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

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-103
p) STEP 8.16—For each hole size, determine the component damage and personnel injury flammable
consequence areas, flam
flam
CA and
f , cmd , n
CA , using Equation (3.176) and Equation (3.177), respectively.
f , inj,
n
Use the probability of each event outcome, as determined in STEP 8.10, and the consequence area of
each of the event outcomes, as determined in STEPs 8.11 through 8.15.
q) STEP 8.17—Determine the final consequence areas (probability weighted on release hole size) for
component damage, flam
flam
CA , and personnel injury,
f , cmd
CA , using Equation (3.178) and Equation
f , inj
(3.179), respectively.
5.9 Determine Toxic Consequences
5.9.1 General
To evaluate fluids in addition to the 14 provided in Level 1, as well as use of other published toxic criteria
(IDLH, ERPG, AEGL), a Level 2 consequence analysis is required.
Toxic consequence procedure consists of performing a cloud dispersion analysis (see Section 5.7.4) to
determine the extent and duration of the portions of the cloud that remain above the toxic impact criteria
acceptable for the particular toxin being evaluated. The vapor source rate to be used as input to a cloud
dispersion analysis either from a jet release or from evaporation off of a liquid pool is discussed in Section
5.7.4.
5.9.2 Toxic Impact Criteria
5.9.2.1 General
Table 4.14 provides toxic impact criteria for specific toxic fluids modeled in this methodology. Consequence
areas are determined for toxic releases by comparing the cloud concentration to various published toxic impact
criteria. In addition to probit equations, published criteria available for a fluid under consideration can be used.
When multiple published criteria are available, the consequence area should be based on the following
prioritization:
a) probit analysis or LC50;
b) ERPG-3, AEGL-3, or TEEL-3;
c) IDLH or EPA Toxic Endpoint.
This order was established to best represent the 50 % fatality rule used for determining the consequence area.
Group a) represents the consequence of 50 % fatality, group b) represents the lower fatality limit, or 0 % fatality,
and group c) represents the limit in which non-fatal long-term health issues will arise.
5.9.2.2 Probit Analysis
Probit equations [29] provide a simple way of expressing probability of fatality due to exposure of personnel to
concentrations and dosages of toxic releases. Coefficients for probit equations are provided for common toxic
in Table 4.14. The probit equation and some background into its use are provided in Annex 3.A.
5.9.2.3 IDLH
The IDLH air concentration values used by the National Institute for Occupational Safety and Health (NIOSH)
as respirator selection criteria were first developed in the mid-1970s. The documentation for IDLH
concentrations is a compilation of the rationale and sources of information used by NIOSH during the original
determination of 387 IDLHs and their subsequent review and revision in 1994.