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Flare Quantitative Risk Analysis (QRA) is a systematic approach to determine the adequacy of a flare header and can be applied to provide a more realistic assessment of the risk associated with vessel accumulation due to common mode scenarios, in accordance with American Petroleum Institute (API) Standard 521. The QRA process takes the results of a traditional flare study and adds QRA inputs. These include the frequencies of the common mode scenarios, and the effects of instrumentation, operator intervention, and other layers of protection that tend to reduce the severity of the common mode scenario. The process generates a system risk profile, such as an accumulation versus frequency relationship for each vessel discharging to the relief header, which in turn can provide an estimate of the risk of catastrophic loss of containment associated with the relief header system. Flare QRA may reduce costs associated with the need to retrofit flare headers or construct new ones.
Experience has shown there are several challenges when performing QRA, including (a) how the system level risk is defined, (b) verification of reliability data used as QRA inputs, and (c) how considering only individual equipment may skew the view of resulting risk. This paper discusses these challenges, as well as what results can be expected from Flare QRA and what issues (e.g., flare tip) are not addressed through this analysis process.