THEORY OF ACCIDENT CAUSES
Accidents are defined as unplanned
occurrences which result in injuries, fatalities, loss of production or damage
to property and assets. Preventing accidents is extremely difficult in the
absence of an understanding of the causes of accidents. Many attempts have been
made to develop a prediction theory of accident causation, but so far none has
been universally accepted. Researchers from different fields of science and
engineering have been trying to develop a theory of accident causation which
will help to identify, isolate and ultimately remove the factors that
contribute to or cause accidents. In this article, a brief outline of various
accident causation theories is presented, followed by a structure of accidents.
Accident Causation Theories
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.
Although Heinrich provided no data for his theory, it nonetheless represents a
useful point to start discussion and a foundation for future research.
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:
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.
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.
The pure chance
theory
According to the pure chance theory, 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.
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.
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.
The energy transfer
theory
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:
· Elimination of the source
· Changes made to the design or specification
of elements of the work station
· Preventive maintenance.
The path of energy transfer can be modified
by:
· Enclosure of the path
· Installation of barriers
· Installation of absorbers
· Positioning of isolators.
The receiver of energy transfer can be
assisted by adopting the following measures:
· Limitation of exposure
· Use of personal protective equipment.
The “symptoms
versus causes” theory
The “symptoms versus causes” theory is not so
much a theory as an admonition to be heeded if accident causation is to be understood.
Usually, when investigating accidents, we tend to fasten upon the obvious
causes of the accident to the neglect of the root causes. Unsafe acts and
unsafe conditions are the symptoms-the proximate causes-and not the root causes
of the accident.
Structure of Accidents
The belief that accidents are caused and can
be prevented makes it imperative for us to study those factors which are likely
to favour the occurrence of accidents. By studying such factors, the root
causes of accidents can be isolated and necessary steps can be taken to prevent
the recurrence of the accidents. These root causes of accidents can be grouped
as “immediate” and “contributing”. The immediate causes are unsafe acts of the
worker and unsafe working conditions. The contributing causes could be
management-related factors, the environment and the physical and mental
condition of the worker. A combination of causes must converge in order to
result in an accident.
Below figure shows the structure of accidents, including the details of immediate
causes, contributing causes, types of accidents and results of accidents. This
accounting is not exhaustive by any means. However, an understanding of the
“cause and effect” relation of the accident-causing factors is required before
continuous improvement of safety processes can be undertaken.
Structure of accidents
Summary
Accident causation is very complex and must
be understood adequately in order to improve accident prevention. Since safety
lacks a theoretical base, it cannot be regarded as being a science yet. This
fact should not discourage us, as most of the scientific
disciplines-mathematics, statistics and so on-passed through a similarly
tentative phase at one time or the other. Accident causation study holds great
promise for those who are interested in developing the pertinent theory. At
present, theories of accident causation are conceptual in nature and, as such,
are of limited use in preventing and controlling accidents. With such a
diversity of theories, it will not be difficult to understand that there does
not exist one single theory that is considered right or correct and is
universally accepted. These theories are nonetheless necessary, but not
sufficient, for developing a frame of reference for understanding accident
occurrences.
