Where
does Fire and Gas System (FGS) fit in a
LOPA?
Abstract Fire
and Gas Systems provide detection, reduce escalation potential of a hazardous
event and initiate emergency response if required. The FGS layer, in most
cases, do not achieve or maintain safe state for a process but mitigate the
severity of the consequence. However,
while conducting a LOPA, questions arise on how to take credit for a Fire and
Gas System, is it a preventive layer or a conditional modifier, the minimum
Probability of Failure on Demand (PFD) for the FGS layer and whether the PFD is
achievable for a designed and installed FGS layer. This
paper provides insight on these questions and throws light on how to credit a FGS
layer through a case study of a real chemical processing unit. The case study
involves a LOPA scenario where in a FGS system is credited as an IPL or
conditional modifier and is designed and verified using the performance based
fire and gas mapping to obtain the target risk level. The fire and gas mapping
follows the lifecycle approach defined in ISA84.00.07 to place the detectors in
appropriate location to obtain best coverage. Based
on the study, recommendations are provided on how to utilize FGS layer in a LOPA. Keywords ISA TR84.00.07, FGS, LOPA, IPL, Detection, Mapping
See more of this Group/Topical: Global Congress on Process Safety