Human Factors vs Accident Causation

Accidents are caused by active failures or and latent conditions which can lead to human error or violations. Active failures are the acts or conditions precipitating the incident situation. They usually involve the front-line staff, the consequences are immediate and can often be prevented by design, training or operating systems.

Latent conditions are the managerial influences and social pressures that make up the culture ('the way we do things around here'), influence the design of equipment or systems, and define supervisory inadequacies. They tend to be hidden until triggered by an event. Latent conditions can lead to latent failures: human error or violations. Latent failures may occur when several latent conditions combine in an unforeseen way. We all make errors irrespective of how much training and experience we possess or how motivated we are to do it right. Considering the active failures and latent conditions in an organisation the model of accident where human error is main cause of accident can be shown in figure below.

People can cause or contribute to accidents (or mitigate the consequences) in a number of ways:

  • Though a failure of a person can directly cause an accident. However, people tend not to make errors deliberately. We are often 'set up to fail' by the way our brain processes information, by our training, through the design of equipment and procedures and even through the culture of the organisation we work for.
  • People can make disastrous decisions even when they are aware of the risks. We can also misinterpret a situation and act inappropriately as a result.Both of these can lead to the escalation of an incident.
  • On the other hand we can intervene to stop potential accidents. Many companies have their own anecdotes about recovery from a potential incident through the timely actions of individuals. Mitigation of the possible effects of an incident can result from human resourcefulness and ingenuity.
  • The degree of loss of life can be reduced by the emergency response of operators and their colleagues in a team. Emergency planning and response including appropriate training can significantly improve rescue situations.

The consequences of human failures can be immediate or delayed and the failures can be grouped in to the following categories:

Active failures have an immediate consequence and are usually made by front-line people such as drivers, control room staff or machine operators. In a situation where there is no room for error these active failures have an immediate impact on health and safety.

Latent failures are made by people whose tasks are removed in time and space from operational activities, e.g. designers, decision makers and managers. Latent failures are typically failures in health and safety management systems (design, implementation or monitoring).

Examples of latent failures are:

  • Poor design of plant and equipment;
  • Ineffective training;
  • Inadequate supervision;
  • Ineffective communications;
  • Inadequate resources (e.g. people and equipment); and
  • Uncertainties in roles and responsibilities
  • Poor SOPs.

Latent failures provide great, if not a greater, potential danger to health and safety as active failures. Latent failures are usually hidden within an organisation until they are triggered by an event likely to have serious consequences.

After an accident involving human failure the investigation into the causes and contributing factors often makes little attempt to understand why the human failures occurred. Finding out both the immediate and the underlying causes of an accident is the key in preventing similar accidents through the design of effective control measures.


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