2.0 Accident Causation Theories

To better identify the causes for accidents, one should be familiar with the various accident investigation theories that have been developed over the years to describe how accidents occur.  Accident causation theories have evolved from the Domino Theory of the 1930's to today's more popular multiple causation theories for accidents.

2.1 The Domino Theory

According to W. H. Heinrich (1931), who developed the so-called Domino Theory, 88% of all accidents are caused by unsafe acts of people, 10% by unsafe actions and 2% by "acts of God." He proposed a "five-factor accident sequence" in which each factor would actuate the next step in the manner of toppling dominoes lined up in a row. The sequence of accident factors is as follows:

  1. Ancestry and social environment

  2. Worker fault

  3. Unsafe act together with mechanical and physical hazard 

  4. Accident 

  5. Damage or injury

In the same way that the removal of a single domino in the row would interrupt the sequence of toppling, Heinrich suggested that removal of one of the factors would prevent the accident and resultant injury; with the key domino to be removed from the sequence being number 3. One downside to this theory is the fact that Heinrich provided no data for his theory and data analysis of accidents indicate that the percentages provided by Heinrich vary greatly across industries and occupations.  Today, the safety profession does not promote Heinrich's accident causation theory as being valid.  However, it represents a starting point for the evolution of accident causation theories.

The Domino Theory

The Domino Theory

2.2 The Pure Chance Theory

According to the Pure ChanceTheory, every one of any given set of workers has an equal chance of being involved in an accident. It further implies that there is no single discernible pattern of events that leads to an accident. In this theory, all accidents are treated as corresponding to Heinrich’s acts of God, and it is held that there exist no interventions to prevent them.

The Pure Chance Theory

The Pure Chance Theory

2.3 The Biased Liability Theory

Biased Liability Theory is based on the view that once a worker is involved in an accident, the chances of the same worker becoming involved in future accidents are either increased or decreased as compared to the rest of workers. This theory contributes very little, if anything at all, towards developing preventive actions for avoiding accidents.

2.4 The Accident Proneness Theory

Accident Proneness Theory maintains that within a given set of workers, there exists a subset of workers who are more liable to be involved in accidents. Researchers have not been able to prove this theory conclusively because most of the research work has been poorly conducted and most of the findings are contradictory and inconclusive. This theory is not generally accepted. It is felt that if indeed this theory is supported by any empirical evidence at all, it probably accounts for only a very low proportion of accidents without any statistical significance.

2.5 The Energy Transfer Theory

Practice Exercise

This ungraded exercise will help you review the material in this section.

The most acceptable accident causation theory used by today's safety professional is:

Those who accept the Energy Transfer Theory put forward the claim that a worker incurs injury or equipment suffers damage through a change of energy, and that for every change of energy there is a source, a path, and a receiver. This theory is useful for determining injury causation and evaluating energy hazards and control methodology. Strategies can be developed which are either preventive, limiting, or ameliorating with respect to the energy transfer.

Control of energy transfer at the source can be achieved by the following means:

The path of energy transfer can be modified by:

The receiver of energy transfer can be assisted by adopting the following measures:

2.6 The Multiple Causation Theory

Multiple Causation Theory is an outgrowth of the Domino Theory, but it postulates that for a single accident there may be many contributory factors, causes and sub-causes, and that certain combinations of these give rise to accidents. According to this theory, the contributory factors can be grouped into the following two categories:

  1. Behavioral. This category includes factors pertaining to the worker, such as improper attitude, lack of knowledge, lack of skills, and inadequate physical and mental condition.
  2. Environmental. This category includes improper guarding of other hazardous work elements and degradation of equipment through use and unsafe procedures.

The major contribution of this theory is to bring out the fact that rarely, if ever, is an accident the result of a single cause or act.

Multiple Causation Theory

Multiple Causation Theory