Risk management in the petrochemical industry includes a wide variety of activities, one of which is quantitative risk assessment. The quality of a quantitative risk assessment study is highly dependent on the effectiveness of the hazard identification stage - it is essential that all applicable hazards and potential hazard scenarios are considered. When analyzing large refineries, the number of hazard scenarios can run into thousands; so it is important that these hazard scenarios have a relevant risk impact on the study results, while excluding those scenarios with negligible risk contribution. Two general types of scenarios leading to loss of containment are typically considered: "generic" and "non-generic".

This paper outlines and describes a tool to enhance operational risk management - it describes an effective methodology for streamlining hazard scenario identification and development for large, site wide, refinery quantitative risk assessments. The paper also provides practical guidance for the estimation of both "generic" and "non-generic" scenario failure rate data. Safeguards such as basic process controls and safety instrumented systems that can be used to mitigate undesirable events and to reduce risks are considered in the scenario identification and development methodology.

An Overview of Risk

Risk, as it relates to the process industries, has been defined as a measure of economic loss or human injury in terms of both the incident likelihood and the magnitude of the loss or injury. A simplified risk equation could be represented by:

Risk = Consequence x Frequency (1)

A risk analysis is the development of a quantitative estimate of risk, based on engineering evaluation and mathematical techniques for combining estimates of incident consequences and frequencies.

Quantified Risk Assessment (QRA) can be used for a number of different purposes. However, it is most valuable as part of a Risk Management program. Risk Management is the identification and control of hazards, through both technological and management solutions. Occasionally QRA is conducted solely to meet a regulatory requirement, but this rarely precludes using the results as part of a corporate risk management program.

A QRA can typically be divided into four primary tasks, and a reporting activity. The primary tasks being:

  • Hazard Identification

  • Frequency Analysis

  • Hazards Analysis

  • Risk Determination

The purpose of this paper is to describe an effective methodology for efficiently streamlining hazard scenario identification and development, for large refinery quantitative risk assessments. Therefore, focus will be directed to the hazard identification stage.

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