Water requirement in tank farm fire

The adequate fire protection of storage vessels to guard against their catastrophic failure is recognised to be of key importance. The radiant energy flux from large open hydrocarbon fires can be sufficiently high to threaten the structural integrity of neighbouring structures, equipment, or storage tanks. This work deals with the protection of an adjoining tank from a tank on fire by the use of water-spray system. The amount of radiative heat flux falling on the adjoining tank is first calculated and is then used to determine the amount of water required to prevent any serious temperature rise in the adjoining tank. Assuming pool fire in the tank farm with no wind condition, smokeless flame and no atmospheric attenuation of radiant heat, the amount of water required to save the adjoining tank varies from 0.091 l/m2 s to 0.243 l/m2 s (5.5 l/m2 min to 14.6 l/m2 min) depending upon the relative size of tank and the adjoining tank at a fixed distance. The value recommended by NFPA-15 is 0.17 l/m2 s (10.2 l/m2 min) for all tank sizes. This is almost 90% more at one end and 30% less at the other end of spectrum of tank sizes considered here. Using excess water results in waste and excessive post-use water clean up costs. Using less than required amount results in inadequate cooling of the adjoining tank and hence its integrity may be put in doubt.