For potential hazards identified, both the severity of consequences and the likelihood of occurrences are considered when ranking the risk of an activity.
Subject Matter Experts (SMEs) as well as the project leader, equipment designers, workers and others involved in the project, and facilities and line management should be involved in categorizing the hazards and associated risks of the project.
Either qualitatively or quantitatively, each hazard associated with activities in the work scope is categorized as for example, negligible, low, moderate or high risk.
Both qualitative and quantitative tools are available to assist in determining the level of risk associated with the identified hazards. OSHA 1910.119 gives guidelines for "preventing or minimizing the consequences of catastrophic releases of toxic, reactive, flammable, or explosive chemicals. These releases may result in toxic, fire, or explosion hazards." The standard indicates that a hazard evaluation must be performed and "the employer shall use one or more of the following methods:"
- What-If (qualitative)
- Checklist (qualitative)
- What-If/Checklist (qualitative)
- Hazard Operability Analysis (HAZOP)(qualitative)
- Failure Modes and Effects Analysis (FMEA) (quantitative)
- Fault Tree Analysis (quantitative)
- An appropriate equivalent methodology (both)
Ordin, P.M. "A Review of Hydrogen Accidents and Incidents in NASA Operations" Proceedings of the 9th Intersociety Energy Conversion Engineering Conference, American Society of Mechanical Engineers, 1974. (pdf, )