As the HSE reinforces its commitment to improving workplace
health and safety in the UK, we asks what part human error plays in the cause
of accidents at work. By Anne Harriss
Recent statistics released by the Health and Safety Executive (HSE) show
that 226 people were killed at work in 2002/03. Although this is an improvement
on previous years, Bill Callaghan, chairman of the Health and Safety Commission
(HSC), stated: "It represents continuing failure. Worker fatalities are a
blemish on a civilised society. They mark a failure of a basic human right – to
have our health and safety protected".1
Employers have a statutory duty under Section 2 of the Health and Safety at
Work. Act 1974 "to ensure as far as is reasonably practicable, the health,
safety and welfare at work of all his employees."
They must therefore have systems in place that protect their staff from
workplace accidents. Managers can only reduce the incidence of workplace
accidents if they have an understanding of the principles of accident
Accidents are unplanned, unintended events and occur as a consequence of
human error, mechanical malfunctioning, or both. Such shortfalls may have
arisen following errors in design or operation. Alternatively, they could be
the result of poor supervision or inadequate maintenance.
There is a definite link between human behaviour and accident causation.
After all, we are only human, and error is one of a number of human factors,
which affects safety performance.
This article aims to consider the part human factors and human error play in
accident causation, so that occupational health practitioners can use this
knowledge to help prevent accidents in the workplace.
An understanding of human factors in the workplace – in other words how
people function at work – is an important facet of accident prevention.
The HSE describes human factors as the perceptual, mental and physical
capabilities of people and the interactions of individuals with their job and
working environments, and the influence of equipment and system design on human
performance. It also notes characteristics of the organisation which influence
safety-related behaviour at work.2 The effective management of human factors is
therefore essential in risk management.
Lord Cullen acknowledged the significance of human factors in his report for
the HSC, which followed the Ladbroke Grove Rail enquiry. This disaster, which
resulted in multiple fatalities, occurred when a ‘signal was passed at danger’
(SPAD). Such signals are put in place to protect the public as they alert train
drivers of danger. The question must be asked why some drivers have passed
these signals, and put themselves and their passengers at risk. Has this
occurred due to the driver’s recklessness, or could there be some other reason?
Cullen comments that signals are passed at danger due to "the
limitations of human ability not adequately [being] taken into account [in work
This is a sad indictment of our railway system. It appears that one of the
causes of SPADs is a failure to see or adequately interpret track signals.
Cullen emphasises the need for train drivers to have a clear view of all the
relevant signals with the information from those signals presented in a way
that enables drivers to understand the message they are giving. In short:
"signals require to be not only visible but also readable".3 There
can be no excuse for poor design.
The Ladbroke Grove crash occurred just 18 months after another serious
accident at Southall. Cullen refers to the recommendations following the
Southall rail crash that "all parties in the rail industry… support
reliable research into human behaviour studies relating to driver
He suggests a number of factors that could have a bearing on whether a train
driver passed a signal at danger, which include the standard of driver training
and skill. However, the physical environment, signal positioning and clarity,
and the driver’s visual ability also play an important role. Cullen refers to
these as the railway’s "human-machine system". Each of these elements
plays an important part within OH practice as well.
If organisations are to be successful in accident prevention, it is
important that they are able to identify the link between the mistakes people
make, an appreciation of human factors and the accidents that result.
Accidents appear to be caused by a complex interplay of human factors and
political and economic influences. Hale proposes that health and safety
preservation is a basic goal of ‘normal’ staff, but interestingly, some do not
appear to perceive the risk to their safety. If the risk to safety is small and
the gains are great, then workers may trade off a slight increase in risk to
their safety against a larger short-term goal. Perhaps such people are
inherently risk-takers, with obvious implications for health and safety in the
The influence of the organisation in both the causation and the prevention
of accidents is of paramount importance, but often disregarded. The finger of
blame is frequently pointed at the individual who is considered to be the
‘miscreant’. This approach is misguided; if the cause of the accident is not
considered in the light of the complexity of all the possible influences, there
will always be a shortfall in safety management and accidents will be a
recurring feature within the organisation.
Safety management systems
The Cullen report makes interesting, if harrowing, reading. Reference is
made to the "short-sightedness" in blaming workers directly involved
in operational or maintenance work, while ignoring the fundamental failures
within an organisation’s management and decision-making functions.
A safety management system must acknowledge the part played by human
behaviour in risk management. Safety objectives must be set and there must be
effective communication at both individual and organisational levels. Total
commitment from management at all levels is essential, and
‘safety-consciousness’ must become enmeshed within the culture of the
organisation. Safety management systems must incorporate evidence-based
practice, and this includes an appreciation of human behaviour.
The behaviour model of Hale and Hale, developed in 1987 and cited by Boyle,
proposes that people function within a ‘systems’ model.4
Hale and Hale proposed that accidents happen when people fail to deal
appropriately with a situation presented to them. This incorporates the
individual working within the working environment and includes the concept of
information input and processing, ending with an output. Information is
constantly presented to the person who then acts on it. The elements of the
system include the method by which information is presented, and how it is
information is then perceived and processed by the worker before they take
action. The throughput can be affected by a number of factors, including
attributes of the individual, the climate of the organisation and working
conditions. The failure may be the fault of the person, the situation (which
could include a faulty plant) or both.
Unfortunately, safe working practices depend heavily on worker behaviour,
which, by its very nature, is inconsistent.
Behaviour is influenced by a number of physical and psychological factors
including the worker’s personality, knowledge and previous experience.
Performance can be adversely affected by stress, illness, medication and
fatigue, not to mention the general working environment. Poor performance may
be exacerbated by poorly designed equipment, and safety can be further
compromised by poor standards of hazard control. It is not difficult to see how
a noisy, poorly-lit working environment may contribute to the making of
Domino theories of accident causation
There are a number of domino theories, but their premise is that errors
occur within the context of the organisation.4
Heinrich suggests there is a sequence of events leading up to an accident.5
He proposes this sequence is set up rather like a line of upstanding dominoes,
so that as each one falls it triggers a chain reaction as follows:
i) The ancestry and social environment (character traits and attitudes),
ii) the fault of a person constituting the proximate reason for
iii) the unsafe act or hazard which results in
iv) the accident, which leads to
v) the injury.
Heinrich suggests that accident prevention should aim to eliminate the
unsafe act/hazard represented by the middle (third) domino so that the chain
can be broken.
This theory can be criticised as it assumes an accident results in injury
and it does not allow for the influence of management in accident prevention.
Bird and Loftus propose a more superior model as they note the important
influence of management:
i) Lack of control by management permits
ii) basic causes (personal and job factors) which lead to
iii) immediate causes (including substandard practices/conditions/errors)
which are the proximate causes of
iv) the accident, which result in
v) the loss (minor, serious or catastrophic).5
Accidents and human error
The part management plays in accident prevention is paramount, because not
only does it set the budget, specify and maintain plant and devise safe systems
of work, but it is also responsible for the recruitment, training and
supervision of human resources. And an important element of successful health
and safety management includes addressing the human factors – because accidents
often result from uncorrected errors.
For example, in the case of railway accidents, signalling errors are the
most frequent cause of train accidents. Signal-related mistakes include
failures to confirm or detect a signal, and errors in perceiving or
interpreting the signal correctly.
Since the Ladbroke Grove accident, the HSE has produced monthly
publicly-available reports on the incidence of SPADS, displayed on its website.
The total number of serious SPADs in 2002/03 was 144, a 15 per cent improvement
on the previous year and a 26 per cent improvement on the six-year average.6
Although this is a heartening improvement, it is still 144 incidents too many.
The Ladbroke Grove accident was a serious incident resulting in loss of life
and serious injuries, but a multitude of less dramatic accidents occur on a
daily basis. To attempt to reduce the incidence of errors in the workplace, it
is important to appreciate what underpins them. Stranks refers to the three
basic categories of errors:
Skill-based errors: these occur while carrying out fairly routine tasks and
result in slips, lapses and periods of inattention. They occur among highly-skilled
people and often seem to be a case of familiarity breeding contempt.
Rule-based errors: these occur when there is a set procedure, which should
be followed with a set of rules used. A rule-based error either occurs when an
inappropriate rule is made, or the worker applies the rule incorrectly.
Knowledge-based errors: these occur when a new problem has to be solved by
going back to first principles. Mistakes occur as part of an ineffective
The consideration of the capabilities of workers and their potential for
error are important factors when selecting people to undertake tasks. However,
this is only one side of the coin.
Accidents may also occur as a result of one or more of the following
– Poor job design, leading to an unsafe system of work
– Poorly-designed equipment
– Equipment that malfunctions following inadequate maintenance
– Inconsistencies in human behaviour.
Reason notes that errors may not be immediately obvious and may lie dormant
for a period of time – only becoming apparent when they combine with other
factors to cause a system failure.8 He equates these to ‘pathogens’, which are
rather like micro-organisms in the human body, which only take over to cause a
disease process when other conditions permit them do so.
Organisational safety culture
An otherwise safe system of work may become unsafe for reasons other than
error. For example, a worker may deliberately take short cuts and not follow
the safe systems of work put in place. Some may tend to take the path of least
resistance – particularly if violations go unpunished. If a safety procedure
appears trivial and is rarely sanctioned, workers may be tempted not to follow
safety guidelines. The 1986 Chernobyl nuclear disaster is one example, as the
operating circumstances resulted in deviations from what was until then a
prescribed safe system of work.
Several human factors played their part in the disaster some 20 years ago,
which had far-reaching effects across Europe. The Chernobyl reactor was
uranium-fuelled and water-cooled. The explosion occurred when an experiment was
undertaken that required the deliberate removal of layers of protection that
were designed into the system.
Ironically, the experiment’s purpose was to improve levels of safety by
ensuring a constant supply of water to cool the reactor’s uranium fuel rods.
The experiment, which was designed to avoid overheating, actually caused
overheating to occur.9
Operating the reactor under unsafe conditions led to serious instabilities
within the system. There were intrinsic fundamental design flaws, managerial
failures and transgressions of operational rules intended to prevent this type
of overheating from happening.
Glendon and McKenna note that the Chernobyl operators were highly-regarded
technicians, and the scientists were electrical engineers.10
Those running the experiment wished to solve a technical problem, with the
operators’ aim being to complete the test as quickly as possible. They
approached the experiment with the attitude that the test would be
straightforward and they would be able to run it with a ‘process feel’, rather
than following the theoretical principles of nuclear physics. It is surprising
that the report of the disaster produced by the Russian authorities identified
that the engineer in charge knew very little about nuclear reactors.
It appears that the reactor operators and engineers assumed that the other
group knew best, but neither demonstrated an appreciation of the possible
dangers. Adverse outcomes did not appear to be considered – operator actions
suggest that they believed their tests were being conducted in a safe manner.
It is likely that anyone with doubts failed to voice them, and instead were
prepared to ‘go with the flow’.
This accident clearly demonstrates a combination of latent errors within the
system, exacerbated by rule-based errors as outlined above. The organisational
culture did not appear to discourage risk-taking where there were other more
On this occasion, safety did not have a high enough priority. The HSE
identifies that the operators failed to distinguish between small and large
risks, with devastating consequences for human life and the environment.2
This clearly identifies the implications of an ineffective organisational
safety culture with scant regard for the importance of human factors. In
addition, there were flaws in the plant design and poor systems of work.
To reduce the likelihood of a disaster like Chernobyl, it is important that
sources of foreseeable error are designed out of the equipment and
work-processes. Plant and systems of work should be ‘fail-safe’ – for example,
become inoperable if operated under unsafe conditions. In the case of
Chernobyl, when the system failed it caused danger rather than failsafe devices
kicking in, with fatal consequences.
If accidents are to be prevented, a commitment to health and safety must be
embedded within the organisational culture. This can only occur if a positive
attitude to health and safety permeates down through each management layer from
the very top of the management structure. Management’s insistence on safety
must be continuously visible. Safety will deteriorate if procedures and safe
systems of work are lax, and workers are discouraged from working to safety
standards by production targets. If management takes no action to enforce
safety, workers will fail to change their behaviour because unsafe practices
appear to be acceptable to the organisation.
This article demonstrates that accident causation is inextricably linked to
human factors and human error, operating in the context of the organisation.
To fulfil its responsibility to ensure a safe working environment,
management must make safety a high priority. A safety management system is the
means by which the organisation controls risk through the management process.
It would be na‹ve to suggest that all accidents could be prevented. Managers
should instead reflect on how errors could be reduced. They must be able to
apply an understanding of human factors, be prepared to select appropriate
staff, safe equipment, and devise safe systems of work. They may also of course
seek assistance from OH practitioners in order to do this effectively.
Anne Harriss is the OH course director at London South Bank University
1. HSE (2003) www.hse.gov.uk/press/2003/ c03038.htm
2. HSE (1989) Human Factors In Industrial Safety London: HMSO
3. Health and Safety Commission ( 2001) The Ladbroke Grove Rail Inquiry –
Part 1 Report, Suffolk: HSE Books
4. Boyle, T (2000) Health and Safety Risk Management, Leicestershire: IOSH
5. Stranks, J (1994) Human Factors and Safety, London: Pitman Publishing
6. HSE (2003) www.hse.gov.uk/railways/spads.htm
7. Stranks, J (1994) Human Factors and Safety, London: Pitman Publishing
8. Reason, J (1990) Human Error, Cambridge University Press
9. Haynes, . Bojcun, M (1988) The Chernobyl Disaster, London: Hogarth Press
10. Glendon, I, McKenna, E (1995) Human Safety and Risk Management, London:
Chapman and Hall