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

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-89
Fh
n
⎛
⎞
⎜ 1 ⎡
−1
Y + 1⎤
⎟
⎜ tan ⎢ ⎥−
π Y −1
⎟
⎜ ⎣ ⎦
⎟
⎜ 2
2
⎛ ⎟
X + ( Y + 1) − 2( Y + 1+ XY sinθ
pf , n ) ⎞ ⎡
1
A′ − ( Y −1)
⎤
=
⎜⎜
⎟⋅ tan ⎢ ⎥+
⎟
⎜⎜ π AB ′ ′ ⎟ ⎢ B′
( Y + 1)
⎥
⎟
⎜⎝
⎠ ⎣ ⎦ ⎟
⎜
2 2
sinθ
⎛ XY
, 1
( Y 1)
sinθ
pf n
pf , n sinθ
1 pf , n
Y 1 ⎞
⎟
⎜⎛
⎞ ⎡ − − ⎤ ⎡
− ⎤
−
−
⎟
⎜ ⎟⋅ ⎜tan
⎢
⎥+
tan ⎢
⎥⎟
2
⎜
π C′ ⎜
Y 1 C
⎢ C′
⎥⎟⎟
⎝ ⎠ ⎢⎣ − ′ ⎥
⎝ ⎝
⎦ ⎣ ⎦⎠⎠
(3.144)
In Equation (3.143) and Equation (3.144), the following parameters are used.
X
Y
L
pf , n
= (3.145)
R
xs
R
pf , n
n
= (3.146)
pf , n
2
( ) ( )
′ = + + 1 − 2 + 1 sin pf n
(3.147)
2
A X Y X Y θ
,
2
( ) ( )
′ = + −1 −2 − 1 sin pf n
(3.148)
2
B X Y X Y θ
,
( )
C′ = + Y − θ
(3.149)
2 2
1 1 cos
pf , n
5.8.2.6 Pool Fire Safe Distance and Consequence Area
The procedure for determining the consequence area associated with a pool fire consists of calculating the
distance away from the pool fire where the radiated energy from the pool fire is equal to the exposure limits
(impact criteria) for thermal radiation as provided in Section 4.8.2. A maximum permissible radiation of
12.6 kW/m 2 (4,000 Btu/hr-ft 2 ) is used for serious personnel injury. The maximum permissible radiation for
component damage is 37.8 kW/m 2 (12,000 Btu/hr-ft 2 ).
Note that the atmospheric transmissivity and the source view factor are functions of the distance from the flame
source to the target. These are the two parameters that account for the fact that the received thermal radiation
at any point away from the fire goes down as the distance increases. An iterative approach is required to
determine the acceptable or safe distance away from the pool fire.
This procedure is carried out for personnel injury as well as component damage for each of the release hole
sizes selected as described in Section 4.2. Once the safe distances, pool
pool
xs and
cmd , n
xs , are determined,
inj,
n
Equation (3.150) and Equation (3.151) are used to calculate the pool fire consequence areas.
pool
( ) 2
CA = π ⋅ xs + R
(3.150)
pool
f , cmd , n cmd , n pf , n
pool
( ) 2
CA = π ⋅ xs + R
(3.151)
pool
f , inj, n inj, n pf , n