The Guidelines in this book characterize when and how to apply enabling conditions and conditional modifiers to Layer of Protection Analyses (LOPAs). A LOPA may have consequences and risk criteria expressed in final endpoint (impact) terms such as fatalities or environmental damage, and include conditional modifiers such as probability of fatality associated with a material or energy release. It may also take into account probabilities called enabling conditions that sometimes apply to scenario initiating events. One way to differentiate these two factors is that enabling conditions are associated with the part of an incident sequence leading up to a release of hazardous material or energy, whereas conditional modifiers are probabilities generally associated with the post-release part of an incident sequence.
