Hazard Analysis

Hazard analysis is the systematic identification of sources of potential harm in a system, process, or environment. It is the first phase of risk assessment, preceding the estimation of probabilities and the evaluation of consequences. The method demands imagination: the analyst must conceive of failure modes that have not yet occurred, operating at the boundary between known risks and unknown unknowns.

The most rigorous form is the HAZOP study, developed in the chemical industry, which applies a structured set of guide words (more, less, as well as, reverse, etc.) to every process parameter to discover deviations from design intent. The strength of hazard analysis is its procedural discipline; its weakness is that it is only as good as the analyst's ability to imagine the unimaginable. The Therac-25 accidents were not caused by a hazard that had been analyzed and dismissed, but by a hazard — the software race condition — that had not been conceived of at all.