete which is poured serve as jacking guides. The sliding form is jacked upwards as the concrete sets, and the reinforcement work and concrete placing continue without interruption. This means that work has to go on around the clock.
Climbing forms differ from sliding ones in that they are anchored in the concrete by means of screw sleeves. As soon as the poured concrete has set to the required strength, the anchor screws are undone, the form is lifted to the height of the next section to be poured, anchored and prepared for receiving the concrete.
So-called form cars are frequently used in civil engineering, in particular for making bridge deck slabs. Especially when long bridges or viaducts are built, a form car replaces the rather complex falsework. The deck forms corresponding to one length of bay are fitted to a structural-steel frame so that the various form elements can be jacked into position and be removed laterally or lowered after the concrete has set. When the bay is finished, the supporting frame is advanced by one bay length, the form elements are again jacked into position, and the next bay is poured
When a bridge is built using the so-called cantilever technique the form-supporting frame is much shorter than the one described above. It does not rest on the next pier but must be anchored to form a cantilever. This technique, which is generally used for very high bridges, often relies on two such frames which are advanced by stages from piers on both sides of the span.
Prestressed concrete is used particularly for bridges, but also in building especially designed structures. Strands of steel wire wrapped in steel-sheet or plastic sheathing are embedded in the concrete at the same time as the reinforcement. The ends of the strands or tendons are provided with head plates so that the prestressed concrete elements may be pretensioned with the aid of hydraulic jacks before the elements are loaded.
Construction techniques for large residential buildings, bridges and tunnels have been rationalized even further by prefabricating elements such as floor slabs, walls, bridge beams and so on, in a special concrete factory or near the construction site. The prefabricated elements, which are assembled on the site, do away with the erection, displacement and dismantling of complex formwork and falsework, and a great deal of dangerous work at height can be avoided.
Reinforcement is generally delivered to the site cut and bent according to bar and bending schedules. Only when prefabricating concrete elements on the site or in the factory are the reinforcement bars tied or welded to each other to form cages or mats which are inserted into the forms before the concrete is poured.
Prevention of accidents
Mechanization and rationalization have eliminated many traditional hazards on building sites, but have also created new dangers. For instance, fatalities due to falls from height have considerably diminished thanks to the use of form cars, form-supporting frames in bridge building and other techniques. This is due to the fact that the work platforms and walkways with their guard rails are assembled only once and displaced at the same time as the form car, whereas with traditional formwork the guard rails were often neglected. On the other hand, mechanical hazards are increasing and electrical hazards are particularly serious in wet environments. Health hazards arise from cement itself, from substances added for curing or waterproofing and from lubricants for formwork.
Some important accident prevention measures to be taken for various operations are given below.
As concrete is nearly always mixed by machine, special attention should be paid to the design and layout of switchgear and feed-hopper skips. In particular, when concrete mixers are being cleaned, a switch may be unintentionally actuated, starting the drum or the skip and causing injury to the worker. Therefore, switches should be protected and also arranged in such a manner that no confusion is possible. If necessary, they should be interlocked or provided with a lock. The skips should be free from danger zones for the mixer attendant and workers moving on passageways near it. It must also be ensured that workers cleaning the pits beneath feed-hopper skips are not injured by the accidental lowering of the hopper.
Silos for aggregates, especially sand, present a hazard of fatal accidents. For example, workers entering a silo without a standby person and without a safety harness and lifeline may fall and be buried in the loose material. Silos should therefore be equipped with vibrators and platforms from which sticking sand can be poked down, and corresponding warning notices should be displayed. No person should be allowed to enter the silo without another standing by.
Concrete handling and placing
The proper layout of concrete transfer points and their equipment with mirrors and bucket receiving cages obviates the danger of injuring a standby worker who otherwise has to reach out for the crane bucket and guide it to a proper position.
Transfer silos which are jacked up hydraulically must be secured so that they are not suddenly lowered if a pipeline breaks.
Work platforms fitted with guard rails must be provided when placing the concrete in the forms with the aid of buckets suspended from the crane hook or with a concrete pump. The crane operators must be trained for this type of work and must have normal vision. If large distances are covered, two-way telephone communication or walkie-talkies have to be used.
When concrete pumps with pipelines and placer masts are used, special attention should be paid to the stability of the installation. Agitating lorries (cement mixers) with built-in concrete pumps must be equipped with interlocked switches which make it impossible to start the two operations simultaneously. The agitators must be guarded so that the operating personnel cannot come into contact with moving parts. The baskets for collecting the rubber ball which is pressed through the pipeline to clean it after the concrete has been poured, are now replaced by two elbows arranged in opposite directions. These elbows absorb almost all the pressure needed to push the ball through the placing line; they not only eliminate the whip effect at the line end, but also prevent the ball from being shot out of the line end.
When agitating lorries are used in combination with placing plant and lifting equipment, special attention has to be paid to overhead electric lines. Unless the overhead line can be displaced they must be insulated or guarded by protective scaffolds within the work range to exclude any accidental contact. It is important to contact the power supply station.
Falls are common during the assembly of traditional formwork composed of square timber and boards because the necessary guard rails and toe boards are often neglected for work platforms which are only required for short periods. Nowadays, steel supporting structures are widely used to speed up formwork assembly, but here again the available guard rails and toe boards are frequently not installed on the pretext that they are needed for so short a time.
Plywood form panels, which are increasingly used, offer the advantage of being easy and quick to assemble. However, often after being used several times, they are frequently misappropriated as platforms for rapidly required scaffolds, and it is generally forgotten that the distances between the supporting transoms must be considerably reduced in comparison with normal scaffold planks. Accidents resulting from breakage of form panels misused as scaffold platforms are still rather frequent.
Two outstanding hazards must be borne in mind when using prefabricated form elements. These elements must be stored in such a manner that they cannot turn over. Since it is not always feasible to store form elements horizontally, they must be secured by stays. Form elements permanently equipped with platforms, guard rails and toeboards may be attached by slings to the crane hook as well as being assembled and dismantled on the structure under construction. They constitute a safe workplace for the personnel and do away with the provision of work platforms for placing the concrete. Fixed ladders may be added for safer access to platforms. Scaffold and work platforms with guard rails and toe boards permanently attached to the form element should be used in particular with sliding and climbing formwork.
Experience has shown that accidents due to falls are rare when work platforms do not have to be improvised and rapidly assembled. Unfortunately, form elements fitted with guard rails cannot be used everywhere, especially where small residential buildings are being erected.
When the form elements are raised by crane from storage to the structure, lifting tackle of appropriate size and strength, such as slings and spreaders, must be used. If the angle between the sling legs is too large, the form elements must be handled with the aid of spreaders.
The workers cleaning the forms are exposed to a health hazard which is generally overlooked: the use of portable grinders to remove concrete residues adhering to the form surfaces. Dust measurements have shown that the grinding dust contains a high percentage of respirable fractions and silica. Therefore, dust control measures must be taken (e.g., portable grinders with exhaust devices linked to a filter unit or an enclosed form-board cleaning plant with exhaust ventilation.
Assembly of prefabricated elements
Special lifting equipment should be used in the manufacturing plant so that the elements can be moved and handled safely and without injury to the workers. Anchor bolts embedded in the concrete facilitate their handling not only in the factory but also on the assembly site. To avoid bending of the anchor bolts by oblique loads, large elements must be lifted with the aid of spreaders with short rope slings. If a load is applied to the bolts at an oblique angle, concrete may spill off and the bolts may be torn out. The use of inappropriate lifting tackle has caused serious accidents resulting from falling concrete elements.
Appropriate vehicles must be used for the road transport of prefabricated elements. They must be approximately secured against overturning or sliding—for example, when the driver has to brake the vehicle suddenly. Visibly displayed weight indications on the elements facilitate the task of the crane operator during loading, unloading and assembly on the site.
Lifting equipment on the site should be adequately chosen and operated. Tracks and roads must be kept in good condition in order to avoid overturning of loaded equipment during operation.
Work platforms protecting personnel against falls from height must be provided for the assembly of the elements. All possible means of collective protection, such as scaffolds, safety nets and overhead travelling cranes erected before completion of the building, should be taken into consideration before recourse is taken to reliance on PPE. It is, of course, possible to equip the workers with safety harnesses and lifelines, but experience has shown that there are workers who use this equipment only when they are under constant close supervision. Lifelines are indeed a hindrance when certain tasks are performed, and certain workers are proud of being capable of working at great heights without using any protection.
Before starting to design a prefabricated building, the architect, the manufacturer of the prefabricated elements and the building contractor should meet to discuss and study the course and safety of all operations. When it is known beforehand what types of handling and lifting equipment are available on the site, the concrete elements may be provided in the factory with fastening devices for guard rails and toe boards. The façade ends of floor elements, for instance, are then easily fitted with prefabricated guard rails and toe boards before the elements are lifted into place. The wall elements corresponding to the floor slab may thereafter be safely assembled because the workers are protected by guard rails.
For the erection of certain high industrial structures, mobile work platforms are lifted into position by crane and hung from suspension bolts embedded in the structure itself. In such cases it may be safer to transport the workers to the platform by crane (which should have high safety characteristics and be run by a qualified operator) than to use improvised scaffolds or ladders.
When post-tensioning concrete elements, attention should be paid to the design of the post-tensioning recesses, which should enable the tensioning jacks to be applied, operated and removed without any hazard for the personnel. Suspension hooks for tensioning jacks or openings for passing the crane rope must be provided for post-tensioning work beneath bridge decks or in box-type elements. This type of work, too, requires the provision of work platforms with guard rails and toe boards. The platform floor should be sufficiently low to allow for ample work space and safe handling of the jack. No person should be permitted at the rear of the tensioning jack because serious accidents may result from the high energy released in the breakage of an anchoring element or a steel tendon. The workers should also avoid being in front of the anchor plates as long as the mortar pressed into the tendon sheaths has not set. As the mortar pump is connected with hydraulic pipes to the jack, no person should be permitted in the area between pump and jack during tensioning. Continuous communication among the operators and with supervisors is also very important.
Thorough training of plant operators in particular and all construction site personnel in general is becoming more and more important in view of increasing mechanization and the use of many types of machinery, plant and substances. Unskilled labourers or helpers should be employed in exceptional cases only, if the number of construction site accidents is to be reduced.