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

3-122 API RECOMMENDED PRACTICE 581
xs is the safe distance from the VCE for personnel injury associated with the n th release hole size,
vce
inj,
n
m (ft)
vce
xs
n
is the safe distance from the VCE associated with the n th release hole size,
m (ft)
X is the surface roughness factor, unitless
surf
α is the thermal diffusivity of the surface under the liquid pool, m 2 /s (ft 2 /s)
surf
β
is the fraction of combustion power radiated from a flame
β is the fraction of combustion power radiated from a fireball
fb
∆ H v
is the latent heat of vaporization of the liquid in the pool, J/kg (Btu/lb)
η
is the explosion yield factor, unitless
ρ
atm
is the atmospheric air density, kg/m 3 (lb/ft 3 )
ρ
l
is the liquid density at storage or normal operating conditions, kg/m 3 (lb/ft 3 )
ρ
v
is the vapor density at storage or normal operating conditions, kg/m 3 (lb/ft 3 )
θ is the pool fire flame tilt associated with the n th release hole size, radians
pf , n
τ
atm
is the atmospheric transmissivity, unitless
τ is the atmospheric transmissivity associated with the n th release hole size, unitless
atm,
n