TABLE OF CONTENTS Although risk may be assessed in both a qualitative and quantitative way, this book primarily deals with quantitative methods. Thus qualitative risk assessment and safety review methods are not covered explicitly in this chapter, which provides a brief overview of QRA. Further details are presented in the following chapters.
'Risk analysis' is defined in the NORSOK standard (NORSOK, 1998) as an analysis which includes a systematic identification and description of risk to personnel, environment, and assets. The ISO definition (ISO, 2002) is 'systematic use of information to identify sources and assign risk values'. QRA therefore has to be focused on:
Identification of applicable hazards.
Description (including quantification) of applicable risks to personnel, environment, and assets.
The analytical elements of risk assessment are those that are required to identify the relevant hazards and to assess the risk arising from them. These elements may include all, or some, of the following:
Identification of initiating events
Cause analysis
qualitative evaluation of possible causes
probability analysis in order to determine the probability of certain scenarios
Consequence analysis
consequence loads, related to physical effects of accidents
response analysis, related to response of the facilities, when exposed to accidental loads
probability analysis, related to the probability that these loads and responses occur
quantification of consequences in terms of injury to personnel, damage to environment and/or to assets.
The elements of QRA are shown diagrammatically in Figure 5.1. This diagram is sometimes called the 'Bow-tie diagram' for obvious reasons.
