(84c) Fire Impairment Analysis for Designing Offshore Depressurization System.

Emergency depressurization system in an offshore facility is a critical safety system to dispose pressurized fluids to flare or vent to prevent escalation of a fire scenario. The design of the depressurizing system shall be adequate to ensure the stress of the protected vessel or system is
not compromised. According to API 521, depressurizing a system to 7 barg in 15 minutes is commonly considered to reduce the consequences from vessel failure. This can be challenging for a brownfield facility where the vent or flare capacity is limited. Moreover, with most offshore
facilities aiming for remote operations with minimal manning, the design of emergency system calls for practical design of fit for purpose.

The selection of type of depressurizing system whether to depressurize within 15 minutes or longer is dependent on risk evaluation supported with analysis to demonstrate that the risks can be mitigated to as low as reasonably possible (ALARP). This paper presents the detailed approach on how a brownfield project implemented fire impairment analysis to assess the impact to sensitive receptors and the duration of impact that could affect the escape and evacuation during emergency. These results provide a basis to decide a practical depressurization duration and
requirement for automatic or manual depressurization system.