The transportation and warehousing industry is fraught with challenges to worker health and safety. Those involved in loading and unloading of cargo and in storing, stacking and retrieving materials are prone to musculoskeletal injuries, slips and falls due to uncertain, irregular or slippery work surfaces and being struck by falling objects. See figure 1. Those operating and maintaining vehicles and other machinery are not only vulnerable to such injuries but also to the toxic effects of fuels, lubricants and exhaust fumes. If ergonomic principles are not heeded in the design of seats, pedals and instrument panels, drivers of trains, planes and motor vehicles (those used in warehousing as well on roads) will not only be subject to musculoskeletal disorders and undue fatigue, but will also be prone to operating mishaps that can lead to accidents.
Figure 1. Lifting parcels above shoulder height is an ergonomic hazard.
All workers—and the general public as well—may be exposed to toxic substances in the event of leaks, spills and fires. Since much of the work is done out-of-doors, transportation and warehousing workers are also subject to extremes of weather such as heat, cold, rain, snow and ice, which can not only make the work more arduous but also more dangerous. Aviation crews must adjust to changes in barometric pressure. Noise is a perennial problem for those operating or working near noisy vehicles and machinery.
Perhaps the most pervasive hazard in this industry is work stress. It has many sources:
Adjusting to work hours. Many workers in this industry are burdened by the necessity of adjusting to changing shifts, while flight crews who travel long east-west or west-east distances must adjust to changes in circadian body rhythms; both of these factors may cause drowsiness and fatigue. The danger of functional impairment due to fatigue has led to laws and regulations stipulating the number of hours or shifts that may be worked without a rest period. These are generally applicable to aviation flight crews, railroad train crews and, in most countries, drivers of road buses and trucks. Many of the last group are independent contractors or work for small enterprises and are frequently forced by economic pressures to flout these regulations. There are always emergencies dictated by problems with traffic, weather or accidents which require exceeding the work hours limits. Led by the airlines, large transportation companies are now using computers to track employees’ work schedules to verify their compliance with the regulations and to minimize the amount of down time for both workers and equipment.
Timetables. Most passenger and a good part of freight transport is guided by timetables stipulating departure and arrival times. The necessity of keeping to schedules which often allow too little leeway is often a very potent stressor for the drivers and their crews.
Dealing with the public. Meeting the sometimes unreasonable and often forcefully expressed demands of the public can be a significant source of stress for those dealing with passengers at terminals and ticket offices and en route. Drivers of road transport must contend with other vehicles, traffic regulations and diligent highway traffic officers.
Accidents. Accidents, whether due to equipment failure, human error or environmental conditions, place the transportation industry at or near the top of listings of occupational fatalities in most countries. Even when a particular worker’s injuries may not be serious, post-traumatic stress disorder (PTSD) can lead to profound and prolonged disability, and in some instances it can prompt changing to another job.
Isolation. Many employees in the transportation industry work alone with little or no human contact (e.g., truck drivers, workers in control rooms and in railroad switch and signal towers). If problems arise, there may be difficulty and delays in getting help. And, if they are not kept busy, boredom may lead to a drop in attentiveness that can presage accidents. Working alone, especially for those driving taxis, limousines and delivery trucks, is an important risk factor for felonious assaults and other forms of violence.
Being away from home. Transportation workers are frequently required to be away from home for periods of days or weeks (in the maritime industry, for months). In addition to the stress of living out of a suitcase, strange food and strange sleeping accommodations, there is the reciprocal stress of separation from family and friends.
Most industrialized countries require transportation workers, especially drivers and operating crew members, to take periodic medical examinations to verify that their physical and mental capacities meet the requirements established by regulations. Visual and hearing acuity, colour vision, muscular strength and flexibility and freedom from causes of syncope are some of the factors tested for. Accommodations, however, make it possible for many individuals with chronic disorders or disabilities to work without danger to themselves or others. (In the United States, for example, employers are mandated by the federal Americans With Disabilities Act to provide such accommodations.)
Drugs and alcohol
Prescription and over-the-counter medications taken for a variety of disorders (e.g., hypertension, anxiety and other hyperkinetic conditions, allergies, diabetes, epilepsy, headaches and the common cold) may cause drowsiness and affect alertness, reaction time and coordination, especially when alcoholic beverages are also consumed. Abuse of alcohol and/or illegal drugs is found frequently enough among transportation workers to have led to voluntary or legislatively mandated drug testing programmes.
The health and safety of workers in the transportation and warehousing industry are critical considerations, not only for the workers themselves but also for the public being transported or involved as bystanders. Safeguarding health and safety, therefore, is the joint responsibility of the employers, the employees and their unions and governments on all levels.
The transport sector encompasses industries that are involved in the transportation of goods and passengers throughout the world. This sector is structurally complex and vitally important to economies locally, nationally and globally.
The transport sector is vitally important to the economic viability of nations. Transportation plays a key role in economically important factors such as employment, utilization of raw and manufactured goods, investment of private and public capital and generation of tax revenues.
In most industrialized countries, transport accounts for 2 to 12% of the paid employment (ILO 1992). In the United States alone, the Department of Transportation reported that in 1993, there were approximately 7.8 million employees in trucking-related firms (DOT 1995). The transport sector’s share in the gross domestic product (GDP) and total employment tends to decrease as the country’s income increases.
The transport sector is also a major consumer of raw materials and finished goods in most industrialized countries. For example, in the United States, the transport sector utilizes approximately 71% of all rubber produced, 66% of all petroleum refined, 24% of all zinc, 23% of all cement, 23% of all steel, 11% of all copper and 16% of all aluminium (Sampson, Farris and Shrock 1990).
Capital investment utilizing public and private funds to purchase trucks, ships, airplanes, terminals and other equipment and facilities easily exceeds hundreds of billions of dollars in industrialized countries.
The transport sector also plays a major role in generating revenues in the form of taxes. In industrialized countries, transport of passengers and freight is often heavily taxed (Sampson, Farris and Shrock 1990; Gentry, Semeijn and Vellenga 1995). Typically these taxes take the form of fuel taxes on gasoline and diesel fuels, and excise taxes on freight bills and passenger tickets, and easily exceed hundreds of billions of dollars annually.
Evolution of the Sector
In the early stages of the transport sector, geography greatly influenced what was the dominant mode of transportation. As advances were made in construction technology, it became possible to overcome many of the geographical barriers that limited the development of the transport sector. As a result, the modes of transport that have dominated the sector evolved in accordance with the technology available.
Initially, water travel over the oceans was the primary mode of transport of freight and passengers. As large rivers were navigated and canals were built, the volume of inland transport over the waterways increased significantly. In the late nineteenth century, transport over railways began to emerge as the dominant mode of transport. Rail transport, because of its ability to overcome natural barriers such as mountains and valleys through the use of tunnels and bridges, offered flexibility that waterways could not provide. Furthermore, unlike transport over waterways, transport over the rails was virtually unaffected by winter conditions.
Many national governments recognized the strategic and economic advantages of rail transport. Consequently, rail companies were awarded governmental financial assistance to facilitate the expansion of rail networks.
In the early twentieth century, the development of the combustion engine combined with the increased use of motor vehicles enabled road transport to become an increasingly popular mode of transport. As the highway and throughway systems were developed, road transport enabled door-to-door deliveries of goods. This flexibility far surpassed that of railways and waterways. Eventually, as advances were made in road construction and improvements were made to the internal combustion engine, in many parts of the world road transport became faster than rail transport. Consequently, road transport has become the most used mode of transport of goods and passengers.
The transport sector continued to evolve with the advent of airplanes. The use of airplanes as a means to transport freight and passengers began during the Second World War. Initially, airplanes were primarily used to transport mail and soldiers. However, as aircraft construction was perfected and an increasing number of persons learned to operate airplanes, air transport grew in popularity. Today, air transport is a very fast, reliable mode of transport. However, in terms of total tonnage, air transport handles only a very small percentage of freight.
Structure of the Sector
Information on the structure of rail systems in industrialized countries is generally reliable and comparable (ILO 1992). Similar information on road systems is somewhat less reliable. Information on the structure of waterways is reliable, having not changed substantially in the past few decades. However, similar information regarding developing countries is scarce and unreliable.
European countries developed economic and political blocs that have had a significant impact on the transport sector. In Europe, road transport dominates the movement of freight and passengers. Trucking, with a heavy emphasis on less-than-trailer-load freight, is conducted by small national and regional carriers. This industry is heavily regulated and highly fractured. Since the early 1970s, the total volume of freight transported by road has increased by 240%. Conversely, rail transport has declined by approximately 8% (Violland 1996). However, several European countries are working diligently to increase the efficiency of rail transport and are promoting intermodal transport.
In the United States, the primary mode of transport is over the roadways. The Department of Transportation, Office of Motor Carriers, reported in 1993 that there were over 335,000 firms operating medium and heavy trucks (DOT 1995). This included large companies that transport their own products, smaller private firms, and for-hire truckload and less-than-truckload common and contract carriers. The majority of these fleets (58%) operate six or fewer trucks. These companies operate a total of 1.7 million combination units, 4.4 million single-unit medium and heavy trucks and 3.8 million trailers. The road system in the United States increased by roughly 2% from 1980 to 1989 (ILO 1992).
The rail systems in the United States have declined, due primarily to the loss of Class 1 status of some rail lines, and due to the abandonment of less profitable lines. Canada has increased its rail system by some 40%, due mainly to a change in the classification system. The road system in Canada has decreased by 9% (ILO 1992).
In the industrialized nations of the Pacific Rim, there is great variability of the rail and road systems, due mainly to the different levels of industrialization of the respective countries. For example, rail and road networks in the Republic of Korea are similar to those in Europe, whereas in Malaysia, the rail and road networks are significantly smaller, but experiencing tremendous growth rates (over 53% for roads since 1980) (ILO 1992).
In Japan, the transport sector is heavily dominated by road transport, which accounts for 90.5% of the total Japanese freight transport tonnage. Approximately 8.2% of the tonnage is transported by water and 1.2% by rail (Magnier 1996).
Developing countries in Asia, Africa and Latin America typically suffer from inadequate transport systems. There is significant work underway to improve the systems, but a lack of hard currency, skilled workers and equipment inhibits the growth. Transport systems have grown significantly in Venezuela, Mexico and Brazil.
The Middle East in general has experienced growth in the transport sector, with countries such as Kuwait and Iran leading the way. It should be noted that due to the large size of the countries, sparse populations and arid climatic conditions, unique problems are encountered that limit the development of transport systems in this region.
Figure 1. World road network distribution 1988-89, kilometers.
The transportation sector contributes significantly to employment in most countries in both the private and public sectors. However, as per capita income increases, the impact of the sector on total employment decreases. The overall number of workers in the transport industries has declined steadily since the 1980s. This loss of workforce in the sector is due to several factors, especially technological advances that have automated many of the jobs related to the construction, maintenance and operation of transport systems. In addition, many countries have passed legislation which deregulated many transport-related industries; this has ultimately resulted in the loss of jobs.
Workers who are currently employed in transport-related industries must be highly skilled and competent. Due to the rapid advances in technology experienced in the transport sector, these workers and prospective workers must receive continual training and retraining.
Adapted from Soskolne 1997, with permission.
Hazardous wastes include, among other things, radioactive materials and chemicals. The movement of these substances from their source to other locations has been termed “toxic trade”. It was in the late 1980s that concern was raised about toxic trade, in particular with Africa (Vir 1989). This set the stage for the recently recognized issue of environmental justice, in some situations also known as environmental racism (Coughlin 1996).
Vir (1989) pointed out that as environmental safety laws became increasingly stringent in Europe and in the United States, and as the cost of disposal increased, “dumpers” or “waste merchants” began to turn their attention to poorer nations as potential and willing recipients of their waste products, providing a much needed source of revenue to these poorer countries. Some of these countries had been willing to take such waste at a fraction of the cost that developed nations would otherwise have had to pay for their disposal. To “nations that are drowning economically, this is an attractive deal” (Vir 1989).
Asante-Duah, Saccomanno and Shortreed (1992) show the exponential growth in the United States in the production of hazardous wastes since 1970, with the costs associated with treatment and disposal similarly increasing. They argue in favour of a controlled hazardous waste trade, one that is “regulated and informed”. They note that “countries generating small quantities of hazardous wastes should view the waste trade as an important economic option, as long as the waste recipients do not compromise their environmental sustainability”. Hazardous wastes will continue to be generated and there are countries for which an increase in some of these substances would not increase the risk to health of either present or future generations. It might therefore be economically efficient for such countries to accept waste.
There are others who argue that waste should be disposed of only at the source and not be transported at all (Puckett and Fogel 1994; Cray 1991; Southam News 1994). The latter argue from the position that science is incapable of providing any guarantees about the absence of risk.
One ethical principle that emerges from the foregoing argument is that of respect for autonomy (i.e., respect for persons), which also includes questions of national autonomy. The crucial question is one of the ability of a recipient country to adequately assess the level of risk associated with a shipment of hazardous waste. Assessment presupposes full disclosure of the contents of a shipment from the originating country and a level of local expertise to assess any potential impacts on the recipient country.
Because communities in developing countries are less likely to be informed about the potential risks associated with waste shipments, the NIMBY phenomenon (i.e., not in my backyard) so evident in the more affluent regions of the world is less likely to manifest in poorer regions. Furthermore, workers in developing regions of the world tend not to have the infrastructure related to worker protection, including information concerning the labelling of products with which they come into contact. Hence, workers in poorer nations involved in the management, storage and disposal of hazardous waste would lack the training to know how to protect themselves. Regardless of these ethical considerations, in the final analysis the economic benefits to be derived from accepting such waste shipments would need to be weighed against any potential harms that could arise in the short, medium and longer terms.
A second ethical principle emerging from the preceding argument is that of distributive justice, which involves question regarding who takes risks and who derives benefits. When there is an imbalance between those who take risks and those who derive benefits, the principle of distributive justice is not being honoured. It has often been financially poor labourers who have been exposed to hazards without any ability to enjoy the fruits of their efforts. This has occurred in the context of production of relatively expensive merchandise in the developing world for the benefit of first world markets. Another example related to the testing of new vaccines or drugs on people in developing countries who could never afford access to them in their own countries.
Towards Controlling the Transport of Hazardous Wastes
Because of the recognized need to better control the dumping of hazardous wastes, the Basel Convention was entered into by ministers of 33 countries in March 1989 (Asante-Duah, Saccomanno and Shortreed 1992). The Basel Convention addressed the transboundary movements of hazardous wastes and required the notification and consent of recipient countries before any waste shipments could take place.
Subsequently, the United Nations Environment Programme (UNEP) launched its Cleaner Production Programme, in close cooperation with governments and industry, to advocate low- and non-waste technologies (Rummel-Bulska 1993). In March 1994, a full ban was introduced on all transboundary movements of hazardous wastes from the 24 rich industrialized countries of the Organization for Economic Cooperation and Development (OECD) to other states that are not members of the OECD. The ban was immediate for wastes bound for final disposal and enters into force at the beginning of 1998 for all hazardous wastes that are said to be destined for recycling or recovery operations (Puckett and Fogel 1994). The countries most opposed to the introduction of a total ban were Australia, Canada, Japan and the United States. Despite this opposition from a handful of powerful industrial governments through the penultimate vote, the ban was finally agreed to by consensus (Puckett and Fogel 1994).
Greenpeace has stressed the primary prevention approach to solving the mounting waste crisis by addressing the root cause of the problem, namely minimizing waste generation through clean production technologies (Greenpeace 1994a). In making this point, Greenpeace identified major countries exporting hazardous wastes (Australia, Canada, Germany, the United Kingdom and the United States) and some countries importing them (Bangladesh, China (including Taiwan), India, Indonesia, Malaysia, Pakistan, the Philippines, the Republic of Korea, Sri Lanka and Thailand). In 1993, Canada, for example, had exported some 3.2 million kilograms of ash containing lead and zinc to India, the Republic of Korea and Taiwan, China, and 5.8 million kilograms of plastic waste to Hong Kong (Southam News 1994). Greenpeace (1993, 1994b) also addresses the extent of the problem in terms of specific substances and approaches to disposal.
Epidemiology is at the centre of human health risk assessment, which is invoked when concern is raised by a community about the consequences, if any, of exposure to hazardous and potentially toxic substances. The scientific method that epidemiology brings to the study of the environmental determinants of ill health can be fundamental to protecting unempowered communities, both from environmental hazards and from environmental degradation. Risk assessment conducted in advance of a shipment likely would fall into the legal trade arena; when conducted after a shipment has arrived, risk assessment would be undertaken to determine whether or not any health concerns were justified from what likely would have been an illegal shipment.
Among the concerns to the risk assessor would be hazard assessment, i.e., questions about what hazards, if any, exist and in what quantities and in what form they might be present. In addition, depending on the type of hazard, the risk assessor must make an exposure assessment to establish what possibilities there are for people to be exposed to the hazardous substance(s) through inhalation, skin absorption or ingestion (by contamination of the food chain or directly on foodstuffs).
In terms of trade, autonomy would require the informed consent of the parties in a voluntary and non-coercive milieu. However, it is hardly possible that non-coerciveness could ever pertain in such a circumstance by virtue of the financial need of an importing developing world country. The analogue here is the now accepted ethical guideline which does not permit the coercion of participants in research through payment for anything but direct costs (e.g., lost wages) for the time taken to participate in a study (CIOMS 1993). Other ethical issues involved here would include, on the one hand, truth in the presence of unknowns or in the presence of scientific uncertainty and, on the other hand, the principle of caveat emptor (buyer beware). The ethical principle of non-maleficence requires the doing of more good than harm. Here the short-term economic benefits of any trade agreement to accept toxic wastes must be weighed against the longer term damage to the environment, the public health and possibly also to future generations.
Finally, the principle of distributive justice requires recognition by the parties involved in a trade deal as to who would be deriving the benefits and who would be taking the risks in any trade deal. In the past, general practices for dumping waste and for locating hazardous waste sites in unempowered communities in the United States have led to the recognition of the concern now known as environmental justice or environmental racism (Coughlin 1996). In addition, questions of environmental sustainability and integrity have become central concerns in the public forum.
Acknowledgements: Dr. Margaret-Ann Armour, Department of Chemistry, University of Alberta, provided valuable references on the topic of toxic trade as well as materials from the November 1993 Pacific Basin “Conference on Hazardous Waste” at the University of Hawaii.
The Greenpeace office in Toronto, Ontario, Canada, was most helpful in providing copies of the Greenpeace references cited in this article.
Workers involved in municipal waste disposal and handling face occupational health and safety hazards which are as diverse as the materials they are handling. Workers’ primary complaints relate to odour and upper respiratory tract irritation usually related to dust. However, actual occupational health and safety concerns vary with the work process and the waste stream characteristics (mixed municipal solid waste (MSW), sanitary and biological waste, recycled wastes, agricultural and food wastes, ash, construction debris and industrial wastes). Biological agents such as bacteria, endotoxins and fungi may present hazards, particularly for immune system-compromised and hypersensitive workers. In addition to safety concerns, health impacts have involved predominantly respiratory health problems among workers, including symptoms of organic dust toxic syndrome (ODTS), irritation of the skin, eyes and upper airways and cases of more severe pulmonary diseases such as asthma, alveolitis and bronchitis.
The World Bank (Beede and Bloom 1995) estimates that 1.3 billion tonnes of MSW were generated in 1990 which represents an average of two-thirds of a kilogram per person per day. In the US alone, an estimated 343,000 workers were involved in MSW collection, transport and disposal according to 1991 US Census Bureau statistics. In industrialized countries waste streams are increasingly distinct and work processes are increasingly complex. Efforts to segregate and better define the compositions of waste streams are often critical for identifying occupational hazards and appropriate controls and for controlling environmental impacts. Most waste disposal workers continue to face unpredictable exposures and risks from mixed wastes in dispersed open dumps, often with open burning.
The economics of waste disposal, reuse and recycling, as well as public health concerns, are driving rapid changes in waste handling globally to maximize recovery of resources and reduce dispersion of refuse into the environment. Depending on local economic factors this results in the adoption of either increasingly labour-intensive or capital-intensive work processes. Labour-intensive practices draw an increasing number of workers into hazardous work environments and commonly involve informal sector scavengers who sort mixed refuse by hand and sell recyclable and reusable materials. Increased capitalization has not automatically led to improvements in working conditions as increased work within confined spaces (e.g., in drum composting operations or incinerators), and increased mechanical processing of wastes can result in increased exposure to both airborne contaminants and mechanical hazards, unless proper controls are implemented.
Waste Disposal Processes
A variety of waste disposal processes are used, and as waste collection, transportation and disposal costs increase to meet increasingly stringent environmental and community standards, an increasing diversity of processes can be cost-justified. These processes break down into four basic approaches which may be used in combination or in parallel for various waste streams. The four basic processes are dispersal (land or water dumping, evaporation), storage/isolation (sanitary and hazardous waste landfills), oxidation (incineration, composting) and reduction (hydrogenation, anaerobic digestion). These processes share some general occupational hazards associated with waste handling, but also involve work-process-specific occupational hazards.
General Occupational Hazards in Waste Handling
Regardless of the specific disposal process being utilized, simply processing MSW and other wastes involves common defined hazards (Colombi 1991; Desbaumes 1968; Malmros and Jonsson 1994; Malmros, Sigsgaard and Bach 1992; Maxey 1978; Mozzon, Brown and Smith 1987; Rahkonen, Ettala and Loikkanen 1987; Robazzi et al. 1994).
Unidentified, highly hazardous materials are often intermixed with normal waste. Pesticides, flammable solvents, paints, industrial chemicals, and biohazardous waste, may all be intermixed with household waste. This hazard can be handled primarily through segregation of the waste stream and in particular separation of industrial and household waste.
Odours and exposure to mixed volatile organic compounds (VOCs) can induce nausea but are typically well below American Conference of Governmental Industrial Hygenists (ACGIH) threshold limit values (TLVs), even within enclosed spaces (ACGIH 1989; Wilkins 1994). Control typically involves isolation of the process, as in sealed anaerobic digesters or drum composters, minimizing worker contact through daily soil cover or transfer station cleanup and controlling biological degradation processes, particularly minimizing anaerobic degradation by controlling moisture content and aeration.
Insect- and rodent-borne pathogens can be controlled through daily cover of waste with soil. Botros et al. (1989) reported that 19% of garbage workers in Cairo had antibodies to Rickettsia Typhi (from fleas) which causes human rickettsial disease.
Injection or blood contact with infectious waste, such as needles and blood soiled waste, is best controlled at the generator by segregation and sterilization of such waste prior to disposal and disposal in puncture resistant containers. Tetanus is also a real concern should skin damage occur. Up-to-date immunization is required.
Ingestion of Giardia sp. and other gastrointestinal pathogens can be controlled by minimizing handling, reducing hand-to-mouth contact (including tobacco use), supplying safe drinking water, providing toilet and clean up facilities for workers and maintaining appropriate temperature in composting operations in order to destroy pathogens prior to dry handling and bagging. Precautions are particularly appropriate for Giardia found in sewage sludge and disposable baby diapers in MSW, as well as for tape and round worms from poultry and slaughterhouse wastes.
Inhalation of airborne bacteria and fungi is of particular concern when mechanical processing increases (Lundholm and Rylander 1980) with compactors (Emery et al. 1992), macerators or shredders, aeration, bagging operations and when moisture content is allowed to drop. This results in increased respiratory disorders (Nersting et al. 1990), bronchial obstruction (Spinaci et al. 1981) and chronic bronchitis (Ducel et al. 1976). Although there are no formal guidelines, the Dutch Occupational Health Association (1989) recommended that total bacteria and fungal counts should be kept below 10,000 colony forming units per cubic metre (cfu/m3) and below 500 cfu/m3 for any single pathogenic organism (outdoor air levels are about 500 cfu/m3 for total bacteria, indoor air is typically less). These levels may be regularly exceeded in composting operations.
Biotoxins are formed by fungi and bacteria including endotoxins formed by gram-negative bacteria. Inhaling or ingesting an endotoxin, even after killing the bacteria which produced it, can cause fever and flu-like symptoms without infection. The Dutch Working Group on Research Methods in Biological Indoor Air Pollution recommends that airborne gram-negative bacteria be kept below 1000 cfu/m3 to avoid endotoxin effects. Bacteria and fungi can produce a variety of other potent toxins which may also present occupational hazards.
Heat exhaustion and heat stroke can be serious concerns particularly where safe drinking water is limited and where PPE is utilized in sites known to contain hazardous wastes. Simple PVC-Tyvek suits show a heat stress equivalent of adding 6 to 11°C (11 to 20°F) to the ambient wet bulb globe temperature (WBGT) index (Paull and Rosenthal 1987). When the WBGT exceeds 27.7°C (82°F) conditions are considered hazardous.
Skin damage or disease are common complaints in waste handling operations (Gellin and Zavon 1970). Direct skin damage from caustic ash and other irritating waste contaminants, combined with high exposures to pathogenic organisms, frequent skin lacerations and punctures and, typically, poor availability of washing facilities result in a high incidence of skin problems.
Wastes contain a variety of materials that can cause lacerations or punctures. These are of particular concern in labour intensive operations such as waste sorting for recycling or manual turning of MSW compost and where mechanical processes such as compacting, crushing or shredding can create projectiles. The most critical control measures are safety glasses and puncture and slash resistant footwear and gloves.
Vehicular-use hazards include both operator hazards such as rollover and engulfment hazards and collision hazards with workers on the ground. Any vehicle that works on unsound or irregular surfaces should be equipped with rollover cages that will support the vehicle and allow the operator to survive. Pedestrian and vehicular traffic should be separated to the extent possible into distinct traffic areas, particularly where visibility is limited such as during open burning, at night and in composting yards where dense ground fogs may develop in cold weather.
Reports of increased atopic bronchopulmonary reactions such as asthma (Sigsgaard, Bach and Malmros 1990) and skin reactions can occur in waste workers, particularly where organic dust exposure levels are high.
Dispersion includes dumping waste into bodies of water, evaporation into the air or dumping with no effort at containment. Ocean dumping of MSW and hazardous wastes is rapidly declining. However, an estimated 30 to 50% of MSW is not collected in the cities of developing countries (Cointreau-Levine 1994) and is commonly burned or dumped in canals and streets, where it presents a significant public health threat.
Evaporation, sometimes with active heating at low temperatures, is used as a cost-saving alternative to incinerators or kilns, especially for volatile liquid organic contaminants such as solvents or fuel which are mixed with non-combustible wastes such as soil. Workers may face confined-space entry hazards and explosive atmospheres, especially in maintenance operations. Such operations should incorporate appropriate air emissions controls.
Isolation involves a combination of remote locations and physical containment in increasingly secure landfills. Typical sanitary landfills involve excavation with earth moving equipment, dumping of waste, compaction and daily cover with soil or compost to reduce pest infestations, odours and dispersion. Clay or impervious plastic caps and/or liners may be installed to limit water infiltration and leachate into groundwater. Test wells may be used to evaluate off-site leachate migration and to allow monitoring of leachate within the landfill. Workers include heavy equipment operators, truck drivers, spotters who may be responsible for rejecting hazardous waste and directing vehicle traffic flows and informal sector scavengers who may sort the waste and remove recyclables.
In areas dependent on coal or wood for fuel, ash can constitute a significant portion of the waste. Quenching prior to dumping, or segregation into ash monofills, may be necessary to avoid fires. Ash can cause skin irritation and caustic burns. Fly ash presents a variety of health hazards including respiratory and mucosal irritation as well as acute respiratory distress (Shrivastava et al. 1994). Low density fly ash can also constitute an engulfment hazard and can be unstable under heavy equipment and in excavations.
In many nations waste disposal continues to consist of simple dumping with open burning, which may be combined with informal scavenging of reusable or recyclable components with value. These informal sector workers face serious safety and health hazards. It is estimated that in Manila, Philippines, 7,000 scavengers work at the MSW dump, 8,000 in Jakarta and 10,000 in Mexico City (Cointreau-Levine 1994). Because of the difficulties in controlling work practices in informal work, an important step in controlling these hazards is to move separation of recyclables and reusables into the formal waste collection process. This may be performed by the waste generators, including consumers or household workers, by collection/sorting workers (e.g., in Mexico City collection workers officially spend 10% of their time sorting waste for sale of recyclables, and in Bangkok 40% (Beede and Bloom 1995)) or in pre-disposal waste separation operations (e.g., magnetic separation of metallic waste).
Open burning exposes workers to a potentially toxic mix of degradation products as discussed below. Because open burning can be used by informal scavengers to assist in separating metal and glass from combustible waste, it may be necessary to recover materials with salvage value prior to dumping in order to eliminate such open burning.
As hazardous wastes are successfully segregated from the waste stream, risks of MSW workers are reduced while quantities handled by hazardous waste site workers increase. Highly secure hazardous waste treatment and disposal sites depend on detailed manifesting of waste composition, high levels of worker PPE, and extensive worker training to control hazards. Secure landfills have unique hazards including slip and fall hazards where excavations are lined with plastic or polymer gels to reduce migration of leachate, potentially serious dermatological problems, heat stress related to work for extended periods in impermeable suits and supplied air quality control. Heavy equipment operators, labourers and technicians depend largely on PPE to minimize their exposures.
Oxidation (incineration and composting)
Open burning, incineration and waste-derived fuel are the most obvious examples of oxidation. Where the moisture content is low enough and the combustible content is high enough, increasing effort is made to utilize the fuel value in MSW either through the generation of waste-derived fuel as compressed briquettes or by incorporating electrical cogeneration or steam plants into municipal waste incinerators. Such operations can involve high levels of dry dusts due to efforts to produce a fuel with consistent heat value. Residual ash must still be disposed of, usually in landfills.
MSW incinerators involve a variety of safety hazards (Knop 1975). Swedish MSW incinerator workers showed increased ischemic heart disease (Gustavsson 1989), while a study of US incinerator workers in Philadelphia, Pennsylvania, failed to show a correlation between health outcomes and exposure groups (Bresnitz et al. 1992). Somewhat elevated blood lead levels have been identified in incinerator workers, primarily related to exposures to electrostatic precipitator ash (Malkin et al. 1992).
Ash exposures (e.g., crystalline silica, radioisotopes, heavy metals) can be significant not only in incinerator operations, but also at landfills and lightweight concrete plants where ash is used as aggregate. Although crystalline silica and heavy metal content vary with the fuel, this may present serious silicosis risk. Schilling (1988) observed lung function and respiratory symptom effects in ash exposed workers, but no changes observable by x ray.
Thermal degradation on pyrolysis products resulting from incomplete oxidation of many waste products can pose significant health risks. These products can include hydrogen chloride, phosgene, dioxins and dibenzofurans from chlorinated wastes, such as polyvinyl chloride (PVC) plastics and solvents. Non-halogenated wastes also can produce hazardous degradation products, including polyaromatic hydrocarbons, acrolein, cyanide from wools and silk, isocyanates from polyurethane and organotin compounds from a variety of plastics. These complex mixtures of degradation products can vary tremendously with waste composition, feed rates, temperature and available oxygen during combustion. While these degradation products are a significant concern in open burning, exposures in MSW incinerator workers appear to be relatively low (Angerer et al. 1992).
In MSW and hazardous waste incinerators and rotary kilns, control of combustion parameters and the residence time for waste vapours and solids at high temperatures is critical in destruction of wastes while minimizing the generation of more hazardous degradation products. Workers are involved in incinerator operation, loading and waste transfer into the incinerator, waste delivery and unloading from trucks, equipment maintenance, housekeeping and ash and slag removal. While incinerator design can limit necessary manual labour and worker exposures, with less capital-intensive designs there may be significant worker exposures and a need for regular confined space entry (e.g., chipping for removal of slag from glass waste from incinerator grates).
In aerobic biological processes the temperature and speed of oxidation are lower than incineration, but it is nevertheless oxidation. Composting of agricultural and yard wastes, sewage sludge, MSW and food wastes is increasingly common in city-scale operations. Rapidly developing technologies for biological remediation of hazardous and industrial wastes often involve a sequence of aerobic and anaerobic digestion processes.
Composting usually occurs either in wind rows (long piles) or in large vessels which provide aeration and mixing. The objective of composting operations is to create a mix of waste with optimum ratios of carbon and nitrogen (30:1) and then maintain moisture at 40 to 60% by weight, greater than 5% oxygen and temperature levels 32 to 60oC so that aerobic bacteria and other organisms can grow (Cobb and Rosenfield 1991). Following separation of recyclables and hazardous wastes (which typically involves hand sorting), MSW is shredded to create more surface area for biological action. Shredding can produce high noise and dust levels and significant mechanical guarding concerns. Some operations use ganged hammer-mills to allow reduced front-end sorting.
In-vessel or drum composting operations are capital intensive but allow more effective odour and process control. Confined space entry is a significant hazard for maintenance workers as high levels of CO2 may be released causing oxygen deficiency. Lockout of equipment prior to maintenance is also critical as mechanisms include internal screw-drives and conveyors.
In less capital intensive wind row composting operations, waste is shredded and placed in long piles which are mechanically aerated through perforated pipes or simply by turning, either with front-end loaders or manually. Wind rows may be covered or roofed to facilitate maintenance of constant moisture content. Where specialized wind row turning equipment is used, chain mixing-flails rotate at high speed through the compost and should be well guarded from human contact. As these flails rotate through the wind row, they eject objects which can become dangerous projectiles. Operators must assure safe clearance distances around and behind the equipment.
Regular temperature measurements with probes allow monitoring the progress of composting and assure high enough temperatures to kill pathogens while allowing adequate survival of beneficial organisms. At moisture contents of 20 to 45% when the temperature exceeds 93oC there can also be a spontaneous combustion fire hazard (much like a silo fire). This is most likely to occur when piles exceed 4 m in height. Fires can be avoided by keeping pile heights below 3 m, and turning when the temperature exceeds 60°C. Facilities should provide water hydrants and adequate access between wind rows for control of fires.
Hazards in composting operations include vehicle and mechanical hazards resulting from tractors and trucks involved in turning wind-rows of waste to maintain aeration and moisture content. In cooler climates the elevated temperatures of compost can produce dense ground fogs in a work area occupied by heavy equipment operators and pedestrian workers. Compost workers report more nausea, headache and diarrhoea than their counterparts in a drinking water plant (Lundholm and Rylander 1980). Odour problems can occur as a result of poor control of the moisture and air required for the composting to progress. If anaerobic conditions are allowed to occur, hydrogen sulphide, amines and other odorous materials are generated. In addition to typical disposal worker concerns, composting involving actively growing organisms can raise MSW temperatures high enough to kill pathogens, but can also produce exposures to moulds and fungi and their spores and toxins, especially in compost bagging operations and where compost is allowed to dry. Several studies have evaluated airborne fungi, bacteria, endotoxins and other contaminants (Belin 1985; Clark, Rylander and Larsson 1983; Heida, Bartman and van der Zee 1975; Lacey et al. 1990; Millner et al. 1994; van der Werf 1996; Weber et al. 1993) in composting operations. There is some indication of increased respiratory disorders and hypersensitivity reactions in compost workers (Brown et al. 1995; Sigsgaard et al. 1994). Certainly bacterial and fungal respiratory infections (Kramer, Kurup and Fink 1989) are a concern for immune-suppressed workers such as those with AIDS and those receiving cancer chemotherapy.
Reduction (hydrogenation and anaerobic digestion)
Anaerobic digestion for sewage and agricultural waste involves closed tanks, often with rotating brush contacts if nutrients are dilute, which can pose serious confined space entry concerns for maintenance workers. Anaerobic digesters are also commonly used in many countries as methane generators which may be fuelled with agricultural, sanitary or food wastes. Methane collection from MSW landfills and burning or compression for use is now required in many countries when methane generation exceeds specified thresholds, but most landfills have inadequate moisture for anaerobic digestion to proceed efficiently. Hydrogen sulphide generation is also a common result of anaerobic digestion and can cause eye irritation and olfactory fatigue at low levels.
More recently, high temperature reduction/hydrogenation has become a treatment option for organic chemical wastes. This can involve smaller, and therefore potentially mobile, installations with less energy input than a high temperature incinerator because metallic catalysts allow hydrogenation to proceed at lower temperatures. Organic wastes can be converted into methane and used as fuel to continue the process. Critical worker safety concerns include explosive atmospheres and confined space entry for cleaning, sludge removal and maintenance, hazards of transporting and loading the liquid feed wastes and spill response.
As wastes are viewed as resources for recycling and reuse, waste processing increases, resulting in rapid change in the waste disposal industry globally. Occupational health and safety risks of waste disposal operations often go beyond obvious safety hazards to a variety of chronic and acute health concerns. These hazards are often faced with minimal PPE and inadequate sanitary and wash-up facilities. Industrial waste reduction and pollution prevention efforts are increasingly shifting recycling and reuse processes away from contracted or external waste disposal operations and into production work areas.
Top priorities in controlling occupational safety and health hazards in this rapidly changing industry sector should include:
In this period of rapid change in the industry, significant improvements in worker health and safety can be made at low cost.
Recycling means different things to different people. To consumers, recycling may mean putting out bottles and cans for curbside collection. To a product maker—a manufacturer of raw materials or fabricator of goods—it means including recycled materials in the process. To recycling service providers, recycling can mean providing cost-efficient collection, sorting and shipping services. For scavengers, it means culling recyclable materials from garbage and waste cans and selling them to recycling depots. To public policy makers in all levels of government, it means establishing regulations governing collection and utilization as well as reducing the volume of waste to be disposed of and deriving revenue from the sale of the recycled materials. For recycling to work effectively and safely, these diverse groups must be educated to work together and share responsibility for its success.
The recycling industry had been growing steadily since its inception a century ago. Until the 1970s, it remained basically unchanged as a voluntary private sector effort conducted largely by scrap dealers. With the advent of incineration in the 1970s, it became desirable to separate out certain materials before putting waste into the furnaces. This concept was introduced to address the emission problems created by metals, batteries, plastics and other materials discarded in urban wastes which were causing many old incinerators to be shut down as environmental polluters. The increasing concern about the environment provided the primary impetus for the organized separation of plastics, aluminium, tin, paper and cardboard from the residential waste stream. Initially, the recycling industry was not economically viable as a self-sustaining business, but by the mid 1980s, the need for the materials and the increase in their prices led to the development of many new material recycling facilities (MRFs) to handle commingled recyclable materials across the US and Europe.
The broad range of skills and expertise makes the range of employment for a MRF very wide. Whether it is a full-service MRF or a single sorting-line operation, the following groups of workers are generally employed:
Processes and Facilities
The recycling industry has been growing very rapidly and has evolved many different processes and procedures as the technology of sorting recyclable materials has advanced. The most common types of installation include full-service MRFs, non-waste stream MRFs and simple sorting and processing systems.
The full-service MRF receives recyclable materials mixed in the residential waste streams. Typically, the resident places the recyclables in coloured plastic bags which are then placed in the residential waste container. This allows the community to combine recyclable materials with other residential wastes, eliminating the need for separate collection vehicles and containers. A typical sequence of operations includes the following procedures:
Non-waste stream MRF
In this system, only the recyclables are delivered to the MRF; the residential wastes go elsewhere. It involves an advanced, semi-automated sorting and processing process system in which all of the steps are the same as those described above. Because of the smaller volume, fewer employees are involved.
Simple sorting/processing system
This is a labour-intensive system in which the sorting is performed manually. Typically, a conveyer belt is used to move material from one work station to another with each sorter removing one type of material as the belt passes his station. A typical sequence for such a simple, inexpensive processing system would include these processes:
Equipment and machinery
The machinery and equipment used in a MRF is determined by the type of process and the volumes of materials handled. In a typical semi-automated MRF, it would include:
Health and safety hazards
MRF workers face a large variety of environmental and work hazards, many of which are unpredictable since the content of the waste changes continually. Prominent among them are:
Table 1. Most frequent injuries in the recycling industry.
Cause of injury
Body part affected
Cuts, abrasions and lacerations
Contact with sharp materials
Hands and forearms
Particles in eye
Airborne dust and flying objects
MRF workers have the potential to be exposed to whatever wastes are delivered to it, as well as the ever-changing environment in which they work. The management of the facility must constantly be aware of the content of the material being delivered, the training and supervision of the workers and their compliance with safety rules and regulations, the proper use of PPE and the maintenance of machinery and equipment. The following safety considerations deserve constant close attention:
Municipal recycling is a relatively new industry that is changing rapidly as it grows and its technology advances. The health and safety of its workforce depend on proper design of processes and equipment and the proper training and supervision of its workers.
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
Prevention of dirt-borne disease, prevention of damage to vehicles by harmful objects and the joy of viewing a neat, attractive city are all benefits derived from clean streets. Herded animals or animal-drawn vehicles, which in earlier times caused unsanitary conditions, have generally ceased to be a problem; however, the expansion in world population with the resultant upsurge in waste generated, the increase in the number and size of factories, the growth in the number of vehicles and newspapers and the introduction of disposable containers and products have all contributed to the amount of street refuse and added to the street-cleaning problem.
Organization and Processes
Municipal authorities recognizing the threat to health posed by dirty streets have sought to minimise the danger by organizing street cleaning sections in the public works departments. In these sections, a superintendent responsible for scheduling frequency of cleaning various districts will have forepeople responsible for specific cleaning operations.
Normally, business districts will be swept daily while arterial roads and residential areas will be swept weekly. Frequency will depend upon rain or snowfall, topography and the education of the populace toward prevention of litter.
The superintendent will also decide the most effective means of achieving clean streets. These could be hand sweeping by one worker or a group, hose flushing or machine sweeping or flushing. Generally a combination of methods, depending on the availability of equipment, type of dirt encountered and other factors will be used. In areas of heavy snowfall, special snow-clearing equipment may be used on occasion.
Hand sweeping is generally done in the daytime and confined to cleaning of gutters or spot cleaning of pavements or adjacent areas. The equipment used consists of brooms, scrapers and shovels. One sweeper generally patrols a specified route and cleans about 9 km of curb per shift under favourable conditions; however, this may be reduced in congested business districts.
Dirt collected by one-person sweeping is placed in a cart which he or she pushes ahead and dumps in boxes placed at intervals along his or her route; these boxes are emptied periodically into refuse trucks. In group sweeping, dirt is swept into piles along the gutters and loaded directly into trucks. Normally a group of 8 sweepers will have 2 workers assigned as loaders. Group sweeping is particularly effective for massive clean-up jobs such as after storms, parades or other special events.
Advantages of hand sweeping are: it is easily adjusted to meet changing cleaning loads; it can be used in areas inaccessible to machines; it can be conducted in heavy traffic with minimum interference with vehicle movement; it can be done in freezing weather and it can be used on pavements where surface conditions do not permit machine cleaning. Disadvantages are: the work is dangerous in traffic; it raises dust; dirt piled in gutters may be dispersed by wind or traffic if not collected promptly; and hand sweeping may be costly in labour-expensive areas.
Hose flushing is not considered an economical operation today; however, it is effective where there is a large amount of dirt or mud adhering to the pavement surfaces, where there are large numbers of parked vehicles or in market areas. It is generally done at night by a two-person crew, one of whom handles the hose nozzle and directs the stream and the other connects hose to the hydrant. Equipment consists of hoses, hose nozzles and hydrant wrenches.
Machine sweepers consist of motorized chassis mounted with brushes, conveyors, sprinklers and storage bins. They are generally used in late evening or early morning hours in business districts and during the day in residential areas. Cleaning action is confined to the gutters and adjacent areas where most dirt accumulates.
The machine is operated by one worker and can be expected to clean approximately 36 km of curb during an 8 hour shift. Factors affecting output are: number of times and distance which must be travelled to dump dirt or pick up sprinkling water; traffic density; and amount of dirt collected.
The advantages of machine sweepers are: they clean well, rapidly and raise no dust when sprinklers are used; they pick up the dirt as they clean; they can be used at night; and they are relatively economical. The disadvantages are: they cannot clean under parked cars or in off-pavement areas; they are not effective on rough, wet or muddy streets; the sprinkler cannot be used in freezing weather and dry sweeping raises dust; and they require skilled operators and maintenance personnel.
Flushing machines are essentially water tanks mounted on a motorized chassis which is fitted with a pump and nozzle to provide pressure and direct the stream of water against the pavement surface. The machine can be expected to clean about 36 km of 7 m wide pavement during an 8 hour shift.
The advantages of flushing machines are: they can be used effectively on wet or muddy pavements; they clean rapidly, well and under parked cars without raising dust; and they can operate at night or in light traffic. The disadvantages are: they require additional cleaning to be effective where street, litter or sewer conditions are not favourable; they annoy pedestrians or vehicle operators who are splashed; they cannot be used in freezing weather; and they require skilled operators and maintenance personnel.
Hazards and Their Prevention
Street cleaning is a hazardous occupation due to the fact that it is conducted in traffic and is concerned with dirt and refuse, with the possibility of infection, cuts from broken glass, tins and so on. In crowded areas, hand sweepers may be exposed to a considerable amount of carbon monoxide and to a high level of noise.
Traffic hazards are protected against by training sweepers in ways of avoiding danger, such as arranging work against the traffic flow and providing them with highly visible clothing as well as attaching red flags or other warning devices to their carts. Machine sweepers and flushers are made visible by fitting them with flashing lights, waving flags and painting them distinctively.
Street cleaners, and in particular hand sweepers, are exposed to all the vagaries of weather and occasionally may have to work in very severe conditions. Illness, infection and handling accidents can in part be prevented by the use of PPE and in part by training. Mechanical equipment such as that used for snow cleaning should be operated only by trained workers.
There should be a conveniently accessible central point providing good washing facilities (including showers where practicable), a cloakroom with arrangements for changing and drying clothes, a messroom and a first-aid room. Periodical medical examination is desirable.
Environmental Concerns of Snow Disposal
Snow removal and disposal introduces a set of environmental concerns related to the potential deposition of debris, salts, oil, metals and particulates in local waterbodies. A particular danger exists from the concentration of particulates, such as lead, that originate in atmospheric emissions from industrialized areas and automobiles. The danger of melt-water runoff to aquatic organisms and the risk of soil and groundwater contamination has been countered by the adoption of safe handling practices that protect sensitive areas from exposure. Snow disposal guidelines have been adopted in several Canadian provinces (e.g., Quebec, Ontario, Manitoba).
Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety.
Waste water is treated in order to remove pollutants and to comply with the limits set by law. For this purpose an attempt is made to render the pollutants in the water insoluble in the form of solids (e.g., sludge), liquids (e.g., oil) or gases (e.g., nitrogen) by applying appropriate treatments. Well known techniques are then used to separate the treated waste water to be returned to the natural waterways from the pollutants rendered insoluble. The gases are dispersed into the atmosphere, while the liquid and solid residues (sludge, oil, grease) are usually digested before being submitted to further treatment. There may be single or multi-stage treatments according to the characteristics of the waste water and to the degree of purification required. Waste water treatment may be subdivided into physical (primary), biological (secondary) and tertiary processes.
The various physical treatment processes are designed to remove insoluble pollutants.
The sewage is made to pass through screens which retain coarse solids that may block or damage the treatment works equipment (e.g., valves and pumps). The screenings are processed according to local situations.
The sand contained in the waste water has to be removed as it tends to settle in the pipework on account of its high density and cause abrasion to the equipment (e.g., centrifugal separators and turbines). Sand is generally removed by passing the waste water through a channel of constant cross-section at a velocity of 15 to 30 cm/s. The sand collects on the channel bottom and may be used, after washing to remove putrescible matter, as an inert material, such as for road building.
Oils and non-emulsifiable fats have to be removed because they would adhere to the equipment of the treatment works (e.g., basins and clarifiers) and interfere with the subsequent biological treatment. Oil and fat particles are made to collect on the surface by passing the waste water at an appropriate velocity through tanks of rectangular cross-section; they are skimmed off mechanically and may be used as a fuel. Multi-plate separators of compact design and high efficiency are frequently used for oil removal: the sewage is made to pass from above through stacks of flat inclined plates; the oil adheres to the bottom surfaces of the plates and moves to the top where it is collected. With both these processes, the de-oiled water is discharged at the bottom.
Sedimentation, flotation and coagulation
These processes enable the solids to be removed from the waste water, heavy ones (greater than 0.4 μm in diameter) by sedimentation and light ones (less than 0.4 μm) by flotation. This treatment, too, relies on the differences in density of the solids and of the flowing waste water which is passed through sedimentation tanks and flotation tanks made of concrete or steel. The particles to be separated collect in the bottom or at the surface, settling or rising at velocities which are proportional to the square of the particle radius and to the difference between the particle density and the apparent waste water density. Colloidal particles (e.g., proteins, latexes and oily emulsions) with sizes from 0.4 to 0.001 μm are not separated, as these colloids become hydrated and usually negatively charged by adsorption of ions. Consequently the particles repel each other so that they cannot coagulate and separate. However, if these particles are “destabilized”, they coagulate to form flocks greater than 4 μm, which can be separated as sludge in conventional sedimentation or flotation tanks. Destabilization is obtained by coagulation, that is, by adding 30 to 60 mg/l of an inorganic coagulant (aluminium sulphate, iron (II) sulphate or iron (III) chloride). The coagulant hydrolyses under given pH (acidity) conditions and forms positive polyvalent metal ions, which neutralize the negative charge of the colloid. Flocculation (the agglomeration of coagulated particles in flocks) is facilitated by adding 1 to 3 mg/l of organic polyelectrolytes (flocculation agents), resulting in flocks of 0.3 to 1 μm diameter which are easier to separate. Sedimentation tanks of the horizontal-flow type may be used; they have rectangular cross-section and flat or sloping bottoms. The waste water enters along one of the head sides, and the clarified water leaves over the edge at the opposite side. Also vertical flow sedimentation tanks can be used which are cylindrical in shape and have a bottom like an inverted right circular cone; the waste water enters in the middle, and the clarified water leaves the tank over the top indented edge to be collected into an external circumferential channel. With the two types of tank, the sludge settles on the bottom and is conveyed (if necessary by means of a raking gear) into a collector. The solids concentration in the sludge is 2 to 10%, whereas that of the clarified water is 20 to 80 mg/l.
The flotation tanks are usually cylindrical in shape and have fine bubble air diffusers installed in their bottoms, the sewage entering the tanks in the centre. The particles adhere to the bubbles, float to the surface and are skimmed off, while the clarified water is discharged below. In the case of the more efficient “dissolved-air floating tanks”, the waste water is saturated with air under a pressure of 2 to 5 bars and then allowed to expand in the centre of the floating tank, where the minute bubbles resulting from the decompression make the particles float to the surface.
Compared to sedimentation, flotation yields a thicker sludge at a higher particle separation velocity, and the equipment required is therefore smaller. On the other hand, the operating cost and the concentration of solids in the clarified water are higher.
Several tanks arranged in series are required for coagulating and flocculating a colloidal system. An inorganic coagulant and, if necessary, an acid or an alkali to correct the pH value are added to the waste water in the first tank, which is equipped with an agitator. The suspension is then passed into a second tank equipped with a high-speed agitator; here, the polyelectrolyte is added and dissolved within a few minutes. The flock growth takes place in a third tank with a slow-running agitator and is carried out for 10 to 15 minutes.
Biological treatment processes remove organic biodegradable pollutants by use of micro-organisms. These organisms digest the pollutant by an aerobic or anaerobic process (with or without supply of atmospheric oxygen) and convert it into water, gases (carbon dioxide and methane) and a solid insoluble microbic mass which can be separated from the treated water. Especially in the case of industrial effluents proper conditions for the development of micro-organisms must be assured: presence of nitrogen and phosphorus compounds, traces of microelements, absence of toxic substances (heavy metals, etc.), optimum temperature and pH value. Biological treatment includes aerobic and anaerobic processes.
The aerobic processes are more or less complex according to the space available, the degree of purification required and the composition of the waste water.
These are generally rectangular and 3 to 4 m deep. The sewage enters at one end, is left for 10 to 60 days and leaves the pond partly at the opposite end, partly by evaporation and partly by infiltration into the ground. The purification efficiency ranges from 10 to 90% according to the type of effluent and to the residual 5-day biological oxygen demand (BOD5) content (<40 mg/l). Oxygen is supplied from the atmosphere by diffusion through the surface of the water and from photosynthetic algae. The solids in suspension in the waste water and those produced by microbial activity settle on the bottom, where they are stabilized by aerobic and/or anaerobic processes according to the depth of the ponds which affects the diffusion both of oxygen and sunlight. The oxygen diffusion is frequently accelerated by surface aerators, which enable the volume of the ponds to be reduced.
This type of treatment is very economical if space is available, but requires clay-like soil to prevent the pollution of underground water by toxic effluents.
This is used for an accelerated treatment carried out in concrete or steel tanks of 3 to 5 m depth where the waste water comes into contact with a suspension of micro-organisms (2 to 10 g/l) which is oxygenated by means of surface aerators or by blowing in air. After 3 to 24 hours, the mixture of treated water and micro-organisms is passed into a sedimentation tank where the sludge made up by micro-organisms is separated from the water. The micro-organisms are partly returned to the aerated tank and partly evacuated.
There are various types of activated-sludge processes (e.g., contact-stabilization systems and use of pure oxygen) which yield purification efficiencies of greater than 95% even for industrial effluents but they require accurate controls and high energy consumption for oxygen supply.
With this technique the micro-organisms are not kept in suspension in the waste water, but adhere to the surface of a filling material over which the sewage is sprayed. Air circulates through the material and supplies the required oxygen without any energy consumption. According to the type of waste water and to increase efficiency, part of the treated water is recirculated to the top of the filter bed.
Where land is available, low-cost filling materials of appropriate size (e.g., crushed stone, clinker and limestone) are used, and on account of the weight of the bed the percolating filter is generally constructed as a 1 m high concrete tank usually sunk in the ground. If there is not enough land, more costly lightweight packing materials such as high-rate plastic honeycomb media, with up to 250 square metres of surface area/cubic metre of media, are stacked in percolating towers up to 10 m high.
The waste water is distributed over the filter bed by a mobile or fixed sparging mechanism and collected in the floor to be eventually recirculated to the top and to be passed into a sedimentation tank where the sludge formed can settle. Openings at the bottom of the percolating filter allow for air circulation through the filter bed. Pollutants removal efficiencies of 30 to 90% are achieved. In many cases several filters are arranged in series. This technique, which requires little energy and is easy to operate, has found widespread use and is recommended for cases where land is available, for instance, in developing countries.
A set of flat plastic discs mounted parallel on a horizontal rotating shaft are partially immersed in the waste water contained in a tank. Due to the rotation the biological felt that covers the discs is brought into contact with the effluents and atmospheric oxygen. The biological sludge coming off the biodiscs remains in suspension in the waste water, and the system acts as activated sludge and sedimentation tank at the same time. Biodiscs are suitable for small to medium-sized industrial factories and communities, take up little space, are easy to operate, require little energy and yield efficiencies of up to 90%.
Anaerobic processes are carried out by two groups of micro-organisms—hydrolytic bacteria, which decompose complex substances (polysaccharides, proteins, lipids, etc.) to acetic acid, hydrogen, carbon dioxide and water; and methanogenic bacteria, which convert these substances to a biomass (that can be removed from the treated sewage by sedimentation) and to biogas containing 65 to 70% methane, the remainder being carbon dioxide, and having a high heat value.
These two groups of micro-organisms, which are very sensitive to toxic contaminants, act simultaneously in the absence of air at an almost neutral pH value, some requiring a temperature of 20 to 38oC (mesophilic bacteria) and other, more delicate ones, 60 to 65oC (thermophilic bacteria). The process is carried out in stirred, closed concrete or steel digesters, where the required temperature is held by thermostats. Typical is the contact process, where the digester is followed by a sedimentation tank to separate the sludge, which is partially recirculated to the digester, from the treated water.
Anaerobic processes need neither oxygen nor power for oxygen supply and yield biogas, which can be used as a fuel (low operating costs). On the other hand, they are less efficient than aerobic processes (residual BOD5: 100 to 1,500 mg/l), are slower and more difficult to control, but enable faecal and pathogenic micro-organisms to be destroyed. They are used for treating strong wastes, such as sedimentation sludge from sewage, sludge in excess from activated sludge or percolating-filter treatments and industrial effluents with a BOD5 up to 30,000 mg/l (e.g., from distilleries, breweries, sugar refineries, abattoirs and paper mills).
The more complex and more expensive tertiary processes make use of chemical reactions or specific chemicophysical or physical techniques to remove water-soluble non-biodegradable pollutants, both organic (e.g., dyes and phenols) and inorganic (e.g., copper, mercury, nickel, phosphates, fluorides, nitrates and cyanides), especially from industrial waste water, because they cannot be removed by other treatments. Tertiary treatment also enables a high degree of water purification to be obtained, and the water thus treated may be used as drinking water or for manufacturing processes (steam generation, cooling systems, process water for particular purposes). The most important tertiary processes are as follows.
Precipitation is carried out in reactors made of an appropriate material and equipped with agitators where chemical reagents are added at a controlled temperature and pH value to convert the pollutant to an insoluble product. The precipitate obtained in the form of sludge is separated by conventional techniques from the treated water. In waste water from the fertilizer industry, for instance, phosphates and fluorides are rendered insoluble by reaction with lime at ambient temperature and at an alkaline pH; chromium (tanning industry), nickel and copper (electroplating shops) are precipitated as hydroxides at an alkaline pH after having been reduced with m-disulphite at a pH of 3 or lower.
The organic pollutant is oxidized with reagents in reactors similar to those used for precipitation. The reaction is generally continued until water and carbon dioxide are obtained as final products. Cyanides, for instance, are destroyed at ambient temperature by adding sodium hypochlorite and calcium hypochlorite at alkaline pH, whereas azo- and anthraquinone-dyes are decomposed by hydrogen peroxide and ferrous sulphate at pH 4.5. Coloured effluents from the chemical industry containing 5 to 10% non-biodegradable organic substance are oxidized at 200 to 300°C at high pressure in reactors made of special materials by blowing air and oxygen into the liquid (wet oxidation); catalysts are sometimes used. Pathogens left in urban sewage after treatment are oxidized by chlorination or ozonisation to render the water drinkable.
Some pollutants (e.g., phenols in waste water from coking plants, dyes in water for industrial or drinking purposes and surfactants) are effectively removed by absorption on activated carbon powder or granules which are highly porous and have a large specific surface area (of 1000 m2/g or more). The activated carbon powder is added in metered quantities to the waste water in stirred tanks, and 30 to 60 minutes later the spent powder is removed as a sludge. Granulated activated carbon is used in towers arranged in series through which the polluted water is passed. The spent carbon is regenerated in these towers, that is, the absorbed pollutant is removed either by chemical treatment (e.g., phenols are washed out with soda) or by thermal oxidation (e.g., dyes).
Certain natural substances (e.g., zeolites) or artificial compounds (e.g., Permutit and resins) exchange, in a stoichiometric and reversible manner, the ions bound to them with those contained, even strongly diluted, in the waste water. Copper, chromium, nickel, nitrates and ammonia, for instance, are removed from waste water by percolation through columns packed with resins. When the resins are spent, they are reactivated by washing with regenerating solutions. Metals are thus recovered in a concentrated solution. This treatment, though costly, is efficient and advisable in cases where a high degree of purity is required (e.g., for waste water contaminated by toxic metals).
In special cases it is possible to extract water of high purity, suitable for drinking, from diluted waste water by passing it through semi-permeable membranes. On the waste water side of the membrane the pollutants (chlorides, sulphates, phosphates, dyes, certain metals) are left as concentrated solutions which have to be disposed of or treated for recovery. The diluted waste water is subjected to pressures up to 50 bars in special plant containing synthetic membranes made of cellulose acetate or other polymers. The operating cost of this process is low, and separation efficiencies of greater than 95% may be obtained.
Rendering pollutants insoluble during waste water treatment results in the production of considerable amounts of sludge (20 to 30% of the removed chemical oxygen demand (COD) which is strongly diluted (90 to 99% water)). The disposal of this sludge in a manner acceptable to the environment presupposes treatments with a cost of up to 50% of those required for waste water purification. The types of treatment depend on the destination of the sludge, depending in turn on its characteristics and on local situations. Sludge may be destined for:
The sludge is dewatered before its disposal to reduce both its volume and the cost of its treatment, and it is frequently stabilized to prevent its putrefaction and to render harmless any toxic substances it may contain.
Dewatering includes previous thickening in thickeners, similar to sedimentation tanks, where the sludge is left for 12 to 24 hours and loses part of the water which collects on the surface, while the thickened sludge is discharged below. The thickened sludge is dewatered, for example, by centrifugal separation or by filtration (under vacuum or pressure) with conventional equipment, or by exposure to the air in layers of 30 cm thick in sludge-drying beds consisting of rectangular concrete lagoons, approximately 50 cm deep, with a sloped bottom covered with a layer of sand to facilitate water drainage. Sludge containing colloidal substances should be previously destabilized by coagulation and flocculation, according to already described techniques.
Stabilization includes digestion and detoxification. Digestion is a long-term treatment of the sludge during which it loses 30 to 50% of its organic matter, accompanied by an increase in its mineral salt content. This sludge is no longer putrescible, any pathogens are destroyed and the filtrability is improved. Digestion may be of the aerobic type when the sludge is aerated during 8 to 15 days at ambient temperature in concrete tanks, the process being similar to activated-sludge treatment. It may be of the anaerobic type if the sludge is digested in plants similar to those used for the anaerobic waste treatment, at 35 to 40°C during 30 to 40 days, with the production of biogas. Digestion can be of the thermal type when the sludge is treated with hot air at 200 to 250°C and at a pressure of more than 100 bars during 15 to 30 minutes (wet combustion), or when it is treated, in the absence of air, at 180°C and at autogenous pressure, for 30 to 45 minutes.
Detoxification renders harmless sludge containing metals (e.g., chromium, nickel and lead), which are solidified by treatment with sodium silicate and autothermically converted into the corresponding insoluble silicates.
In many locations domestic waste collection is performed by municipal employees. In others, by private companies. This article provides an overview of processes and hazards that are based on observations and experiences in the Province of Quebec, Canada. Editor.
Besides the few workers employed by municipalities in the Province of Quebec, Canada, that have their own waste collection boards, thousands of waste collectors and drivers are employed in hundreds of companies in the private sector.
Many private enterprises rely, either wholly or partially, upon jobbers who rent or own trucks and are responsible for the collectors who work for them. Competition in the sector is high, as municipal contracts are awarded to the lowest bidder, and there is a regular annual turnover of enterprises. The high competition also results in low and stable domestic waste-collection rates, and waste collection accounts for the lowest proportion of municipal taxes. However, as the existing landfills fill up, landfill costs rise, obliging municipalities to consider integrated waste-management systems. All municipal workers are unionized. Unionization of private-sector workers began in the 1980s, and 20 to 30% of them are now unionized.
Waste collection is a dangerous trade. If we recognize that garbage trucks are similar to hydraulic presses, it follows that waste collection is like working on a mobile industrial press under conditions much more demanding than those encountered in most factories. In waste collection, the machine travels through traffic in all seasons and workers must feed it by running behind it and tossing irregular objects of variable volume and weight, containing invisible and hazardous objects, into it. On average, collectors handle 2.4 tonnes of waste per hour. The efficiency of waste collection operations is entirely dependent on determinants of work rate and rhythm. The need to avoid rush-hour traffic and bridge line-ups creates time pressures at collection points and during transport. Speed is again of importance during unloading at landfills and incinerators.
Several aspects of waste collection influence workload and hazards. First, remuneration is on a flat-rate basis, that is, the territory specified by contract must be completely cleared of domestic waste on collection day. Since the volume of waste depends on residents’ activities and varies from day to day and from season to season, the workload varies enormously. Secondly, workers are in direct contact with the objects and waste collected. This is quite different from the situation in the commercial and industrial waste-collection sectors, where waste-filled containers are collected by either front-loading trucks equipped with automated fork-lifts or by roll-off trucks. This means that workers in those sectors do not handle the waste containers and are not in direct contact with the waste. Working conditions for these collectors therefore more closely resemble those of domestic waste drivers, rather than domestic waste collectors.
Residential collection (also known as domestic collection) is, on the other hand, primarily manual, and workers continue to handle a wide variety of objects and containers of variable size, nature and weight. A few suburban and rural municipalities have implemented semi-automated collection, involving the use of mobile domestic waste bins and side-loading collectors (figure 1). However, most domestic waste continues to be collected manually, especially in cities. The principal characteristic of this job is thus significant physical exertion.
Figure 1. Automatic, side-loading refuse collector.
Pak Mor Manufacturing Company
A study involving field observations and measurements, interviews with management and workers, statistical analysis of 755 occupational accidents and analysis of video sequences revealed a number of potential hazards (Bourdouxhe, Cloutier and Guertin 1992).
On average, waste collectors handle 16,000 kg spread out over 500 collection points every day, equivalent to a collection density of 550 kg/km. Collection takes almost 6 hours, equivalent to 2.4 tonnes/hour, and involves walking 11 km during a total work day of 9 hours. Collection speed averages 4.6 km/h, over a territory of almost 30 km of sidewalks, streets and lanes. Rest periods are limited to a few minutes precariously balanced on the rear platform, or, in the case of driver-collectors of side-loading trucks, at the wheel. This demanding workload is exacerbated by such factors as the frequency of truck dismounts and mounts, the distance covered, travel modes, the static effort required to maintain one’s balance on the rear platform (a minimum of 13 kg of force), the frequency of handling operations per unit time, the variety of postures required (bending movements), the frequency of tosses and twisting movements of the trunk and the high collection rate per unit time in some sectors. The fact that the Association française de normalisation (AFNOR) adapted weight standard for manual handling was exceeded in 23% of observed trips is eloquent testimony of the impact of these factors. When workers’ capacities (established to be 3.0 tonnes/hour for rear-loading trucks, and 1.9 tonnes/hour for side-loading ones) are taken into account, the frequency with which the AFNOR standard is exceeded rises to 37%.
Diversity and nature of objects handled
Manipulation of objects and containers of variable weight and volume interrupts the smooth flow of operations and breaks work rhythms. Objects in this category, often hidden by residents, include heavy, large or bulky objects, sharp or pointed objects and hazardous materials. The most frequently encountered hazards are listed in table 1.
Table 1. Hazardous objects found in domestic waste collections.
Glass, window panes, fluorescent tubing
Battery acid, cans of solvent or paint, aerosol containers, gas cylinders, motor oil
Construction waste, dust, plaster, sawdust, hearth cinders
Pieces of wood with nails in them
Syringes, medical waste
Garden waste, grass, rocks, earth
Furniture, electrical appliances, other large domestic trash
Pre-compacted waste (in apartment buildings)
Excessive numbers of small containers from small businesses and restaurants
Large amounts of vegetable and animal waste in rural sectors
Prohibited containers (e.g., no handles, excessive weight, 55-gallon oil drums, thin-necked drums, garbage cans without covers)
Small, apparently light bags that are in fact heavy
Excessive numbers of small bags
Paper bags and boxes that rip
All waste that is hidden because of its excessive weight or toxicity, or that surprises unprepared workers
Commercial containers that must be emptied with an improvised system, which is often inappropriate and dangerous
Workers are greatly helped by having residents sort waste into colour-coded bags and mobile domestic bins which facilitate the collection and allow better control of work rhythm and effort.
Climatic conditions and the nature of objects transported
Wet paper bags and poor-quality plastic bags that rip and scatter their contents over the sidewalk, frozen garbage cans and domestic bins stuck in snow banks can cause mishaps and dangerous recovery manoeuvres.
The need to rush, traffic problems, parked cars and crowded streets all can contribute to dangerous situations.
In an attempt to reduce their workload and maintain a high but constant work rhythm in the face of these constraints, workers often attempt to save time or effort by adopting work strategies that may be hazardous. The most commonly observed strategies included kicking bags or cardboard boxes towards the truck, zigzagging across the road to collect from both sides of the street, grabbing bags while the truck is in motion, carrying bags under the arm or against the body, using the thigh to help load bags and garbage cans, hand-picking of waste scattered on the ground and manual compaction (pushing garbage overflowing the hopper with the hands when the compacting system is incapable of processing the load rapidly enough). For example, in suburban collection with a rear-loading truck, almost 1,500 situations were observed per hour that could result in accidents or increase workload. These included:
Collection with side-loading trucks (see figure 1) or small mobile domestic bins reduces the manipulation of heavy or dangerous objects and the frequency of situations that could result in accidents or an increase in workload.
Use of public thoroughfares
The street is the collectors’ workplace. This exposes them to such hazards as vehicular traffic, blocked access to residents’ waste receptacles, accumulation of water, snow, ice and neighbourhood dogs.
Rear-loading trucks (figure 2) often have excessively high or shallow steps and rear platforms that are difficult to mount and render descents perilously similar to jumps. Hand-rails that are too high or too close to the truck body only worsen the situation. These conditions increase the frequency of falls and of collisions with structures adjacent to the rear platform. In addition, the upper edge of the hopper is very high, and shorter workers must expend additional energy lifting objects into it from the ground. In some cases, workers use their legs or thighs for support or additional power when loading the hopper.
Figure 2. Back-loading enclosed compactor truck.
National Safety Council (US) The packer-blade comes down within centimetres of the edge of the platform. The blade has the capacity to cut protruding objects.
The characteristics of side-loading trucks and the operations related to their loading result in specific repetitive movements likely to cause muscle and joint problems in the shoulder and upper back. Driver-collectors of side-loading trucks have an additional constraint, as they must cope with both the physical strain of collection and the mental strain of driving.
Personal protective equipment
While the theoretical value of PPE is beyond question, it may nevertheless prove inadequate in practice. In concrete terms, the equipment may be inappropriate for the conditions under which collection is carried out. Boots, in particular, are incompatible with the narrow utilizable height of rear platforms and the high work rhythm necessitated by the manner in which collection is organized. Strong, puncture-resistant yet flexible gloves are valuable in protecting against hand injuries.
Some aspects of work organization increase workload and, by extension, hazards. In common with most flat-rate situations, the main advantage to workers of this system is the ability to manage their work time and save time by adopting a rapid work rhythm as they see fit. This explains why attempts, based on safety considerations, to slow down the pace of work have been unsuccessful. Some work schedules exceed workers’ capacities.
The role of the myriad variations of residents’ behaviour in the creation of additional hazards merits a study in itself. Prohibited or dangerous wastes skilfully hidden in regular waste, non-standard containers, excessively large or heavy objects, disagreements over collection times and non-conformity with bylaws all increase the number of hazards—and the potential for conflicts between residents and collectors. Collectors are often reduced to the role of “garbage police”, educators and buffers between municipalities, enterprises and residents.
Collection of materials for recycling is not without its own problems despite a low waste density and collection rates far below those of traditional collection (with the exception of the collection of leaves for composting). The hourly frequency of situations that could result in accidents is often high. The fact that this is a new type of work for which few workers have been trained should be borne in mind.
In several cases, workers are obliged to perform such dangerous activities as mounting the truck’s compaction box to get into the compartments and move piles of paper and cardboard with their feet. Several work strategies aimed at speeding up work rhythm have also been observed, e.g., hand re-sorting of the material to be recycled and removing objects from the recycling box and carrying them to the truck, rather than carrying the box to the truck. The frequency of mishaps and disruptions of normal work activity in this type of collection is particularly high. These mishaps result from workers doing ad hoc activities that are themselves dangerous.
Occupational Accidents and Prevention
Domestic waste collection is a dangerous trade. Statistics support this impression. The average annual accident rate in this industry, for all types of enterprise, truck and trade, is almost 80 accidents for every 2,000 hours of collection. This is equivalent to 8 workers of every 10 suffering an injury at least once a year. Four accidents occur for every 1,000 10-tonne truckloads. On average, each accident results in 10 lost workdays and accident compensation of $820 (Canadian). Indices of injury frequency and severity vary among enterprises, with higher rates observed in municipal enterprises (74 accidents/100 workers versus 57/100 workers in private enterprises) (Bourdouxhe, Cloutier and Guertin 1992). The most common accidents are listed in table 2.
Table 2. Most common accidents in domestic waste collection, Quebec, Canada.
Per cent of accidents studied
Back or shoulder pain
Tossing or twisting movements during collection of bags
Excessive efforts while lifting objects
Falls or slips while dismounting from the truck or moving in its vicinity
Crushed hands, fingers, arms or knees
Struck by containers or heavy objects, being caught between the vehicle and containers, or collisions with part of the vehicle or parked cars
Hand and thigh lacerations of variable depth
Glass, nails, or syringes, occurring during hopper loading
Scrapes and bruises
Contact or collisions
Eye or respiratory-tract irritation
Dust or splashes of liquids occurring during work near the hopper during compaction
Collectors typically suffer hand and thigh lacerations, drivers typically suffer sprained ankles resulting from falls during cabin dismounts and driver-collectors of side-loading trucks typically suffer shoulder and upper back pain resulting from tossing movements. The nature of the accidents also depends on the type of truck, although this can also be seen as a reflection of the specific trades associated with rear- and side-loading trucks. These differences are related to equipment design, the type of movements required and the nature and density of waste collected in the sectors in which these two types of truck are used.
The following are ten categories in which improvements could make domestic waste collection safer:
Domestic waste collection is an important but hazardous activity. Protection of workers is made more difficult where this service is contracted out to private sector enterprises which, as in the province of Quebec, may subcontract the work to many smaller jobbers. A large number of ergonomic and accident hazards, compounded by work quotas, adverse weather and local street and traffic problems must be confronted and controlled if workers’ health and safety are to be maintained.
Without treatment of waste the current concentration of people and industry in many parts of the world would very quickly make portions of the environment incompatible with life. Although reduction of the amount of waste is important, the proper treatment of waste is essential. Two basic types of waste enter a treatment plant, human/animal waste and industrial waste. Humans excrete about 250 grams of solid waste per capita per day, including 2000 million coliform and 450 million streptococci bacteria per person per day (Mara 1974). Industrial solid waste production rates range from 0.12 tons per employee per year at professional and scientific institutions to 162.0 tons per employee per year at sawmills and planing mills (Salvato 1992). Although some waste treatment plants are exclusively dedicated to handling one or the other type of material, most plants handle both animal and industrial waste.
Hazards and Their Prevention
The goal of waste water treatment plants is to remove as much of the solid, liquid and gaseous contaminants as possible within technically feasible and financially achievable constraints. There are a variety of different processes that are used to remove contaminants from waste water including sedimentation, coagulation, flocculation, aeration, disinfection, filtration and sludge treatment. (See also the article “Sewage treatment” in this chapter.) The specific hazard associated with each process varies depending on the design of the treatment plant and the chemicals used in the different processes, but the types of hazard can be classified as physical, microbial and chemical. The key to preventing and/or minimizing the adverse effects associated with working in sewage treatment plants is to anticipate, recognize, evaluate and control the hazards.
Figure 1. Manhole with cover removed.
Mary O. Brophy
Physical hazards include confined spaces, inadvertent energizing of machines or machine parts and trips and falls. The result of an encounter with a physical hazards can often be immediate, irreversible and serious, even fatal. Physical hazards vary with the design of the plant. Most sewage treatment plants, however, have confined spaces which include underground or below grade vaults with limited access, manholes (figure 1) and the sedimentation tanks when they have been emptied of liquid content during, for example, repairs (figure 2). Mixing equipment, sludge rakes, pumps and mechanical devices used for a variety of operations in sewage treatment plants can maim, and even kill, if they are inadvertently activated when a worker is servicing them. Wet surfaces, often encountered in sewage treatment plants, contribute to slipping and falling hazards.
Figure 2. Empty tank in a sewage treatment plant.
Mary O. Brophy
Confined-space entry is one of the most common and one of the most serious hazards faced by sewage treatment workers. A universal definition of a confined space is elusive. In general, however, a confined space is an area with limited means of entry and egress that was not designed for continuous human habitation and that does not have adequate ventilation. Hazards occur when the confined space is associated with a deficiency of oxygen, the presence of a toxic chemical or an engulfing material, such as water. Decreased oxygen levels can be the result of a variety of conditions including the replacement of oxygen with another gas, such as methane or hydrogen sulphide, the consumption of oxygen by the decay of organic material contained in the waste water or the scavenging of oxygen molecules in the rusting process of some structure within the confined space. Because low levels of oxygen in confined spaces cannot be detected by unaided human observation it is extremely important to use an instrument that can determine the level of oxygen before entering any confined space.
The earth’s atmosphere consists of 21% oxygen at sea level. When the percentage of oxygen in breathing air falls below about 16.5% a person’s breathing becomes more rapid and more shallow, the heart rate increases and the person begins to lose coordination. Below about 11% the person experiences nausea, vomiting, inability to move and unconsciousness. Emotional instability and impaired judgement may occur at oxygen levels somewhere between these two points. When individuals enter an atmosphere with oxygen levels below 16.5% they may immediately become too disoriented to get themselves out and eventually succumb to unconsciousness. If the oxygen depletion is great enough individuals can become unconscious after one breath. Without rescue they can die within minutes. Even if rescued and resuscitated, permanent damage can occur (Wilkenfeld et al. 1992).
Lack of oxygen is not the only hazard in a confined space. Toxic gases can be present in a confined space at a concentration level high enough to do serious harm, even kill, despite adequate oxygen levels. The effects of toxic chemicals encountered in confined spaces are discussed further below. One of the most effective ways to control the hazards associated with low oxygen levels (below 19.5%) and atmospheres contaminated with toxic chemicals is to thoroughly and adequately ventilate the confined space with mechanical ventilation prior to allowing anyone to enter it. This is usually done with a flexible duct through which outside air is blown into the confined space (see figure 3). Care must be taken to ensure that fumes from a generator or the fan motor are not also blown into the confined space (Brophy 1991).
Figure 3. Air moving unit for entering a confined space.
Mary O. Brophy
Sewage treatment plants often have large pieces of machinery to move sludge or raw sewage from one place in the plant to another. When repairs are made on this type of equipment the entire machine should be de-energized. Furthermore, the switch to re-energize the equipment should be under the control of the person performing the repairs. This prevents another worker in the plant from inadvertently energizing the equipment. Development and implementation of procedures to achieve these goals is called a lockout/tagout programme. Mutilation of body parts, such as fingers, arms and legs, dismemberment and even death can result from ineffective or inadequate lockout/tagout programmes.
Sewage treatment plants often contain large tanks and storage containers. People sometimes need to work on top of the containers, or walk by pits that have been emptied of water and may contain an 8 to 10 foot (2.5 to 3 m) drop (see figure 4). Sufficient protection against falls as well as adequate safety training should be provided for the workers.
Microbial hazards are primarily associated with the treatment of human and animal waste. Although bacteria are often added to alter the solids contained in waste water, the hazard to sewage treatment workers comes primarily from exposure to micro-organisms contained in human and other animal waste. When aeration is used during the sewage treatment process these micro-organisms can become airborne. The long term effect on the immune system of individuals exposed to these micro-organisms for extended periods of time has not been conclusively evaluated. In addition, workers who remove solid refuse from the influent stream before any treatment is begun are often exposed to micro-organisms contained in material splashing onto their skin and making contact with the mucous membranes. The results of encountering micro-organisms found in sewage treatment plants for extended periods of time are often more subtle than resulting from acute intense exposures. Nevertheless, these effects can also be irreversible and serious.
The three main categories of microbes relevant to this discussion are fungi, bacteria and viruses. All three of these can cause acute illness as well as chronic disease. Acute symptoms including respiratory distress, abdominal pains and diarrhoea have been reported in waste treatment workers (Crook, Bardos and Lacey 1988; Lundholm and Rylander 1980). Chronic diseases, such as asthma and allergic alveolitis, have been traditionally associated with exposure to high levels of airborne microbes and, recently, with microbial exposure during the treatment of domestic waste (Rosas et al. 1996; Johanning, Olmstead and Yang 1995). Reports of significantly elevated concentrations of fungi and bacteria in waste treatment, sludge dewatering and composting facilities are beginning to be published (Rosas et al. 1996; Bisesi and Kudlinski 1996; Johanning Olmstead and Yang 1995). Another source of airborne microbes is the aeration tanks which are used in many sewage treatment plants.
In addition to inhalation, microbes can be transmitted through ingestion and through contact with skin that is not intact. Personal hygiene, including washing hands before eating, smoking and going to the bathroom, is important. Food, drink, eating utensils, cigarettes and anything that would be put into the mouth should be kept away from areas of possible microbial contamination.
Chemical encounters at waste treatment plants can be both immediate and fatal, as well as protracted. A variety of chemicals are used in the process of coagulation, flocculation, disinfection and sludge treatment. The chemical of choice is determined by the contaminant or contaminants in the raw sewage; some industrial waste requires somewhat exotic chemical treatment. In general, however, the primary hazards from chemicals used in the coagulation and flocculation processes are skin irritation and eye injury due to direct contact. This is especially true of solutions which have a pH (acidity) less than 3 or greater than 9. The disinfection of effluent is often achieved by using either liquid or gaseous chlorine. Use of liquid chlorine can cause eye injury if splashed into the eyes. Ozone and ultraviolet light are also used to achieve disinfection of the effluent.
One way to monitor the effectiveness of sewage treatment is to measure the amount of organic material which remains in the effluent after treatment is complete. This can be done by determining the amount of oxygen that would be required to biodegrade the organic material contained in 1 litre of liquid over a period of 5 days. This is referred to as the 5-day biological oxygen demand (BOD5).
Chemical hazards in sewage treatment plants arise from the decomposition of organic material which results in the production of hydrogen sulphide and methane, from toxic waste dumped down the sewer lines and from the contaminants produced by operations performed by the workers themselves.
Hydrogen sulphide is almost always found in waste treatment plants. Hydrogen sulphide, also known as sewer gas, has a distinctive, unpleasant smell, often identified as rotten eggs. The human nose, however, quickly becomes accustomed to the smell. People who are exposed to hydrogen sulphide often lose their ability to detect its odour (i.e., olfactory fatigue). Furthermore, even if the olfactory system is able to detect hydrogen sulphide, it is not able to accurately judge its concentration in the atmosphere. Hydrogen sulphide biochemically interferes with the electron transport mechanism and blocks the utilization of oxygen at the molecular level. The result is asphyxiation and ultimately death due to the lack of oxygen in the brainstem cells that control the breathing rate. High levels of hydrogen sulphide (greater than 100 ppm) can, and often do, occur in the confined spaces found in sewage treatment plants. Exposure to very high levels of hydrogen sulphide can result in almost instantaneous suppression of the respiratory centre in the brainstem. The US National Institute for Occupational Safety and Health (NIOSH) has identified 100 ppm of hydrogen sulphide as immediately dangerous to life and health (IDLH). Lower levels of hydrogen sulphide (less than 10 ppm) are almost always present in some areas of sewage treatment plants. At these lower levels hydrogen sulphide can be irritating to the respiratory system, be associated with headaches and result in conjunctivitis (Smith 1986). Hydrogen sulphide is produced whenever organic matter decays and, industrially, during the production of paper (Kraft process), the tanning of leather (hair removal with sodium sulphide), and the production of heavy water for nuclear reactors.
Methane is another gas produced by the decomposition of organic matter. In addition to displacing oxygen, methane is explosive. Levels can be reached which result in an explosion when a spark or source of ignition is introduced.
Plants that handle industrial waste should have a thorough knowledge of the chemicals used in each of the industrial plants that utilize their services and a working relationship with the management of those plants so that they are promptly informed of any changes in processes and waste contents. Dumping of solvents, fuels and any other substance into sewer systems presents a hazard to treatment workers not only because of the toxicity of the material dumped but also because the dumping is unanticipated.
Whenever any industrial operation, such as welding or spray painting, is performed in a confined space special care must be taken to provide sufficient ventilation to prevent an explosion hazard as well as to remove toxic material produced by the operation. When an operation performed in a confined space produces a toxic atmosphere it is often necessary to equip the worker with a respirator because ventilation of the confined space may not ensure that the concentration of the toxic chemical can be maintained below the permissible exposure limit. Selection and fitting of a proper respirator falls within the purview of industrial hygiene practice.
Another serious chemical hazard in sewage treatment plants is the use of gaseous chlorine to decontaminate the effluent from the plant. The gaseous chlorine comes in a variety of containers weighing from 70 kg to roughly 1 tonne. Some of the very large sewage treatment plants use chlorine delivered in railroad cars. Gaseous chlorine is extremely irritating to the alveolar portion of the lungs, even in levels as low as a few ppm. Inhalation of higher concentrations of chlorine can cause inflammation of the alveoli of the lung and produce the adult respiratory distress syndrome, which has a 50% death rate. When a sewage treatment plant utilizes large amounts of chlorine (1 tonne and greater) the hazard exists not only for the plant workers but for the surrounding community as well. Unfortunately, the plants that use the largest amounts of chlorine are often located in large metropolitan centres with high density of people. Other methods of decontamination of sewage treatment plant effluent are available, including ozone treatment, the use of liquid hypochlorite solution and ultraviolet irradiation.
Telecommunications is the act of communicating with others through the use of electronic equipment like telephones, computer modems, satellites and fibre optic cables. Telecommunications systems comprise telecommunications cables from the user to the local switching office (local loops), the switching facilities which provide the communications connection to the user, the trunks or channels that transmit calls between the switching offices and, of course, the user.
During the early to mid-twentieth century, telephone exchanges, electromechanical switching systems, cables, repeaters, carrier systems and microwave equipment were introduced. After this occurrence, telecommunications systems spread to the industrialized areas of the world.
From the 1950s to 1984, technological advances continued to appear. For example, satellite systems, improved cable systems, the use of digital technology, fibre optics, computerization and video telephony were introduced throughout the communications industry. These changes allowed for the expansion of telecommunications systems throughout more areas of the world.
In 1984 a court ruling in the United States led to the breakup of the telecommunications monopoly held by American Telegraph and Telephone (AT&T). This breakup coincided with many rapid, major changes in the technology of the telecommunications industry itself.
Until the 1980s telecommunications services were considered to be public services operating within a legislative framework that provided monopoly status in virtually all countries. Along with the development of economic activity, the advent of new technologies has led to the privatization of the telecommunications industry. This trend culminated in the divestiture of AT&T and the deregulation of the US telecommunications system. Similar privatization activities are underway in a number of other countries.
Since 1984, technological advances have produced and expanded telecommunications systems that can provide universal service to all people throughout the world. This occurs as telecommunications technology is now converging with other information technologies. Related fields such as electronics and data processing are involved.
The impact of the introduction of new technology on employment has been mixed. Without question, it has reduced levels of employment and produced the de-skilling of jobs, radically altering the tasks of telecommunications workers as well as the qualifications and experience required of them. However, it is anticipated by some that employment growth will occur in the future as a result of the new business activity stimulated by the deregulated telecommunications industry that will produce many highly skilled jobs.
Occupations within the telecommunications industry can be categorized as either skilled craft or clerical work. Craft jobs include cable splicers, installers, outside plant technicians, central office technicians and frame technicians. These jobs are highly skilled, particularly as a result of the new technological equipment. For example, employees must be very proficient in the electrical, electronics and/or mechanical fields as they relate to the installation, service and maintenance of telecommunications equipment. Training is acquired through classroom and on-the-job training.
Clerical occupations include directory assistance operators, customer service representatives, account representatives and sales clerks. In general these tasks involve the operation of communications equipment such as VDUs private branch exchange (PBX) and facsimile machines which are used to establish local and/or long distance connections, perform business office work inside or outside the workplace and handle sales contacts with customers.
Hazards and Controls
The occupational safety and health hazards within the telecommunications industry can be categorized by the type of tasks or services performed.
Building and construction operations
In general, the same risks occur as in construction and building operations. However, several noteworthy activities which are specific to telecommunications include working at heights on poles or pylons, installing telecommunications wiring systems and excavating for cable laying. The usual means of protection, such as climbing gaffs, safety harnesses, lines and raise platforms and proper shoring for excavations, are applicable in telecommunications. Often, this work is performed during emergency repairs made necessary by storms, landslides or floods.
The safe use of electricity and electrical equipment is extremely important when performing telecommunications work. The normal preventive measures against electrocution, electric shock, short circuits and fires or explosions are fully applicable to telecommunications. Also, a serious source of danger may arise when telecommunications and electricity cables are within close proximity to one another.
Cable laying and maintenance
A significant safety and health concern is cable laying and maintenance. Work on underground cables, pipelines and jointing chambers involves handling heavy cable drums and pulling cables into pipelines with power-driven winches and cable equipment as well as cable splicing or jointing and insulation or waterproofing. During cable splicing and insulation jobs, workers suffer exposure to health hazards such as lead, solvents and isocyanates. Preventive measures include use of the least toxic chemicals, adequate ventilation and PPE. Often, maintenance and repair work is performed in confined spaces like manholes and vaults. Such work necessitates special ventilation equipment, harness and lifting equipment and the provision of a worker stationed above ground who is able to perform emergency cardiopulmonary resuscitation (CPR) and rescue activities.
Another health and safety concern is working with fibre optic telecommunications cables. Fibre optic cables are being installed as an alternative to lead and polyurethane-encased cables because they carry many more communications transmission and they are much smaller in size. Health and safety concerns involve potential burns to the eyes or skin from exposure to the laser beam when cables become disconnected or broken. When this occurs, protective engineering controls and equipment should be provided.
Also, cable installation and maintenance work performed in buildings involves potential exposure to asbestos products. Exposure occurs as a result of the deterioration or break-up of asbestos products like pipes, patching and taping compounds, floor and ceiling tiles and reinforcing fillers in paints and sealants. During the late 1970s, asbestos products were banned or their use was discouraged in many countries. Adherence to a worldwide prohibition will eliminate exposure and resultant health disorders for future generations of workers, but there are still large amounts of asbestos to contend with in older buildings.
Telegraph workers use VDUs and, in some cases, telegraph equipment to perform their work. A frequent hazard associated with this type of work is upper extremity (particularly hand and wrist) musculoskeletal cumulative trauma. These health problems may be minimized and prevented with attention to ergonomic work stations, work environment and work organization factors.
Automatic switching and connecting circuits are the mechanical operations components of modern telecommunications systems. Connections are generally made by microwave and radio frequency waves in addition to cables and wires. Potential hazards are associated with microwave and radio frequency exposures. According to available scientific data, there is no indication that exposure to most types of radiation-emitting telecommunications equipment is directly linked to human health disorders. However, craft employees may be exposed to high levels of radio frequency radiation while working in close proximity to electrical power lines. Data have been collected that suggest a relationship between these emissions and cancer. Further scientific investigations are being conducted to more clearly determine the seriousness of this hazard as well as appropriate prevention equipment and methods. In addition, health concerns have been associated with emissions from cellular telephone equipment. Further research is being conducted to draw conclusions regarding potential health hazards.
The vast majority of telecommunications services are performed with the use of VDUs. Work with VDUs is associated with the occurrence of upper extremity (particularly hand and wrist) musculoskeletal cumulative trauma disorders. Many telecommunications unions, such as the Communications Workers of America (US), Seko (Sweden) and the Communication Workers Union (United Kingdom), have identified catastrophic rates of VDU workplace musculoskeletal cumulative trauma disorders among the workers they represent. Proper design of the VDU workplace with attention to work station, work environment and work organization variables will minimize and prevent these health problems.
Additional health concerns include stress, noise and electrical shock.