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Topic Three
Accident Aetiology
Objectives of this Section
 To outline how accidents are caused;
 To demonstrate the role of human error in
accident causation.
 To outline strategies for reducing human
error.
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The Domino Theory
Accident sequence was likened to a row of dominoes
knocking each other down.
The accident is avoided by removing one of the
dominoes, normally the middle one or unsafe act.
ILCI Model
This update introduced two new concepts;
 The influence of management and managerial error;
 Loss, as the result of an accident could be production
losses, property damage as well as injuries.
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Multi-causation
Behind every accident there lies many contributing
factors, causes and sub-causes.
IMMEDIAT
ROOT
BASIC
E CAUSE
CAUSE
CAUSE
(Lack
of
Control)
 cause a   cause d   cause f
 cause b
 cause e
 cause c


INCIDENT
LOSS


Conclusion
 All accidents whether major or minor are caused,
there is no such thing as an accidental accident!!
 Very few accidents, particularly in large organisations
and complex technologies are associated with a
single cause.
 The causes of accidents are usually complex and
interactive.
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The Role of Human Error in
Accidents
“The actions of people account for 96% of all
injuries” – (DuPont)
“80-90% of accidents are due to human error”
(Heinrich et al, 1980)
“50-90% of accidents according to statistics are
due to human failings” – Kletz (1990)
“We seem to have passed the era where the
need was for further engineering safety
guards….What we have to do is to capture the
Human Factor”
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In recent years the UK has suffered a large number of
tragic disasters. These include:
 Kings Cross Underground Fire
(1987)
31 people killed
 Capsize of the Herald of Free
Enterprise Ferry (1987)
189 people killed
 Clapham
(1988)
crash
35 people killed and
500 injured.
 Piper Alpha Oil Rig Explosion
(1988)
167 people killed
Junction
rail
Two common points arose from the inquiries:
 The influence of human error in the chain of events
leading to the accident;
 Failures in the management and organisation of
safety.
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The Traditional Concept of Human
Error
 Look for the immediate cause – an unsafe act
 Blame the individual concerned.
The Blame approach - Options
 You accept that human error is inevitable, shrug your
shoulders, tell him to be a bit more careful and carry
on as before with your fingers crossed.
 Alternatively, you can say as he was responsible, you
should discipline him, perhaps even sack him.
 Give him the benefit of the doubt and retrain the man
(You will almost certainly therefore be reduced to
repeating the training which you know has already
failed!).
__________________________________
 This is the approach that has existed in most
organisations for years.
 It is no use whatsoever to blame people for their
mistakes unless we have a detailed understanding of
what caused the mistakes.
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Organisational & Managerial
Failures
Lessons from recent disasters
Inquiry into the King’s Cross
Underground Station Fire
Many of the shortcomings in the physical
and human state of affairs at King’s Cross
on 18 November 1987 had in fact been
identified before by internal inquiries into
escalator fires.....The many
recommendations had not been adequately
considered by senior managers...London
Underground’s failure to carry through the
proposals resulting from earlier fires......was
a failure which I believe contributed to the
disaster at King’s Cross.
I have said unequivocally that we do not
see what happened on the night of 18
November 1987 as being the fault of those
in humble places.
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Attitudes to Safety
Inquiry into the King’s Cross
Underground Station Fire
Although I accept that London Underground
believed that safety was enshrined in the
ethos of railway operation, it became clear
that they had a blind spot....
I believe this arose because no one person
was charged with overall responsibility for
safety. Each director believed he was
responsible for safety in his division, but
that it covered principally the safety of staff.
The operations director, who was
responsible for the safe operation of the
system, did not believe he was responsible
for the safety of lifts and escalators which
came within the engineering director’s
department. Specialist safety staff were
mainly in junior positions and concerned
solely with safety of staff.
Inquiry into the capsize of the Herald of
Free Enterprise
Do they need an indicator light to tell them
whether the deck storekeeper is awake and
sober? My goodness!!
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Inquiry into the Clapham Junction Rail
Crash
All concerned in management, from the
members of the Board of Directors down to
the junior superintendents, were guilty of
fault in that all must be regarded as sharing
responsibility for the failure of management.
From the top to the bottom the body
corporate was infected with the disease of
sloppiness.
The direct cause of the Clapham Junction
accident was undoubtedly the wiring errors
made by Mr. Hemmingway in his work in
the Junction “A” relay room.
Later, the report goes on to state...
The concept of absolute safety must be a
gospel spread across the whole workforce
and paramount in the minds of
management. The vital importance of this
concept .. was acknowledged time and
again in the evidence which the Court
heard ...
But, subsequently it also states…
The concern for safety was permitted to coexist with working practices which ... were
positively dangerous ... The best of
intentions regarding safe working practices
was permitted to go hand in hand with the
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worst of inaction in ensuring that such
practices were put into effect.
Inquiry into the Piper Alpha Oil Rig Fire
I am convinced from the evidence ... that
the quality of safety management .... is
fundamental to off-shore safety. No amount
of detailed regulations for safety
improvements could make up for
deficiencies in the way that safety is
managed.
General conclusions which can be drawn from the
above disasters:
 Not one of these organisations had, before the
accidents, any serious reservations about their safety
procedures, organisation or management, yet there
were clearly many problems of which they were not
aware.
 Errors made “at the sharp-end” must be seen in the
wider context of the organisation and management
climate in which they were committed.
 Actions speak louder than words. The best of written
safety policies, the most detailed set of safety rules
and procedures etc. are totally meaningless unless
they are fully resourced, rigorously implemented and
kept under regular review.
 Commitment, positive safety attitudes and motivation
together with constant vigilance throughout the
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organisation (but led from the top), are essential to
high safety standards.
 You cannot rely on external prescription to achieve
safety.
Classification of Human Error
Active/Latent Failures
Active Failures
 Have an immediate consequence
 Are usually made by front-line people such as drivers,
control room and machine operators.
 Immediately precede, and are the direct cause, of the
accident.
Latent Failures
 Those aspects of the organisation
immediately predispose active failures.
which can
 Common examples of latent failures include:
 Poor design of plant and equipment.
 Ineffective training.
 Inadequate supervision.
 Ineffective communication.
 Uncertainties in roles and responsibilities.
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Latent failures are important to accident prevention
because
1. If they are not resolved, the probability of repeat
accidents remains high regardless of what other
action is taken.
2. As one latent failure often influences several potential
errors, removing latent failures can be a very costeffective route to accident prevention.
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Classifying Active Failures (1)
Human Failures
Violations
Human Errors
Routine
Mistakes
Skill-based errors
Situational
Rule-based
Slips of action
Exceptional
Knowledge-based
Lapses of memory
Slips and Lapses:
Occur in routine tasks with operators who know the
process well and are experienced in their work:
 Action errors which occur whilst the task is being
carried out.
 Often involved missing a step out of a sequence or
getting steps in the wrong order and frequently arise
from a lapse of attention.
 Typical examples: Operating the wrong control
through a lapse in attention or accidentally selecting
the wrong gear.
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Classifying Active Failures (2)
Human Failures
Violations
Human Errors
Routine
Mistakes
Skill-based errors
Situational
Rule-based
Slips of action
Exceptional
Knowledge-based
Lapses of memory
Mistakes:
 Inadvertent errors that occur when the elements of a
task are being considered by the operator.
 Decisions that are subsequently found to be wrong,
although at the time the operator would have believed
them to be correct.
Violations
 Deliberate deviations from the rules which are
deemed necessary for the safe operation of
equipment.
 Breaches in these rules could be accidental or
deliberate.
 Violations are seldom wilful acts of sabotage or
vandalism.
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Latent Failures
King’s Cross Underground Station Fire
The latent failures here included:
1. While several minor escalator fires had occurred
previously and had been investigated, apparently no
one in the organisation seriously considered the fact
that a major escalator fire was a possibility consequently, as the inquiry states, little effective
action had been taken on the warnings provided by
the minor fires.
2. Similarly the inquiry also reported that there were
serious flaws in the managerial and organisational
responsibilities and accountability for safety with
virtually all aspects of the organisation thinking
passenger safety was someone else’s responsibility.
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Latent Failures
The Capsize of the Herald of Free
Enterprise
Among the latent failures involved here are the
following:
1. It was impossible for anyone to on the bridge to see
whether the bow doors had been closed prior to
setting sail.
Although there were organisational procedures in
place the Officer in charge was, effectively, working
on the basis of “faith” rather than any more positive
feedback of information.
2. This design latent failure was compounded by the
attitude of the senior management in the memos in
reply to a request for an on-bridge warning device.
For a formal request concerning a major safety issue,
from a senior operational manager, to be treated in
such a way clearly indicates that there was apparently
very little credibility given to potential safety issues.
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Latent Failures
Attitudes to Safety:
A safety culture depends on the attitudes to safety
shown by management and supervisors.
Rules & Procedures:
Studies have shown that safety rules and procedures
are often:
 Written negatively, concentrating on should not be
done rather than on what should be done.
 Impractical.
 In conflict with other rules.
Training:
 Little consideration is
effectiveness of training.
given
to
evaluating
the
 Hazard awareness is often assumed rather than
trained.
 Training should concentrate on what is safe, rather
than unsafe, what to do, rather than what not to do.
 Training is not always consistent with the rules and
procedures.
Equipment design & Maintenance:
 limitations in the standard of ergonomics applied to
the design of the equipment/plant increase the risk of
human error.
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Strategies for Reducing Human
Error
Reducing human error involves far more than taking
disciplinary action against an individual.
Actions for overcoming Active
Failures
Slips and Lapses
Design improvement is the most effective route for
eliminating the cause of this type of human error.
Typical problems:
 Switches which are too close and can be inadvertently
switched on or off.
 Displays which force the user to bend or stretch to
read them properly.
 Critical displays not in the operators field of view.
 Poorly designed gauges.
 Displays which are cluttered with non-essential
information and are difficult to read.
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Mistakes
 Training is the most effective way for reducing mistake
type human errors.
 Based on defined training needs and objectives.
 Evaluated to see if it has
improvement in performance.
had
the
desired
Violations
There is no single best avenue for reducing the potential
for deliberate deviations from procedures.
Consider the factors that reduce an individuals
motivation to violate which include:
 Under-estimation of the risk.
 Real or perceived pressure from the boss t adopt poor
work practices.
 Pressure from work-mates to adopt their poor working
practices.
 Cutting corners to save time and effort.
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Addressing Latent Failures
The organisation must create an environment which:
 Reduces the benefit to an individual from violating
rules.
 Reduces the risk of an operator making slips/lapses
and mistakes.
This can be done by identifying and addressing latent
failures.
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