Human error is behavior that is wholly expected to achieve a desired result (in accordance with some standard) but that does not. A causal factor is anything that yields an occurrence resulting in an undesired effect or anything that exacerbates the level of severity of the undesired effect.

Why is it important to understand human error causal factors? The answer is twofold.

First, a good design (either the design of a process or hardware item) is created, in large part, with an understanding of:

1. Any potential undesired effects in operating or maintaining the process or in manufacturing, transporting, storing or using the hardware item
2. The human errors and their causal factors that can activate these undesired effects.

With this understanding, the intent is to design such as to eliminate the potential for the undesired effects, or when that can’t be done, to establish appropriate barriers for the:

1. Prevention of any error that could activate the undesired effect
2. Timely detection of the error
3. Mitigation of the undesired effect.

Of course, the resources applied to any such barriers are appropriate to the level of significance of the undesired effect.

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