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

3-102 API RECOMMENDED PRACTICE 581
2) For the component damage consequence area, an overpressure limit of 34.5 kPa
vce
xs cmd n
(5.0 psi). This overpressure limit is used to determine the safe distance,
,
, from the VCE using
the following four-step iterative procedure.
vce
i) Guess at an acceptable component damage distance from the VCE, xs .
cmd , n
ii) Calculate the Hopkinson-scaled distance, R , using Equation (3.171). This parameter is a
HS , n
vce
function of the distance from the VCE chosen above, xs .
cmd , n
iii) Calculate the side-on overpressure, P , at the Hopkinson-scaled distance,
SO,
n
R
,
Equation (3.170).
HS n
, using
vce
iv) Adjust the distance, xs , accordingly, and repeat the above steps until the side-on
cmd , n
overpressure, P , is equal to 34.5 kPa (5.0 psi).
SO,
n
vce
3) Calculate the component damage consequence area, CA , using Equation (3.173).
f , cmd , n
4) A probit equation based on building collapse is used for personnel injury consequence area and is
detailed in Section 5.8.5.5. This probit equation is used to determine the safe distance, vce
xs , from
inj , n
the VCE using the following five-step iterative procedure.
vce
i) Guess at an acceptable personnel injury distance from the VCE, xs .
inj,
n
ii) Calculate the Hopkinson-scaled distance, R , using Equation (3.171). This parameter is a
HS , n
vce
function of the distance from the VCE chosen above, xs .
inj,
n
iii) Calculate the side-on overpressure, P , at the Hopkinson-scaled distance,
SO,
n
R
,
Equation (3.170).
iv) Calculate the probit value, Pr , using Equation (3.172).
HS n
, using
vce
v) Adjust the distance, xs , accordingly, and repeat the above steps until the probit value is
cmd , n
equal to 5.0.
vce
5) Calculate the personal injury consequence area, CA , using Equation (3.174).
f , inj,
n
flash
o) STEP 8.15—For each of the hole sizes, calculate the component damage consequence area, CA ,
f , cmd , n
flash
and the personnel injury consequence area, CA
, ,
f inj n
, of a flash fire.
1) Using the vapor source rate and source area determined in STEP 7.7, perform a cloud dispersion
analysis in accordance with Section 5.7.4 and determine the grade level area or boundary of the cloud
that is at or above the LFL of the mixture in the cloud. This grade level area is equal to the personnel
injury consequence area, flash
CA .
f , inj , n
flash
2) The component damage consequence area for the flash fire, CA , is 25 % of personnel injury
f , cmd , n
flash
consequence area CA , in accordance with Equation (3.175).
f , inj,
n