PAP-LOPA - I. Introduction The process industry is...

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I. Introduction The process industry is obligated to provide and maintain a safe, working environment for their employees. Safety is provided through inherently safe design and various safeguards, such as instrumented systems, procedures, and training. During a HAZOP, the team is responsible for assessing the process risk from various process deviations and determining the consequence of potential incidents. The team identifies the safeguards used to mitigate the hazardous event. If the team determines that the safeguards are inadequate, the team will make recommendations for further risk reduction. The team is instructed to list all safeguards. The team often lists safeguards that only partially mitigate the process risk. The team also does not address whether the safeguards are independent from one another. This often results in the team assuming more risk reduction from the safeguards than is possible based on the integrity of the individual components. Furthermore, a team’s perception of the integrity of a specific safeguard impacts the assumed risk reduction for that safeguard, resulting in inconsistency in the number of required safeguards for successful mitigation of the process risk. Unfortunately, the inconsistency can result in over- and under- protected process risk, depending on the team composition. Consequently, there must be an independent engineering assessment of the safeguards to ensure that adequate risk reduction is being provided. II. What Is LOPA? LOPA is a semi-quantitative risk analysis technique that is applied following a qualitative hazard identification tool such as HAZOP. We describe LOPA as semi-quantitative because the technique does use numbers and generate a numerical risk estimate. However, the numbers are selected to conservatively estimate failure probability, usually to an order of magnitude level of accuracy, rather than to closely represent the actual performance of specific equipment and devices. The result is intended to be conservative (overestimating the risk), and is usually adequate to understand the required SIL for the SIFs. If a more complete understanding of the risk is required, more rigorous quantitative techniques such as fault tree analysis or quantitative risk analysis may be required. LOPA starts with an undesired consequence – usually, an event with environmental, health,
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safety, business, or economic impact. The general format of a LOPA table is shown in Table 1. The severity of the consequence is estimated using appropriate techniques, which may range from simple “look up” tables to sophisticated consequence modeling software tools. One or more initiating events (causes) may lead to the consequence; each cause-consequence pair is called a scenario. LOPA focuses on one scenario at time. The frequency of the initiating event is estimated (usually from look-up tables or historical data). Each identified safeguard is evaluated for two key characteristics: • Is the safeguard effective in preventing the scenario from reaching the consequence? • AND, is the safeguard independent of the initiating event and the other IPLs (Independent
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This note was uploaded on 02/18/2010 for the course CHEMENG pap taught by Professor Sumardi during the Spring '10 term at Imperial College.

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PAP-LOPA - I. Introduction The process industry is...

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