Chapter 10 - Risk Assessment (QRA)

Abstract

This chapter discusses risk assessment or analysis of a hazard. Risk analysis involves two types of assessment: the frequency of the event and the consequences of the event. Quantified risk assessment (QRA) refers to assessing the frequency of an event and its measurable consequences, such as fatalities or damage. The analysis of consequence is a specialist area within each industry and may be based on chemical, electrical, gas or nuclear technology. Prediction of frequency however is essentially the same activity as reliability prediction. The perception of risk, ALARP (As Low As Reasonably Practicable) and cost per life saved are discussed. When quantifying the risk of fatality, the terms, tolerable, acceptable and unacceptable are important, because as such there is no zero risk. In this context, acceptable generally mean that the probability of fatality is accepted as reasonable, having regard to the circumstances. Tolerable on the other hand, implies that the particular risk level is accepted while continuing to review its causes and the defenses that can be taken to reduce it further.