Health and Safety
Executive
Human Factors
in Accident
Investigation
David Birkbeck
HID Onshore Human &
Organisational Factors Group
Health
Healthand
andSafety
Safety
Executive
Executive
Human Factors
in Accident
Investigation
David Birkbeck
HID Onshore Human &
Organisational Factors Group
Introduction
•
‘To say accidents are due to human failing
is like saying falls are due to gravity. It is
true but it does not help us prevent them’
Trevor Kletz
•
Aim today is to present methods that are
known to help identify human failure in
accident investigation and prevent
reoccurrence
•
Not a black art, a pragmatic and robust
process
What we expect
•
Methodical process for
gathering information,
analysing what went
wrong (and right), and
learning lessons in order
to:
– Manage risk
– Prevent reoccurrence
•
Retrospective tool, but
can be powerful in
promoting change
Accident reports
•
•
•
•
•
What happened
Who to
When
How it happened
But not why
Technical myopia
Failure to consider human factors
Significance of human factors
•
Up to 90% of accidents attributable to
some degree to human failures
•
...Texas City…Buncefield... …Texaco
Milford Haven ... Southall and Ladbroke
Grove crashes ...Zeebruger…
•
Proportion and significance increasing as
technical safety measures improve
Recent news
But not as simple as we think..
•
‘This accident was the result of human
error’
– ‘…..pilot error’
•
Error or rule-breaking put down to
– ‘Lack of competence’
– ‘Poor supervision’
– ‘Not paying attention’
•
It’s not usually as simple as that!
Human failure taxonomy
Human failures
Intended actions
Unintended actions
Violation - Intended consequences
When the person decided to act without complying with a known
rule or procedure
Errors - Unintended consequences
Mistakes
When the person does
what they meant to,
but should have done
something else
Lapses
Slips
When the person
forgets to do
something
When the person does
something, but not
what they meant to do
Slip, lapse or mistake?
No
Was there prior
intention to act?
No
Was there
intention in the
action?
Yes
Yes
Did the actions
proceed as
planned?
No
Involuntary or
non-intentional
action
Spontaneous or
subsidiary action
Unintentional
action (slip or
lapse)
Yes
Did the actions
achieve their
desired end?
Yes
Successful
action
No
Intentional but
mistaken action
How to apply
•
•
•
•
Create timeline
•
Record
Identify significant behaviours
Analyse behaviours
Identify effective measures to prevent
reoccurrence
Errors
•
Slip
– When a person does something, but
not what they meant to do
•
Lapse
– When a person forgets to do
something
•
Both are unintended actions with
unintended consequences
Example slip – Emirates EK407
•
•
Emirates Flight EK407
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This weight was entered into take off
performance software on separate laptop
•
Captain noticed something was wrong at
the end of the runway, took manual
control and selected maximum thrust
Pre-flight take off calculations were based
on an incorrect take off weight (262M/t
rather than 362M/t)
Example slip – Emirates EK407
Example slip – Emirates EK407
•
After the accident, Captain and First Office were
asked to resign by Emirates and did so
•
ATSB investigation revealed:
– Captain had flown 99 hours in last month (1
hour below maximum)
– Had slept for 3.5 hours in 24 hour period prior
to flight (shift rotas)
– Excessively complex system for calculating
take off speed (manual transfer of information
from 2 automated systems)
– No automated failsafe
Mistakes
•
When a person does something they
intended to do, but should have done
something else
•
Rule based – choosing a standard solution for a
known problem – the maintenance worker who
selects the wrong isolation procedures
•
Knowledge based – working from first principles
– 3 Mile Island shift team dismissed a potential
explanation for the unfolding incident as they
believed a valve was closed
Mistakes
•
Because the action is
intended, mistakes
are much harder to
detect at the
individual level
•
People believe what
they are doing is right
and often dismiss
evidence to the
contrary
– Bias
– Tunnel vision
Violations
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The Texas City technicians who filled the
raffinate splitter to 90-100% capacity
rather than 50% as stated in procedures
•
The Assistant Boson who was asleep
rather than checking the bow doors were
closed on the Herald of Free Enterprise
•
The technicians who knowingly
maintained the Chernobyl reactor in an
unsafe state to allow a safety study to be
conducted
Violations
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Violation
– When a person decides to act without
complying with a known rule or
procedure
•
Note that, in this context, there must be
an known rule or procedure
•
This is not a moral or ethical judgement
Violations
Violations
•
Note that we all integrate rule violation
into our day to day lives so the
identification of a violation should not be
regarded as a precursor to discipline
•
Indeed, we tend to like those who break
the rules
Violations
Violations
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Types of violations
– Routine
– Exceptional
– Acts of sabotage
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The key to the effective analysis of
violations is to understand why
– What antecedents were present?
– What behaviour was observed?
– What consequences resulted?
Performance Influencing Factors
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Defined as ‘the characteristics of the job, the
individual and the organization that influence
behaviour’
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Considered during behavioural analysis, often at
the end of the process
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Very broad topic including a range of factors e.g.
fatigue, group effects, design of equipment,
mental wellbeing, task knowledge/complexity
•
•
A comprehensive list available on HSE website
Often have a critical role in error causation but
equally often overlooked (e.g. fatigue EK407)
Performance Influencing Factors
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Can profoundly influence potential for error
(proposed nominal human unreliability). Task
is:
• Routine, highly practiced, rapid task involving
relatively low level of skill (0.02)*
• Miscellaneous task for which no description can
be found (0.03)*
• Fairly simple task performed rapidly or given
scant attention (0.09)*
• Totally unfamiliar, performed at speed with no
real idea of consequence (0.55)*
*Williams, J.C. HEART Technique
Common issues
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Failure to correctly specify behaviour
– The individual involved
– The task they were engaged in at the time
– What they did (or did not do)
– What the outcome was
•
Making early decisions and sticking to them
– As information becomes available, a mistake
can become a violation
•
Failure to identify the multiple behaviours
contributing to an accident or incident
– Timeline critical
Why bother with any of it?
•
Each failure type has a different set of solutions designed
to prevent their reoccurrence. For example (not
exhaustive):
– Slip/Lapse
• NOT training
• Hardware solutions
• Cross checks
• PIFs
– Error
• Training e.g. scenarios
• Group support
• Challenge
– Violations
• Behaviour modification
• Culture improvement
What to remember
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Human behaviour can be predicted with
reasonable accuracy
•
Correctly integrating HF into your accident
investigation process will reap rewards – just
look at the contemporary causation figures
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Separating error, mistake and violation
represents a highly valuable first step
•
Help is out there
– Guidance
– HSE
– Industry working groups e.g. Energy Institute
A final thought
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The most powerful influence on human
behaviour is outcome
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Therefore managing human failure requires a
high degree of corporate honesty:
– What behaviour is really rewarded?
– Are we willing to look at organizational
factors, especially when we see rule
breaking?
– Are we willing to make the investments that
are likely to prevent reoccurrence?
– Are we willing to strive for objectivity and
pragmatism?
Sources of guidance
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Reducing Error & Influencing Behaviour
HSG 48
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Investigating Incidents & Accidents HSG
245
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Successful Health & Safety management
HSG 65
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Human Factors Website pages
http://www.hse.gov.uk/humanfactors/majorhazard/index.htm
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Energy Institute guidance
http://www.energyinst.org.uk/index.cfm?PageID=1268