Risk-Based Approach – Risk Tolerability Criteria

Risk-based quantitative assessment is accepted as a process safety management tool in many countries throughout the world. Risk-based legislation is implemented by national governmental bodies. These organizations are often under public scrutiny, which indicates a high degree of societal endorsement of the values.

There are at least three topics that are commonly used in the development of generally accepted and recognized risk criteria:

1. A comprehensive risk management program must address both individual and societal risk;
2. Risk criteria for the public must be lower, i.e. more conservative, than those for the workforce since the workforce risk is considered to be voluntary; and (
3. New facilities should be held to a higher level of risk performance than existing facilities for individual risk.

For new facilities, many opportunities exist to apply new/advanced risk reduction technologies. In contrast, societal risk criteria are universally identical for new and existing situations. Where a potential exists for major accidents affecting large numbers of people, most regulators have judged that older facilities must meet the same standards as newer facilities.

This paper evaluates various international risk criteria in use today and evaluates their respective merits. It also provides suggestions for companies or countries considering implementing their own risk tolerability criteria.

Introduction

ISO 17776 defines the concept of risk as the combination of the frequency of occurrence of an event and the consequences of that event. Its estimation is used to take decisions usually supported by using graphical tools (e.g., F‐N curve, risk profile, risk contour) to show risk and the relationship between frequencies and consequences. Most of the factors that contribute to the total risk of a process facility, the risk values will highlight the major sources of risk and will give the decision‐maker direction for re‐design or other loss prevention efforts. Quantitative Risk Assessment (QRA) is a technique to achieve this goal (see Figure 01).

Figure 01: Risk Management Program Simplified Flowchart