New CCPS Guideline Book: Guidelines for Conditional Modifiers and Enabling Conditions

Safety and Health Division
AIChE Spring Meeting and Global Congress on Process Safety
April 30, 2013 - 10:15am-10:45am

This paper outlines the content of a new CCPS book entitled Guidelines for Conditional Modifiers and Enabling Conditions.  A conditional modifier is one of several possible probabilities included in scenario risk calculations, generally when risk criteria endpoints are expressed in impact terms (e.g., fatalities) instead of in primary loss event (e.g., release, vessel rupture). Conditional modifiers include, but are not limited to: probability of a hazardous atmosphere, probability of ignition, probability of explosion, probability of personnel presence, probability of injury or fatality, and probability of equipment damage or other financial impact.  An enabling condition is a condition that is not a failure, error or a protection layer but makes it possible for an incident sequence to proceed to a consequence of concern. It consists of an operating phase or condition that does not directly cause the scenario, but that must be present or active in order for the scenario to proceed to a loss event; expressed as a dimensionless probability. These Guidelines for Conditional Modifiers and Enabling Conditions contain information useful to the experienced analyst and accomplished practitioner. In this book, various kinds of enabling conditions and conditional modifiers are defined and illustrated as they might be used in LOPAs.  There is a discussion on how enabling conditions and conditional modifiers can be used in other risk analysis applications. The appendices discuss “double jeopardy” and simultaneous failures, peak risk, and example rules for enabling conditions and conditional modifiers.

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