(18b) High Demand, Low Demand, and Time at Risk (Important Considerations beyond Basic LOPA)

When performing a LOPA, practitioners need to consider both the type of demand that will occur on the protection system(s) and when the potential risk is actually present. Most LOPA practitioners make the assumption that the initiating event represents a low frequency demand on subsequent layers of protection. This paper addresses some situations where this is not a good assumption and provides guidance with regards to such scenarios. The paper also provides a thought process that can be used to address time at risk, with some guidance as to when it is appropriate to include in the LOPA as well as when it is not.