Identification of Scenario Candidates for Hazard Evaluation

The identification of potential scenarios or hazardous situations in performing Hazard Evaluation can be a challenging and very time consuming activity. These scenarios focus on the potential causes and outcomes of episodic events (such as explosions or major toxic releases) rather than the potential effects of conditions that may routinely exist in the workplace (such as hazards associated with elevated work or routine line and equipment opening). A modified Hazard and Operability Analysis (HAZOP) technique is an effective means for an analysis teams to quickly develop a list of scenarios for consideration that ensures consistency and thoroughness of the Hazard Evaluation among evaluation teams.

Starting with a feasible incident (such as activation of a relief device, catastrophic failure of equipment or loss of containment) for a specific item of equipment, the potential causes and outcome may be determined. HAZOP “parameters” associated with control of the process such as temperature, pressure and flowrate; and “deviations” from the design intent such as high pressure, low temperature or no flow may be utilized in a simple Fault Tree to identify causes for hazardous situations that could lead either directly or indirectly to an incident. The feasibility of various outcomes (such as vapor cloud explosion or toxic infiltration to an occupied building) resulting from the incident may be evaluated using a simple Event Tree to complete the initial description of a hazard scenario.