Hi ,
A fire-case relief load was cut by 70% because the vessel was listed as “adequately insulated.”
Eighteen months later, an inspector found that no insulation had ever been installed!!
That is not a minor construction discrepancy. It can change whether the installed Pressure Safety Valve (PSV) is adequate in a fire.
Under API 521, the environmental factor F reduces the calculated fire heat input when qualified fireproof insulation is present.
Bare vessel:
F = 1.0
Qualified fireproof insulation with conductance of 22.7 W/(m²·K) [4 Btu/(h·ft²·°F)]:
F ≈ 0.3
Because the required fire relief rate is directly proportional to fire heat input, the lower F value can reduce the required relief load by approximately 70%.