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Monday, 04 April 2011 19:04

Falls from Elevations

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Falls from elevations are severe accidents that occur in many industries and occupations. Falls from elevations result in injuries which are produced by contact between the falling person and the source of injury, under the following circumstances:

  • The motion of the person and the force of impact are generated by gravity.
  • The point of contact with the source of injury is lower than the surface supporting the person at the start of the fall.

 

From this definition, it may be surmised that falls are unavoidable because gravity is always present. Falls are accidents, somehow predictable, occurring in all industrial sectors and occupations and having a high severity. Strategies to reduce the number of falls, or at least reduce the severity of the injuries if falls occur, are discussed in this article.

The Height of the Fall

The severity of injuries caused by falls is intrinsically related to the height of fall. But this is only partly true: the free-fall energy is the product of the falling mass times the height of the fall, and the severity of the injuries is directly proportional to the energy transferred during the impact. Statistics of fall accidents confirm this strong relationship, but show also that falls from a height of less than 3 m can be fatal. A detailed study of fatal falls in construction shows that 10% of the fatalities caused by falls occurred from a height less than 3 m (see figure 1). Two questions are to be discussed: the 3-m legal limit, and where and how a given fall was arrested.

Figure 1. Fatalities caused by falls and the height of fall in the US construction industry, 1985-1993

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In many countries, regulations make fall protection mandatory when the worker is exposed to a fall of more than 3 m. The simplistic interpretation is that falls of less than 3 m are not dangerous. The 3-m limit is in fact the result of a social, political and practical consensus which says it is not mandatory to be protected against falls while working at the height of a single floor. Even if the 3-m legal limit for mandatory fall protection exists, fall protection should always be considered. The height of fall is not the sole factor explaining the severity of fall accidents and the fatalities due to falls; where and how the person falling came to rest must also be considered. This leads to analysis of the industrial sectors with higher incidence of falls from elevations.

Where Falls Occur

Falls from elevations are frequently associated with the construction industry because they account for a high percentage of all fatalities. For example, in the United States, 33% of all fatalities in construction are caused by falls from elevations; in the UK, the figure is 52%. Falls from elevations also occur in other industrial sectors. Mining and the manufacturing of transportation equipment have a high rate of falls from elevations. In Quebec, where many mines are steep, narrow-vein, underground mines, 20% of all accidents are falls from elevations. The manufacture, use and maintenance of transportation equipment such as airplanes, trucks and railroad cars are activities with a high rate of fall accidents (table 1). The ratio will vary from country to country depending on the level of industrialization, the climate, and so on; but falls from elevations do occur in all sectors with similar consequences.


Table 1. Falls from elevations: Quebec 1982-1987

                               Falls from elevations                         Falls from elevations in all accidents
                               per 1,000 workers

Construction                        14.9                                                10.1%

Heavy industry                      7.1                                                  3.6%


Having taken into consideration the height of fall, the next important issue is how the fall is arrested. Falling into hot liquids, electrified rails or into a rock crusher could be fatal even if the height of fall is less than 3 m.

Causes of Falls

So far it has been shown that falls occur in all economic sectors, even if the height is less than 3 m. But why do humans fall? There are many human factors which can be involved in falling. A broad grouping of factors is both conceptually simple and useful in practice:

Opportunities to fall are determined by environmental factors and result in the most common type of fall, namely the tripping or slipping that result in falls from grade level. Other falling opportunities are related to activities above grade.

Liabilities to fall are one or more of the many acute and chronic diseases. The specific diseases associated with falling usually affect the nervous system, the circulatory system, the musculoskeletal system or a combination of these systems.

Tendencies to fall arise from the universal, intrinsic deteriorative changes that characterize normal ageing or senescence. In falling, the ability to maintain upright posture or postural stability is the function that fails as a result of combined tendencies, liabilities and opportunities.

Postural Stability

Falls are caused by the failure of postural stability to maintain a person in an upright position. Postural stability is a system consisting of many rapid adjustments to external, perturbing forces, especially gravity. These adjustments are largely reflex actions, subserved by a large number of reflex arcs, each with its sensory input, internal integrative connections, and motor output. Sensory inputs are: vision, the inner ear mechanisms that detect position in space, the somatosensory apparatus that detects pressure stimuli on the skin, and the position of the weight-bearing joints. It appears that visual perception plays a particularly important role. Very little is known about the normal, integrative structures and functions of the spinal cord or the brain. The motor output component of the reflex arc is muscular reaction.

Vision

The most important sensory input is vision. Two visual functions are related to postural stability and control of gait:

  • the perception of what is vertical and what is horizontal is basic to spatial orientation
  • the ability to detect and discriminate objects in cluttered environments.

 

Two other visual functions are important:

  • the ability to stabilize the direction in which the eyes are pointed so as to stabilize the surrounding world while we are moving and immobilize a visual reference point
  • the ability to fixate and pursue definite objects within the large field (“keep an eye on”); this function requires considerable attention and results in deterioration in the performance of any other simultaneous, attention-demanding tasks.

 

Causes of postural instability

The three sensory inputs are interactive and interrelated. The absence of one input—and/or the existence of false inputs—results in postural instability and even in falls. What could cause instability?

Vision

  • the absence of vertical and horizontal references—for example, the connector at the top of a building
  • the absence of stable visual references—for example, moving water under a bridge and moving clouds are not stable references
  • the fixing a definite object for work purposes, which diminishes other visual functions, such as the ability to detect and discriminate objects that can cause tripping in a cluttered environment
  • a moving object in a moving background or reference—for example, a structural steel component moved by a crane, with moving clouds as background and visual reference.

 

Inner ear

  • having the person’s head upside down while the level equilibrium system is at its optimum performance horizontally
  • travelling in pressurized aircraft
  • very fast movement, as, for example, in a roller-coaster
  • diseases.

 

Somatosensory apparatus (pressure stimuli on the skin and position of weight-bearing joints)

  • standing on one foot
  • numbed limbs from staying in a fixed position for a long period of time—for example, kneeling down
  • stiff boots
  • very cold limbs.

 

Motor output

  • numbed limbs
  • tired muscles
  • diseases, injuries
  • ageing, permanent or temporary disabilities
  • bulky clothing.

 

Postural stability and gait control are very complex reflexes of the human being. Any perturbations of the inputs may cause falls. All perturbations described in this section are common in the workplace. Therefore, falling is somehow natural and prevention must therefore prevail.

Strategy for Fall Protection

As previously noted, the risks of falls are identifiable. Therefore, falls are preventable. Figure 2 shows a very common situation where a gauge must be read. The first illustration shows a traditional situation: a manometer is installed at the top of a tank without means of access In the second, the worker improvises a means of access by climbing on several boxes: a hazardous situation. In the third, the worker uses a ladder; this is an improvement. However, the ladder is not permanently fixed to the tank; it is therefore probable that the ladder may be in use elsewhere in the plant when a reading is required. A situation such as this is possible, with fall arrest equipment added to the ladder or the tank and with the worker wearing a full body harness and using a lanyard attached to an anchor. The fall-from-elevation hazard still exists.

Figure 2. Installations for reading a gauge

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In the fourth illustration, an improved means of access is provided using a stairway, a platform and guardrails; the benefits are a reduction in the risk of falling and an increase in the ease of reading (comfort), thus reducing the duration of each reading and providing a stable work posture allowing for a more precise reading.

The correct solution is illustrated in the last illustration. During the design stage of the facilities, maintenance and operation activities were recognized. The gauge was installed so that it could be read at ground level. No falls from elevations are possible: therefore, the hazard is eliminated.

This strategy puts the emphasis on the prevention of falls by using the proper means of access (e.g., scaffolds, ladders, stairways) (Bouchard 1991). If the fall cannot be prevented, fall arrest systems must be used (figure 3). To be effective, fall arrest systems must be planned. The anchorage point is a key factor and must be pre-engineered. Fall arrest systems must be efficient, reliable and comfortable; two examples are given in Arteau, Lan and Corbeil (to be published) and Lan, Arteau and Corbeil (to be published). Examples of typical fall prevention and fall arrest systems are given in table 2. Fall arrest systems and components are detailed in Sulowski 1991.

Figure 3. Fall prevention strategy

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Table 2. Typical fall prevention and fall arrest systems

 

Fall prevention systems

Fall arrest systems

Collective protection

Guardrails Railings

Safety net

Individual protection

Travel restricting system (TRS)

Harness, lanyard, energy absorber anchorage, etc.

 

The emphasis on prevention is not an ideological choice, but rather a practical choice. Table 3 shows the differences between fall prevention and fall arrest, the traditional PPE solution.

Table 3. Differences between fall prevention and fall arrest

 

Prevention

Arrest

Fall occurrence

No

Yes

Typical equipment

Guardrails

Harness, lanyard, energy absorber and anchorage (fall arrest system)

Design load (force)

1 to 1.5 kN applied horizontally and 0.45 kN applied vertically—both at any point on the upper rail

Minimum breaking strength of the anchorage point

18 to 22 kN

Loading

Static

Dynamic

 

For the employer and the designer, it is easier to build fall prevention systems because their minimum breaking strength requirements are 10 to 20 times less than those of fall arrest systems. For example, the minimum breaking strength requirement of a guard rail is around 1 kN, the weight of a large man, and the minimum breaking strength requirement of the anchorage point of an individual fall arrest system could be 20 kN, the weight of two small cars or 1 cubic metre of concrete. With prevention, the fall does not occur, so the risk of injury does not exist. With fall arrest, the fall does occur and even if arrested, a residual risk of injury exists.

 

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More in this category: « Rollover Confined Spaces »

Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides