ABSTRACT
In the history of system safety, the human factor has been considered in three quite different roles. In the first role, the human factor was looked at as a bottleneck and as something that hindered the full use of the technological potential. In the second role, the human factor was looked at as a liability or a threat, and humans were seen as something that limited performance as well as being a source of risk and failure. In the third role, the human factor is looked at as an asset, and humans are seen as a sine qua non for system safety.
