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

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-25
p) STEP 8.16—Determine the final consequence areas (probability weighted on release hole size) for
component damage and personnel injury using Equation (3.59) and Equation (3.60) based on the
consequence areas from STEP 8.15.
CA
flam
f , cmd
⎛
4
flam
⎜∑
gffn
⋅CAcmd , n ⎟
n=
1
= ⎜
⎟
⎜ gfftotal
⎟
⎜
⎝
⎞
⎟
⎠
(3.59)
CA
flam
f , inj
⎛
4
flam
⎜∑
gffn
⋅CAinj,
n ⎟
n=
1
= ⎜
⎟
⎜ gfftotal
⎟
⎜
⎝
⎞
⎟
⎠
(3.60)
4.9 Determine Toxic Consequence
4.9.1 General
Toxic fluids are similar to flammables in that not all toxic releases result in a single type of effect. By themselves,
hydrogen fluoride (HF), ammonia, and chlorine pose only a toxic hazard. On the other hand, some toxic
materials such as hydrogen sulfide (H2S) are both toxic and flammable. However, any toxic material, when
mixed with hydrocarbons, can pose flammable and toxic hazards.
The toxic consequence is calculated using a hazards analysis in conjunction with atmospheric dispersion
models similar to the flammable procedure described in Section 4.8.
4.9.2 Common Refining Toxic Materials
The procedure for determination of toxic consequence of four toxic materials that typically contribute to toxic
risks for a refinery—hydrogen fluoride (HF), hydrogen sulfide (H2S), ammonia (NH 3 ), and chlorine (Cl)—is
provided in Section 4.9.6 and Section 4.9.7.
4.9.3 Common Chemical Industry Toxic Materials
The determination of toxic consequence includes 10 additional toxic chemicals commonly used in the chemical
industry as described in Section 4.9.8. Level 1 toxic consequence analysis uses probit data for determining
the consequence areas (see Table 4.14).
4.9.4 Representative Fluids for Toxic Mixtures
Modeling of releases where the toxic component is part of a mixture is a special case for the Level 1
consequence analysis. For these cases, the analysis requires the selection of a representative fluid from Table
4.1 for the purpose of determining the release rate that is used in the consequence assessment. The
representative fluid should be selected based upon the average boiling point, density, and MW of the mixture;
see Section 4.1.2. A Level 2 consequence analysis per Section 5 rigorously calculates the fluid composition
and release mixture.