Human error
A human error (hereinafter, the Error) is any unintentional action or inaction of a human being working on a system that can potentially degrade this system. In other words, the Error can be defined as an individual's deviation from acceptable or desirable practice which culminates in undesirable or unexpected results.
Those actions or inactions that can potentially degrade the system that shouldn't be degraded and are made intentionally, on the purpose to do so, are called violations. Together, the residual Errors and violations are known as unsafe behaviors.
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Classification
Dr. Jens Rasmussen developed a scientific classification of the Errors. This classification claims that a human being is making the Error while performing either:
- An incorrect task. This type of the Error has been categorized as a mistake, which J. Rasmussen further classified as either a rule-based or knowledge-based; OR
- A correct task incorrectly. Commonly, this type of the Error is categorized as a slip or lapse.
Mistakes
- Main wikipage: Planning mistake
Slips
- Main wikipage: Slip error
Lapses
- Main wikipage: Memory lapse
Other groupings
Similarly to human performance, the Errors can be grouped in many ways.
Well-adjusted vs residual
Dirty Dozen
- Main wikipage: Human Factors Dirty Dozen
- Originally developed by Transport Canada, Human Factors Dirty Dozen is a highly popular grouping of the Errors that is used in aviation.
Unsafe behaviors
- Main wikipage: Unsafe behavior
- J.T. Reason, as expressed in the CAA Flight-crew human factors handbook CAP737, developed the classification of unsafe acts that distinguishes between two types of the Errors':
- Active failures, whose effects are felt immediately in a system. Active failures are usually the result of actions taken (or not taken) by front-line operators such as pilots, air traffic controllers, or anyone else with direct access to the dynamics of a system.
- Latent failures, whose effects may lie dormant until triggered later, usually by other mitigating factors. Latent failures, on the other hand, are caused by those separated by time and space from the consequences of their actions in the dynamics of the system. Personnel working in vocations such as architectural design, hardware design and equipment maintenance are more prone to cause latent failures than active failures. On another hand, consider the case of a mechanic who assembled a component incorrectly which eventually led to a plane crash days or even weeks later. The defenses that should have normally caught this mistake were not in place. These defenses include proper training (the mechanic was taught to fix this particular component very informally and on-the-job), good situational awareness (the mechanic was tired from a double shift the night before), and independent inspection (the job was "pencil-whipped" to save time).
Consequences
- Main wikipage: 300-29-1 Theory
- An unsafe act can be defined as the Error that hasn't been corrected timely within the same set of enterprise efforts. Further, unsafe acts may lead to incidents, and those may cause accidents, including fatal accidents. One proportion for those unsafe acts that led to the catastrophes is known as the 300-29-1 Theory:
Type Description Number Unsafe act Those Errors that haven't been corrected properly 300 Incidents Those unsafe events that lead to minor failures 29 Accidents Those incidents that lead to fatal accidents or catastrophes 1
Prevention
The Error is one of the many contributing causes of risk events and a significant cause of disasters and accidents in industries such as nuclear power, aviation, space exploration, and medicine. Prevention of the Errors and/or their impact is a major contributor to reliability and safety of complex systems. Studies of human factors and ergonomics that allow for reduction of the Errors are the focus of several disciplines such as crew resource management (CRM) and maintenance resource management (MRM).
