Hazard analysis identifies possible hazard scenarios for a process or facility (CCPS, 1992). Qualitative risk estimates are often included in hazard analysis. OSHA's Process Safety Management (PSM) standard, 29 CFR 1910.119 and EPA's Risk Management Program (RMP) rule, 40 CFR Part 68, require that a process hazard analysis (PHA) be performed for processes covered by the regulations and that, among other things, "the PHA shall address human factors."
Hazard analysis must address human failures together with equipment failures and external events as possible causes of hazard scenarios (see Figure 26-1). Note that equipment failures may be attributed ultimately to human failures on the part of process designers, specification engineers, fabricators, maintenance personnel, etc. and some external events are also human induced. Human failures may be initiating events, intermediate events, or enabling events for hazard scenarios. Closing the wrong valve may be an initiating event, failure to respond to an alarm may be an intermediate event, and bypassing a trip may be an enabling event.
Hazard analysis should also address the human factors that influence the likelihood of human failures occurring. For example, an operator may fail to close a manual valve in a line when required to do so. This could be the initiating event for a hazard scenario. The human factors that influence the likelihood of this failure must be identified in order to 1) assess the likelihood of the failure, 2) identify existing safeguards that may protect against it, and 3) decide what recommendations may be needed to reduce the risk to a tolerable level. For example, the valve may not be labeled, it may be located close to another similar valve in an adjacent line, operator training or procedures may be inadequate, etc.
Treatment of human factors in hazard analysis requires:
ศ Identification of human failures as causes of or contributors to hazard scenarios. ศ Identification of human factors that influence the likelihood of human failures. ศ Optionally, qualitative assessment of the likelihood of human failures.