The nice thing about being a psychologist is that you can sit in your ivory tower and not be forced to quantify human errors. Unfortunately, that is ultimately what HRA is all about.

—E. M. Dougherty, Jr. (1990)


Humans are involved in all life phases of most technical systems, from design through construction, operation, management, maintenance, and system upgrade, to decommissioning/disposal. Humans tend to make errors and it is often said that “to err is human.” As humans, we are generally more complex than technical systems and it is therefore difficult to predict the types of errors that we may commit.

A feature that makes us very different from technological systems is our ability to detect and recover our own errors as well as errors committed by other persons or by technical systems. Bearing this in mind, we may claim that human actions contribute significantly to risk—but also to safety.

Knut Øien, SINTEF/NTNU, has made important contributions to this chapter.

Human errors are often claimed to account for somewhere between 60% and 90% of all accidents in industry and transport. Such a statement may be counterproductive. Since humans are involved in all phases of a system's life cycle, almost all accidents can be traced back to some kind of human error or inadequate decisions in an earlier phase. This view is supported by the following quotation:

Since no system has ever built itself, since very few systems operate ...

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