Theory Of Accident Causation

Theory of Accident Causation

1. Heinrich’s Theory Of Accident Causation

H.W. Heinrich, a pioneer in safety philosophy, firstly published his work, Industrial Accident Prevention, in 1931.

Many of his principles and basic philosophy for theory of accident causation and prevention are confirmed by time and application.

Some are also questioned and criticized. His philosophy is based on his 10 axioms (self evident truths) accordingly as follows.

The occurrence of an injury invariably results from a completed sequence of factors – the last one of these being the accident itself. The accident in turn in invariably caused or permitted directly by the unsafe act of a person and/or a mechanical or physical hazard subsequently.

The unsafe acts of persons are responsible for a majority of accidents accordingly.

The persons who suffers a disabling injury caused by an unsafe act, in the average case has had over 300 narrow escapes from serious injury as a result of committing the very same unsafe act. Likewise, persons get exposure to mechanical hazards hundreds of times before they suffer injury.

The severity of an injury is largely fortuitous – the occurrence of the accident that results in injury is largely preventable similarly.

The four basic motives or reasons for the occurrence of unsafe acts provide a guide to the selection of appropriate corrective measures.

There are:
Improper attitude, Lack of knowledge or skill, Physical unsuitability and Improper mechanical or physical environment likewise.

Still, Four basic methods are available for preventing accidents. These are Engineering revision, Persuasion and appeal, Personnel adjustment and Discipline.

Although, Methods of most value in accident prevention are analogous with the methods require for the control of the quality, cost and quantity of production.

Management has the best opportunity and ability to initiate the work of prevention, therefore it should assume the responsibility.

Moreover, The supervisor or foreman is the key man in individual accident prevention. In the same vein, his application of the art of supervision for the control of work performance is the factor of greatest influence in successful accident prevention. It can be expressed and taught as a simple four step formula – Identity the problem, find and verify the reason for the existence of the problem, select the appropriate remedy and apply the remedy.

In short, supplementation of the humanitarian incentive for preventing accidental injury by two powerful economic factors :
(1) The safe establishment is efficiency productive and the unsafe establishment is inefficient accordingly,
(2) The direct employer’s cost of industrial injuries for compensation claims and for medical treatment is about one-fifth of the total (direct plus indirect) cost which the employer must pay subsequently.

These axioms were the first set of principles or guidelines ever set before in industrial safety and it has guided all safety activity till today.

During the passage of years, some of his axioms are questioned and disbelieved as truths.

But, most of them are still true and deal with the important areas of safety, viz. accident causation and prevention, reasons of unsafe acts and conditions, management control functions, responsibility of organization, costs of accident, safety and productivity etc.

Accident Sequence:

  • The five factors in accident occurrence series in chronological order furthermore:
  1. Ancestry and social environment.
  2. Fault of person.
  3. Unsafe act and/or mechanical or physical hazard.
  4. Accident and
  5. Injury.
  • One factor is dependent on another and one follows because of another, thus constituting a sequence comparison with a row of dominoes place on end and in such alignment in relation to one another that the first domino precipitates that fall of the entire row.
  • An accident is merely one factor in the sequence. If interruption of this series by the elimination or withdrawal or even one of the five factors that comprise it, we can possibly prevent the injury.
  • In above dominos, social environment includes family and surrounding atmosphere in which a person is born and brought up.

This is origin or root cause of behavioral development as per H. W. Heinrich.

  • Undesirable traits include unsafe behaviour, negligence, lack of knowledge, violent temper, nervousness, recklessness etc.
  • Unsafe act or conditions are the results of undesirable traits.
  • Causation of an accident because of unsafe act or condition or both.
  • Injury is the result of accident.

This suggests the steps of management controls as under:

Steps of Management Controls for Heinrich`s Theory Of Accident Causation
Steps of Management Controls for Heinrich`s Theory Of Accident Causation

From other similar studies, Heinrich concludes, that “all agree in general that man failure is predominantly the proximate and direct cause of industrial accident.

The economic Times, Mumbai, of 21/9/97 gave following figures of Railway accidents:

Failure of Railway Staff363358351237249
Failure of other persons6072767159
Other causes10190748873

Criticism of Heinrich’s Theory of accident causation and His Reply:

H.W. Heinrich’s ratio theory (fact finding from a study of 75000 accident cases) that 88% accidents are due to unsafe acts, 10 % due to unsafe conditions and 2 % unpreventable have criticism as follows:

  • Heinrich made his analysis from reports submitted to insurers by the managers of the companies at which the accidents happened. No manager would want to indicate to the insurer or to the safety authority or agency that the company had been at fault and that hazards existed in the workplace under his control. Such a statement may sound harsh but is borne by known practices, which also distort statistical data.
  • This ratio idea is fallacious because it rests on a false assumption that accidents are result of either unsafe acts or unsafe conditions. Besides there are multiple (combined) factors as supported by the results stated below.
  • A study conducted by the National Safety Council (USA) yielded the following conclusions:
    18% injuries due to mechanical causes.
    19% injuries due to personal causes.
    63% due to a combination of both causes.
  • A study by the Department of Labor & Industry of the State of Pennsylvania yielded the following:
    3% due to mechanical causes.
    2% due to unsafe acts.
    95% due to a combination of both causes.

The ratio idea had done much harm and many employers still say, ‘why should first of all we spend a lot of money on only 10% mechanical causes? We will start after removal of 88% personal causes by the employees’. Hence, Such concept is damaging.

  • There are two essentials in every case of injury – there must be some degree of hazard and there must also be faulty behaviour by someone. If detection and eliminaton of the factor of hazard properly, there could be no injury.
  • Similarly, if behaviour could be made and kept perfect, the result would be the same. However, these are the duties of every management.
  • Identically, It must try collectively to combat the combined causes of accident and should not separate the unsafe acts as employee’s responsibility only.
  • However, Law always stresses for employer’s responsibility first. Why? Because the primary duty, money and ultimate control lie with the management to detect and remove unsafe conditions actions and to give necessary training to the workers. Even though, this is the only safe and healthy approach.
  • Heinrich is aware about the public debate and criticism of his 88-10-2% ratio in accident causation stated above and its wide spread that may influence people to ignore the machine guarding and to take the assumedly easier path of issuing instructions.
  • In reply, he states his belief that the accident-prevention fraternity, like almost all professional groups, wants all the pertinent facts and he has more faith in their good judgement than to fear that they will ignore the very first common-sense step of safeguarding mechanical environment.
  • The machine is dangerous as man makes it so. It’s man’s use of the machine – more correctly, his abuse of it – that creates danger.
  • He points out that judgement must be used in selecting the major cause when a mechanical hazard and an unsafe act both contribute to accident occurrence.
  • Personal judgement may lead to error, but it is defensible and in the majority of cases results in fair conclusions.
  • The 300-29-1 ratio (Foundation of lost-time accident) – Explaining the foundation of a major injury, Heinrich estimates that in a unit group of 330 accidents of the same kind and involving the same person, 300 result in no injuries, 29 in minor injuries and 1 in a major lost-time injury.
  • He explains this 300-29-1 ratio as an aid in accident prevention, because, it vividly emphasizes preventive opportunity, when an employee, either because of his repeated unsafe action or repeated exposure to an unsafe mechanical condition, suffers 300 no-injury accidents (actual events such as slips and falls but fortunately not causing injury) surely there can be no lack of opportunity in preventive effort.
  • Replying misunderstanding and misquotation of this ratio, he states that this ratio is an average. Sometimes a major or serious injury occurs the very first time a person acts unsafely or there is exposure to mechanical hazard – in other cases he is so endangered hundreds or thousand of times and may slip or fall many times before injury is sustained. In industry, where employees are under supervision, these unsafe practices, conditions and the resulting narrow escapes from actual injury (events-accidents) are tangible and visible. They can and control long before one of the 300 no-injury accidents ultimately causes an injury.
  • In above ratio – cases, a major injury is any report case to insurance office or to the State Compensation Commissioner. A minor injury is a scratch, bruise, or laceration such as is commonly termed a first-aid case. A no-injury accident is an unplanned event involving the movement of a person or an object, ray or substance (slip, fall, flying object, inhalation etc.) having the probability of causing personal injury or property damage but not resulted in injury (near miss).
  • Safety and Productivity – Citing the study made by the Committee on Safety and Production of the American Engineering Council, Heinrich has narrated the detail findings, some of which are given below:
  1. Control of Industrial accidents under modern conditions of highly efficient productivity.
  2. Efforts to improve safety performance do not interfere with production.
  3. Security of Maximum productivity is ordinary only when the accident performance tends toward the irreducible minimum.
  4. The cost of accidents is a loss in industrial operation, which we should not neglect.

2. Frank Bird’s Domino Theory Of Accident Causation

Updation of Heinrich’s theory of domino sequence by Frank Bird Jr. to explain the circumstances that lead to losses (injury) in the chronological order of five dominos:

Lack of control is the first domino and refers the fourth function of the management (planning, organizing, directing, controlling and coordinating). It involves accident investigation, facility inspection, job analysis, personal communication, selection and training, ‘standards’ in each work activity identified, measuring performance by standards and correcting performance by improving the existing programmes. This first domino may fall due to inadequate standards, programmes and follow up.

Basic Causes (origins) are (1) Personal factors – lack of knowledge or skill, improper motivation and physical or mental problems and (2) job factors – inadequate work standards, design, maintenance, purchasing standards, abnormal usage etc. These basic causes are origin of substandard acts and conditions and failure to identity them permits the second domino to fall, which initiates the possibility of further chain reaction.

Immediate causes are only symptoms of the underlying problem. They are substandard practices or conditions (known as unsafe acts and unsafe conditions) that could cause the fourth domino to fall. These causes should be identified, classified and removed by appropriate measures.

Accident or incident is the result of unsafe acts or / and unsafe conditions. This point is the contact stage. Some counter conditions employed are deflection, dilution, reinforcement, surface modification, segregation, barricading, protection, absorption, shielding etc.

Injury includes traumatic injury, diseases and adverse mental neurological or systematic effects resulting form workplace exposures. ‘Damage’ includes all types of property damage including fire. The severity of losses involving physical harm and property damage can be minimized by prompt reparative action, salvage in the case of property damage and fire control devices and trained personnel.

Frank E Bird, in 1969, analyzed 1753498 accidents reported by 297 companies of America. His conclusion is shown in Fig.

Frank-E-Bird-pyramid for theory of accident causation
Frank-E-Bird-pyramid for theory of accident causation
  • Inference of this 1-10-30-600 ratio is that 630 no-injury accidents, with 10 minor and 1 major (serious) injury accidents, provide a much larger basis for many opportunities to prevent any injury accident. Out of total 641 events, only 10 may result in minor injuries and only 1 in major injury. But this can happen at any time not necessarily at the end.

3. V. L. Grose’s Multiple Causation Theory Of Accident Causation:

  • As per this theory many contributing factors combine together in random fashion, causing accidents. Such should be identified. Mostly man, machine and media interact with each other to generate causes for accident and management has to identify them and provide necessary safety measures.

In this theory –

  1. Man includes – Workers, public etc.
  2. Machine includes – equipment, vehicle etc.
  3. Media includes – environment, weather, roadways etc.
  4. Management means within which above three parameters operate i.e. to be controlled by the management.

Characteristics of –

  1. Man includes – age, sex, height, skill level, training, motivation etc.
  2. Machine includes – size, weight, speed, shape, material of constriction, energy etc.
  3. Media includes – pressure, temperature, content, contaminants, obstruction on road etc.
  4. Management includes – structure, style, policy, procedure, communication etc.

Simple example of this theory is a man slipping due to walking on a banana skin lying on the road. Here main contributing factors are as under:

  • Man – A man walking on the road.
  • Machine or object vehicle – Slippery banana skin.
  • Media – Hard road.
  • All above causes are interacting with each other to lead to the accident. Absence of any one cause can avoid the accident. This indicates that slippery banana skin should be removed from the road or man should be more attentive for not walking on it or the road should not be hard to cause slipping.
  • Let us take another example of a worker falling from a ladder. As per the domino theory an investigation is as under:
The unsafe actClimbing the defective ladder
The unsafe conditionThe defective ladder
The remedial measureRemove or repair the defective ladder and train that worker
  • As per the multiple causation theory some of the contributing factors surrounding this accident can be found out by asking:
  1. Why was the defect in ladder not found in normal (past) inspections?
  2. Why did the supervisor allow its use? Why did he not get it repaired urgently?
  3. Didn’t the injured worker know he shouldn’t use it?
  4. Was he properly trained or not?
  5. Was he reminded or cautioned?
  6. Did the supervisor examine the job first?
  • The answers to these and similar questions would suggest the following measures:
  1. An improved inspection procedure.
  2. Repairing the ladder (machine, tool, job etc.) immediately i.e. not waiting for an accident.
  3. Improved training and supervision.
  4. Better fixation of responsibilities.
  5. Pre job planning and checking by supervisors.
  • Thus application of the multiple causation theory leads us to deep causation analysis and improved management systems are suggested to eradicate the problem from its origin. The range and depths of the multiple causation factors provide much detail of long-run safety measures.

4. Energy (Release) Theory Of Accident Causation:

  1. Change the rate of release or distribution of released energy e.g. reduce the road slope, use inhibitor to reduce rate of reaction, sprinkler to reduce rate of burning, scrubber to scrub toxic gas, condenser to liquefy organic vapour.
  2. Divert (separate) the energy released in time or space. e.g. separate paths for vehicles and pedestrian traffic, keep electric wiring or pesticide out of reach, discharge gases at height.
  3. Provide barrier between the energy released and a structure or a person likely to be affected. e.g. guards on machines, radiation shield, filter, safety goggles, earplugs, insulation on hot surface, blast wall against explosion energy.
  4. Make the surfaces of structure safe. e.g. rounded corners, blunt objects, big handles of tools and no sharp edges.
  5. Strengthen the structure or person susceptible to damage. e.g. fire resistant wall, training to workers and vaccination for disease.
  6. Early detection of damage and actuate counter effect. e.g. fire detectors with sprinkles, high level alarm and tripping of feed pump, temperature alarm and starting of cooling system.
  7. Speedy measures to restore normal condition. e.g. rehabilitation of injured worker, repairing of a damaged machine or vehicle.