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Thursday, 31 March 2011 15:09

Theoretical Principles of Job Safety

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This presentation covers the theoretical principles of job safety and the general principles for accident prevention. The presentation does not cover work-related illnesses, which, although related, are different in many respects.

Theory of Job Safety

Job safety involves the interrelationship between people and work; materials, equipment and machinery; the environment; and economic considerations such as productivity. Ideally, work should be healthful, not harmful and not unreasonably difficult. For economic reasons, as high a level of productivity as possible must be achieved.

Job safety should start in the planning stage and continue through the various phases of production. Accordingly, requirements for job safety must be asserted before work begins and be implemented throughout the work cycle, so that the results can be appraised for purposes of feedback, among other reasons. The responsibility of supervision toward maintaining the health and safety of those employed in the production process should also be considered during planning. In the manufacturing process, people and objects interact. (The term object is used in the broader sense as expressed in the customary designation “people-(machine)-environment system”. This includes not only technical instruments of work, machines and materials, but all surrounding items such as floors, stairs, electrical current, gas, dusts, atmosphere and so on.)

Worker-Job Relationships

The following three possible relationships within the manufacturing process indicate how personal injury incidents (especially accidents) and harmful working conditions are unintended effects of combining people and the objective working environment for the purpose of production.

  1. The relationship between the worker and the objective working environment is optimal. This means well-being, job safety and labour-saving methods for the employees as well as the reliability of the objective parts of the system, like machines. It also means no defects, accidents, incidents, near misses (potential incidents) or injuries. The result is improved productivity. 
  2. The worker and the objective working environment are incompatible. This may be because the person is unqualified, equipment or materials are not correct for the job or the operation is poorly organized. Accordingly, the worker is unintentionally overworked or underutilized. Objective parts of the system, like machines, may become unreliable. This creates unsafe conditions and hazards with the potential for near misses (near accidents) and minor incidents resulting in delays in production flow and declining output.
  3. The relationship between the worker and the objective working environment is completely interrupted and a disruption results, causing damage, personal injury or both, thereby preventing output. This relationship is specifically concerned with the question of job safety in the sense of avoiding accidents.


Principles of Workplace Safety

Because it is apparent that questions of accident prevention can be solved not in isolation, but only in the context of their relationship with production and the working environment, the following principles for accident prevention can be derived:

  1. Accident prevention must be built into production planning with the goal of avoiding disruptions.
  2. The ultimate goal is to achieve a production flow that is as unhindered as possible. This results not only in reliability and the elimination of defects, but also in the workers’ well-being, labour-saving methods and job safety.


Some of the practices commonly used in the workplace to achieve job safety and which are necessary for disruption-free production include, but are not limited to the following:

  • Workers and supervisors must be informed and aware of the dangers and potential hazards (e.g., through education).
  • Workers must be motivated to function safely (behaviour modification).
  • Workers must be able to function safely. This is accomplished through certification procedures, training and education.
  • The personal working environment should be safe and healthy through the use of administrative or engineering controls, substitution of less hazardous materials or conditions, or by the use of personal protective equipment.
  • Equipment, machinery and objects must function safely for their intended use, with operating controls designed to human capabilities.
  • Provisions should be made for appropriate emergency response in order to limit the consequences of accidents, incidents and injuries.


The following principles are important in understanding how accident prevention concepts relate to disruption-free production:

  1. Accident prevention is sometimes considered a social burden instead of a major part of disruption prevention. Disruption prevention is a better motivator than accident prevention, because improved production is expected to result from disruption prevention.
  2. Measures to ensure workplace safety must be integrated into the measures used to ensure disruption-free production. For example, the instructions on hazards must be an integral part of the general directions governing the flow of production at the workplace.


Accident Theory

An accident (including those that entail injuries) is a sudden and unwanted event, caused by an outside influence, that causes harm to people and results from the interaction of people and objects.

Often the use of the term accident in the workplace is linked with personal injury. Damage to a machine is often referred to as a disruption or damage, but not an accident. Damage to the environment is often called an incident. Accidents, incidents and disruptions which do not result in injury or damage are known as “near accidents” or “near misses”. So while it may be considered appropriate to refer to accidents as cases of injury to workers and to define the terms incident, disruption and damage separately as they apply to objects and the environment, in the context of this article they will all be referred to as accidents.

The conceptual model for the term accident indicates that workplace accidents occur from workers and objects interacting with each other through the release of energy. The cause of an accident can lie in the characteristics of the injured worker (e.g., not capable of performing the work safely) or of the object (e.g., unsafe or unsuitable equipment). The cause can also be another worker (providing erroneous information), supervisor (receiving incomplete job instructions) or trainer (receiving incomplete or incorrect training). The following can be derived for accident prevention:

Assuming that workers as well as their objective environments can be carriers of hazards or dangers, accident prevention would basically consist of eliminating the hazards or dangers, or impeding the consequences by keeping the carriers apart or by minimizing the effects of the energy.

Potential Hazards and Risks

Although a hazard or danger may exist in an object, if the worker and the object are so separate from one another that they cannot come into contact, no accident is possible. For example, if the object has a potential hazard (e.g., a suspended load is moved by a crane), this potential hazard cannot cause an injury so long as there are no people in the effective area of the suspended load. It is only when a worker comes into the area of the crane’s suspended load that an actual hazard or danger to this worker is posed, because an interaction between the worker and the object is possible. It should be noted that objects can also endanger other objects, such as vehicles parked under the crane’s load. Risk, defined as a means of quantifying the hazard, is the product of the anticipated frequency of the damage and the anticipated scope of the damage. Accident risk is correspondingly the product of the anticipated frequency of accidents (relative accident frequency) and anticipated accident severity. Relative accident frequency is the number of accidents per risk-time (accidents per 1 million hours or injuries per work year). The seriousness of the accident can be shown quantitatively with the lost time (e.g., lost work days), class of injury (minor accident or first aid case, reportable injury, lost-time compensation case and fatal accident), type of injury, and cost of injury. This risk data should be recorded empirically and in terms of a theoretical prognosis.

The risks of accidents are different in various workplaces, under various conditions. For example, the risks involved in drilling for oil, using the same workers and identical equipment, differ widely depending on the geography (drilling on land or off shore) and the climate (Arctic exploration or deserts). The level of accident risk depends on:

  • the anticipated frequency of error of the worker and the technology (number per 1 million hours, etc.)
  • the probability of the errors resulting in accidents (accident: error = 1:x)
  • the probability of the seriousness level of the accident.

The acceptance of accident risks also varies widely. High accident risk appears to be acceptable in road traffic whereas a zero base tolerance is expected in the field of nuclear energy. For purposes of accident prevention, it therefore follows that the driving force is the smallest possible acceptance of accident risk.

Causes of Accidents

The occurrence of an accident requires classification on a scale from cause to effect. Three levels must be differentiated:

  • the level of the causes of possible and actual accidents
  • the level of the accident’s origins
  • the level of the accident’s consequences in the form of personal and material damages.

Cause is the reason for the accident. Almost every accident has multiple causes such as hazardous conditions, combinations of factors, courses of events, omissions and so on. For example, causes of an accident involving a burst boiler may include one or a combination of the following reasons: faulty materials in the boiler wall, inadequate training to ensure safe operation, failure of a pressure relief device, or violation of an operating procedure such as overheating. Without one or more of these deficiencies, an accident may not have happened. Other conditions, which are not causal to the accident, should be separated. In the case of the burst boiler, these would include conditions such as information about the time, the ambient temperature and the size of the boiler room.

It is important to differentiate the factors associated with the production process from the accident causes linked to workers (conduct of the immediate operator), the organization (safe work procedures or policies) and technical accident causes (environmental changes and object failures). However, in the final analysis, every accident results from faulty conduct of people, because people are always at the end of the causal chain. For example, if faulty material is determined to be the cause of a boiler bursting, then improper conduct existed either on the part of the builder, manufacturer, tester, installer or owner (e.g., corrosion due to inadequate maintenance). Strictly speaking, there is no such thing as a “technical failure” or technical accident cause. The technology is only the intermediate link to the consequences of the improper conduct. Nevertheless, the normal division of causes into behavioural, technical and organizational is useful, because this points toward which group of people behaved improperly and also helps select the appropriate corrective measures.

As previously stated, most accidents are the result of a combination of causes.

For example, a person slips on an oil spot in a dark, unlighted passageway and hits the sharp edge of a replacement part that is lying there, resulting in a head injury. The immediate causes of the accident are inadequate lighting in the passageway, unsafe floor (oil spot), inadequately skid-free shoe soles, not wearing head protection, and the replacement part not in its proper place. The accident could not have happened if the combination of causes had been eliminated or the causal chain had been broken. Successful accident prevention therefore consists of recognizing the causal chain that leads to an accident and breaking it, so that the accident can no longer occur.

Effect of Strains and Demands

Mechanization and automation of production processes have advanced considerably in recent years. It may appear that the causes of many accidents have shifted from human error to those related to the maintenance of and interface with automated processes. However, these positive consequences of technology are counterposed to other, negative ones, particularly the increase in psychological strains and corresponding ergonomic physical demands on workers in automated plants due to the increased attention and responsibility required for overseeing the automated operations process, impersonal working environment and monotony of work. These strains and corresponding demands increase the occurrence of accidents and can be harmful to health.

  1. Strains are effects on workers which originate in the workplace, such as environmental strains (temperature, heat, humidity, light, noise and air pollution), or they can be static or dynamic strains originating directly from the work process (lifting, climbing, chemical exposure and so on). Strain levels can be physically measured (noise, force, atmospheric exposures and so on), whereas strain factors are physically unmeasurable influences (fatigue, mental stress, plant worker/management relationships and so on).
  2. Demands on workers are dependent on the type and degree of the strain as well as differing individual capability to withstand the strain. Effects of demands show up physically and psychologically in the human body. The effects of the demands can be desirable or undesirable, depending on the type and degree. Undesirable effects, such as physical and psychological exhaustion, work aggravations, illness, lack of coordination and concentration, and unsafe behaviour cause increased risk of accident.

For purposes of accident prevention, it follows that workers, based on their individual competencies, capabilities and willingness, should be able to physically and psychologically work safely provided that there are no outside factors such as unsuitable equipment, poor environment or unsatisfactory work conditions. Safety may be improved by organizing the work process to include appropriate stimuli such as planned job changes, expansion of work and tasks, and work enrichment.

Near Accidents (Near Misses)

A large part of production loss results from disruptions in the form of near misses (near accidents), which are the basis of occurrences of accidents. Not every disruption affects work safety. Near accidents (near misses) are those occurrences or incidents in which no injury or damage resulted, but if injury or damage had occurred, they would be classified as accidents. For example, a machine that unexpectedly stops running without damage to the equipment or work is considered to be a near accident. Additionally, the disruption may cause another near accident if the machine suddenly starts up again while a worker is inside trying to determine the cause of the stoppage, but the worker is not injured.

Accident Pyramid

Accidents are relatively rare occurrences, and usually the more serious the accident, the more rare the occurrence. Near accidents form the bottom, or base, of the accident pyramid, whereas fatal accidents stand at the top. If lost time is used as a criterion for the seriousness of accidents, we find a relatively high degree of correspondence with the accident pyramid. (There may be a slight deviation as a result of the reporting requirements of different countries, companies and jurisdictions.)

The accident pyramid can be very different for individual types or classifications of accidents. For example, accidents involving electricity are disproportionately serious. When accidents are classified by occupation, we see that certain types of work activities suffer disproportionately more serious accidents. In both cases the accident pyramid is top-heavy due to the relatively high proportion of serious and fatal accidents.

From the accident pyramid, it follows for purposes of accident prevention that:

  1. Accident prevention begins with avoiding near accidents (near misses).
  2. Eliminating minor accidents usually has a positive effect on eliminating serious accidents.


Accident Prevention

The different paths of accident prevention for ensuring workplace safety are as follows:

  1. Eliminate the hazard or danger so that injury or damage is no longer possible.
  2. Provide for separation between the worker (or equipment) and the hazard (equal to elimination of the hazard). The danger remains, but an injury (or damage) is not possible since we make sure that the natural zones of influence of workers (equipment) and object (hazard or danger) do not intersect.
  3. Provide shielding, such as fireproofing, protective clothing and respirators to minimize the hazard. The hazard still exists, but the possibility of an injury or damage is reduced by minimizing the chances of the hazard having an effect by shielding the danger.
  4. Adapt to the hazard by providing measures such as warning systems, monitoring equipment, information about dangers, motivation for safe behaviour, training and education.



In 1914, Max Planck (German physicist, 1858–1947) said: “In every science the highest watchword is the task of seeking order and continuity from the abundance of individual experiences and individual facts, in order, by filling the gaps, to integrate them into a coherent view.” This principle also applies to the complex scientific and practical questions of job safety because they not only interface with many different disciplines, but also are themselves multifaceted. While it is difficult, for this reason, to systematize the many problems involved with job safety, it is necessary to properly organize the individual questions according to significance and context, and to pose effective options for improving job safety.



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