The development of risk criteria for high severity low frequency events

Abstract

Quantitative risk assessments (QRAs) are used within the field of process safety to decide the allocation of resources and risk reduction investments. 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 risk. 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 mean assessed risk represents an acceptable risk while overlooking the possibility that a single scenario could represent an intolerable event. This article looks at an adjustment to traditional QRAs 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. © 2008 American Institute of Chemical Engineers Process Saf Prog, 2009

Classification of risk acceptability and risk tolerability factors in occupational health and safety

“…In addition to the principles and approaches previously indicated, many influential factors impact risk acceptability. These factors, or criteria used to establish if a risk is acceptable or tolerable, are numerous, and many works have focused on this question, namely Vanem (2012), Lind (2002a, Ditlevsen (2003), Henselwood &Phillips (2009), andHuang et al (2013). These factors can differ depending on the countries, the social and organizational cultures, or the industries.…”

“…In public opinion, the potential severity of a risk is a strong criterion in risk acceptability. On the basis of the variable reversibility of the consequences, the risk would be easier to accept when the damages are reversible (Henselwood & Phillips, 2009). Moreover, according to the variable importance of the potential damages of an event, a risk can be seen as intolerable when a unique event can lead to important damages, with no regard to the probability of occurrence of this event.…”

The ALARP principle in process safety

“…However, there is no guarantee that the chosen criteria are sufficiently stringent to account for the uncertainties. A proposal has been made to address uncertainties within the specification of risk tolerance criteria .…”

The interface of functional safety with process safety and risk analysis

“…Indeed, there is an extensive literature on addressing uncertainties in risk analysis . There has also been a proposal to address the issue within the specification of risk tolerance criteria . Uncertainties should be addressed in using any SIL determination method.…”