No doubt, humans add value to an organization. They provide creativity and expertise to the process and ideas for improvement. They are flexible, can adapt to changes, and perform tasks that machines are not capable of yet. But humans are also the Achilles heel in reliability vulnerabilities. American writer and humorist Kurt Vonnegut wrote, “If it weren't for the people always getting tangled up with the machinery... Earth would be an engineer's paradise.”
U.S. Department of Defense (DoD) statistics suggest that human error is a causal factor in 80-90% of all mishaps. In John Moubray’s RCMII book, more than 70% of equipment failures are self-induced, with 40% coming from human error. Winston Ledet’s work at DuPont suggests that 84% of failures are due to careless work habits. If these numbers are so high, shouldn’t we do something about it?
To explain the categories of human error, we can consider two models. The DoD’s Human Factors Analysis and Classification System (HFACS 8.0, April 2023) uses the same groupings presented by James Reason in his model: organizational influences, unsafe supervision, unsafe acts, and preconditions for unsafe acts. Secondly, Benjamin Blanchard, Dinesh Verma, and Elmer Peterson’s book Maintainability grouped the main factors impacting the interaction between people and machines under four headings. These are anthropometric, human sensory, physiological, and psychological factors.
External factors
Anthropometric factors refer to the physical characteristics of the human body that can affect performance and contribute to human error. These factors can include body size, shape, and strength. Errors occur because the hand or arm cannot fit in the space or the individual is not strong enough to lift or move an item. One example of anthropometric factors contributing to human error is when a worker cannot reach a control panel or button because it is too high or too low for their height. This can cause the worker to strain or stretch to reach the controls, increasing the likelihood of mistakes and reducing overall efficiency.
With human sensory factors, when working with machinery, a worker can be affected by poor lighting or noise levels, making it difficult to see or hear important cues or signals. For example, a worker may misinterpret a warning signal or overlook a malfunctioning component, leading to errors or accidents.
Physiological factors can contribute to human error in equipment reliability. These factors include physical and mental fatigue, stress, and illness. Physical and mental fatigue can impair a worker's ability to perform tasks safely and efficiently. When workers are fatigued, their reaction time may be slowed, and their decision-making abilities may be impaired, increasing the likelihood of errors. For example, a fatigued worker may be more likely to overlook a critical step in a procedure or make a mistake when handling machinery.
The three categories above relate to external events, which can cause a human to make an error. They are easy to address but may require considerable expense to do so. The last grouping of psychological factors is more complex and challenging.
Psychological factors
Within psychological factors, we can classify errors as unintended or intended. “Unintended” errors can be split into two categories, slips and lapses. These are skill-based errors. Mistakes occur when someone does things incorrectly, even though they may have done it correctly many times before. Lapses occur when a technician leaves a critical step in a process or sequence. Maybe they leave a tool inside the equipment or forget to open a process valve.
“Intended” errors can be split into mistakes and violations. Within the mistakes category, there are rule-based mistakes and knowledge-based mistakes. With rule-based mistakes, the error can come from the misapplication of a good rule or applying a bad one. With knowledge-based mistakes, inappropriate responses are provided to an abnormal situation with no rules. Mistakes like these are less likely when operators and maintainers are trained in the systems and how the processes work.
Lastly, in the Intended actions category are violations. Violations can be routine violations, exceptional violations, and acts of sabotage. An example of a routine violation is not wearing hearing protection when the site requires it. Exceptional violations are when someone rushes out to the plant floor without their safety glasses because they could not find them or did not have time to look for them. Sabotage is a malicious act that creates failure.
People still overcome human error
When determining that human error is the root cause, the cause becomes the failure mode. If the failure is an inappropriate response to other failures, it is listed as a failure effect. The best way to overcome human error is to involve people. People commit errors, can identify errors, and can provide effective solutions.
