Deluge & Equipment Cooling System Sizing
NFPA 15: Vessel/tank cooling = 0.25, Structural steel = 0.10
NFPA minimum: 4 hours for industrial facilities
Understand fire protection philosophy, NFPA standards, deluge system design, and fire water pump selection
Fire water demand is the total flow rate (gpm) of water required to cool equipment and protect structures during a fire event. It includes equipment cooling water (applied via deluge or spray systems at 0.25 gpm/ft2 per NFPA 15), hose stream allowances (typically 500 gpm), and a pump margin (10%). Total demand drives fire pump sizing and water storage tank capacity.
Wetted area depends on equipment type. For horizontal vessels, it is the cylindrical shell area plus half of both heads. For vertical vessels, it is the shell area up to 25 ft above grade per NFPA 15. For atmospheric tanks, it is the shell area (no roof). For spheres, approximately 55% of the total surface area is used. Only the area below 25-30 ft above grade is considered exposed to fire.
Per NFPA 15 Table 5.3.2.4, the minimum application density for vessel and tank cooling is 0.25 gpm/ft2. Structural steel protection uses 0.10 gpm/ft2. These densities ensure adequate film coverage to prevent steel temperature from reaching failure limits during fire exposure.
NFPA standards recommend a minimum 4-hour fire water supply duration for industrial facilities. Some jurisdictions or project specifications may require 6-8 hours. The total storage volume equals total demand (gpm) multiplied by duration (minutes). A typical midstream facility may need 500,000 to 2,000,000 gallons of fire water storage.