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

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3.A-12 API RECOMMENDED PRACTICE 581b) carbon monoxide (CO);c) hydrogen chloride (HCl);d) nitric acid;e) nitrogen dioxide (NO2);f) phosgene;g) toluene diisocyanate (TDI);h) ethylene glycol monoethyl ether (EE);i) ethylene oxide (EO);j) propylene oxide (PO).The Level 1 consequence analysis equations for these chemicals have been developed using the sameapproach as for ammonia and chlorine, described in Section 3.A.3.6.7 and Section 3.A.3.6.8.3.A.3.6.9.2Continuous ReleasesFor continuous releases, the consequence area can be approximated as a function of duration usingEquation (3.A.9) with the constants e and f provided in Part 3, Table 4.12.3.A.3.6.9.3Instantaneous ReleasesToxic consequences of an instantaneous release for the toxic chemicals listed in Section 3.A.3.6.9.1estimated smaller (or 0) affected areas than equivalent continuous releases. A conservative curve wascalculated using a short duration continuous release toxic consequence curve instead of a less conservativeinstantaneous release area.3.A.3.7 NomenclatureThe following lists the nomenclature used in Section 3.A.3. The coefficients C1through C41that provide themetric and U.S conversion factors for the equations are provided in Annex 3.B.aAbBcCis one-half of the cloud width (minor axis), taken at its largest point (within the 50 % probabilityof fatality dose level)is a constant for the probit equationis one-half of the downwind dispersion distance (major axis), taken at the 50 % probability offatality dose levelis a constant for the probit equationis a constant for the specific consequence area equations for HF acid and H2Sis the toxic concentration in the probit equation, ppmCAfis the consequence area, m 2 (ft 2 )

RISK-BASED INSPECTION METHODOLOGY, PART 3, ANNEX 3.A—BASIS FOR CONSEQUENCE METHODOLOGY 3.A-13CAf , combis the combined/probability weighted consequence area, m 2 (ft 2 )CAf , iis the individual outcome consequence area for the i th event outcome, m 2 (ft 2 )defmassnpiPrratetxyis a constant for the specific consequence area equations for HF acid and H2Sis the constant for the specific consequence area equations for ammonia and chlorineis the exponent for the specific consequence area equations for ammonia and chlorineis the release mass, kg (lb)is the exponent in the probit equationis the specific event probability for the i th event outcome; see Tables 3.A.3.3, 3.A.3.4, 3.A.3.5,or 3.A.3.6is the probit value, typically 5.0, which is defined as 50 % probabilityis the release rate, kg/s (lb/s)is the toxic dosage in the probit equation, secondsis the constant for the generic consequence area equationis the exponent for the generic consequence area equation

RISK-BASED INSPECTION METHODOLOGY, PART 3, ANNEX 3.A—BASIS FOR CONSEQUENCE METHODOLOGY 3.A-13

CA

f , comb

is the combined/probability weighted consequence area, m 2 (ft 2 )

CA

f , i

is the individual outcome consequence area for the i th event outcome, m 2 (ft 2 )

d

e

f

mass

n

p

i

Pr

rate

t

x

y

is a constant for the specific consequence area equations for HF acid and H2S

is the constant for the specific consequence area equations for ammonia and chlorine

is the exponent for the specific consequence area equations for ammonia and chlorine

is the release mass, kg (lb)

is the exponent in the probit equation

is the specific event probability for the i th event outcome; see Tables 3.A.3.3, 3.A.3.4, 3.A.3.5,

or 3.A.3.6

is the probit value, typically 5.0, which is defined as 50 % probability

is the release rate, kg/s (lb/s)

is the toxic dosage in the probit equation, seconds

is the constant for the generic consequence area equation

is the exponent for the generic consequence area equation

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