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

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-27
4.9.7 Estimation of Toxic Consequence Area for Ammonia and Chlorine
a) The background for the development of the toxic consequence equations for ammonia and chlorine are
provided in Annex 3.A. For determination of the consequence areas, the assumption was made that the
release phase would always be a gas or vapor.
b) The toxic consequence areas for continuous releases of ammonia or chlorine as a function of the release
rate may be calculated using Equation (3.65).
CA
tox−CONT
inj,
n
tox
( n )
f
= e rate
(3.65)
Note that for continuous releases, the toxic release rate,
tox
rate , is used as the input to Equation (3.65).
n
The constants e and f for Equation (3.65) are provided in Table 4.12 as a function of release duration.
Interpolation between curves using the actual duration is acceptable.
c) The toxic consequence areas for instantaneous releases of ammonia or chlorine as a function of the
release rate may be calculated using Equation (3.66).
CA
tox−INST
inj,
n
tox
( n )
f
= e mass
(3.66)
Note that for instantaneous releases, the toxic release mass,
tox
mass , is used as the input to
n
Equation (3.66). The constants e and f for Equation (3.66) are provided in Table 4.12.
4.9.8 Estimation of Toxic Consequence Area for Additional Common Chemicals
q) The background for the development of the toxic consequence equations for 10 additional common
chemicals shown below is provided in Annex 3.A. For determination of the consequence areas, the
assumption was made that the release phase could either be a vapor, liquid, or powder. Additionally, the
consequence equations were developed for continuous release equations only.
1) Aluminum Chloride (AlCl3)—Powder.
2) Carbon Monoxide (CO)—Gas only.
3) Hydrogen Chloride (HCl)—Gas only.
4) Nitric Acid—Gas or liquid.
5) Nitrogen Dioxide (NO2)—Gas or liquid.
6) Phosgene—Gas or liquid.
7) Toluene Diisocyanate (TDI)—Liquid only.
8) Ethylene Glycol Monoethyl Ether (EE)—Gas or liquid.
9) Ethylene Oxide (EO)—Gas only.
10) Propylene Oxide (PO)—Gas or liquid.
r) Procedures for these chemicals have been developed in much the same manner as that for ammonia and
chlorine and are further described in Annex 3.A.