Risk management based on the assessment of safety barriers

Abstract

The present paper deals with safety barriers, describing their characteristics and presenting a new classification for them based on their type and operating mode. While the assessment of safety barriers performance is often achieved by tests or inspections in order to determine the probability of failure on demand (PFD) and detect the so-called hidden failures, a new methodology to evaluate the adequacy of a safety barrier is proposed by linking the safety integrity level of an assessed safety barrier with the probability of occurrence of the hazardous event that it should protect. Based on the study of all possible safety function failures there is a selective approach to determine the ones classified as dangerous undetected in a way to use them on the determination of the PFD. Applying the methodology proposed it is also possible to estimate the probability of occurrence of a hazardous situation, once it depends on the simultaneity of happening the initiating event and the safety barrier fault, when a demand occurs. The impact of a specific safety barrier assessment on risk can thus be evaluated.