(153c) "Managing the Intolerable"

Quantitative risk assessments are used within the field of process safety to decide what is and is not appropriate. Typically risk assessments involve the evaluation of probabilistic measures that estimate the average expected value for the situation being considered across a range of potential outcomes. The resulting expected value is then used to determine if a situation represents an acceptable or unacceptable risk based on a threshold value allotted to the scenario. This approach often gives guidance that is at odds with the thoughts and behaviors of some stakeholders as illustrated by the ?but what if it does happen?? type of question. This inconsistency results from the inherent limitation associated with expected value approaches in that the methodology is based on whether or not a situation represents an acceptable risk while overlooking the possibility that a situation represents an intolerable event. This paper looks at an adjustment to traditional quantitative risk assessments so as to assess both the acceptability of risk and the tolerability of the associated consequences relative to risk criteria. These adjustments have been found to better represent stakeholder perceptions of risk, more closely relate risk tolerance to corporate values and resources, and to better justify the use of various risk transfer strategies.