API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-3
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3 General
3.1 Overview
The COF methodology is performed to aid in establishing a ranking of equipment items on the basis of risk.
The consequence measures presented in Part 3 are intended to be used for establishing priorities for
inspection programs. Methodologies for two levels of analysis are provided. A Level 1 COF methodology is
detailed in Section 4 for a defined list of hazardous fluids. A Level 2 COF methodology is provided in Section 5,
which is intended to be more rigorous and can be applied to a wider range of hazardous fluids. A special COF
methodology is provided for ASTs and is covered in Section 6.
3.2 Consequence Categories
The major consequence categories are analyzed using different techniques, as follows.
a) Flammable and explosive consequence is calculated using event trees to determine the probabilities of
various outcomes [e.g. pool fires, flash fires, vapor cloud explosions (VCEs)], combined with computer
modeling to determine the magnitude of the consequence. Consequence areas can be determined based
on serious personnel injuries and component damage from thermal radiation and explosions. Financial
losses are determined based on the area affected by the release.
b) Toxic consequence is calculated using computer modeling to determine the magnitude of the consequence
area as a result of overexposure of personnel to toxic concentrations within a vapor cloud. Where fluids
are flammable and toxic, the toxic event probability assumes that if the release is ignited, the toxic
consequence is negligible (i.e. toxics are consumed in the fire). Financial losses are determined based on
the area affected by the release.
c) Nonflammable, nontoxic releases are considered since they can still result in serious consequences.
Consequence from chemical splashes and high-temperature steam burns are determined based on
serious injuries to personnel. Physical explosions and BLEVE can also cause serious personnel injuries
and component damage.