Skip to main content

Calculation of Water Spray for Fire Protection of Vertical Vessel


I just got an assignment from my boss to calculate fire protection of vertical vessel. NFPA 15 (National Fire Protection Association 15) is a standard for water spray fixed system for fire protection.

Definition

As per NFPA 15, water spray refer to the use of water in a form of having a predetermined pattern, particle size, velocity, and density discharged from specially designed nozzle devices.

Standards for Vessels

The following standards from NFPA 15 are applicable to the protection of vessels.

7.4 Exposure Protection

7.4.1 General. A system for exposure protection shall operate as intended for anticipated duration of the exposure fire

7.4.2 Vessels

7.4.2.1 Water spray shall be applied to vessel surfaces (including top and bottom surfaces of vertical vessels) at a net rate of not less than 0.25 gpm/ft2 [10.2 (L/min)/m2] of exposed surface

7.4.2.2 When rundown  is contemplated, the distance between nozzles at different levels or elevations, protecting vertical or inclined surfaces, shall not exceed 12 ft (3.7 m) as measured along the surface

7.4.2.3 The horizontal distance between nozzles shall be such that spray patterns meet or overlap at the protected surface

7.4.2.4 Spherical or horizontal cylindrical surfaces below the vessel equator shall not be considered wettable from rundown

7.4.2.5 Where projections (manhole flanges, pipe flanges, support brackets, relief valves, etc) will obstruct water spray coverage, including rundown on vertical surfaces, additional nozzles shall be installed around the projections to maintain the wetting pattern that otherwise would be seriously interrupted

7.4.2.6 All uninsulated vessel skirts and any uninsulated steel saddles greater than 12 in (305 mm) high at the lowest point shall have water spray applied on one exposed (uninsulated) side, at a net rate of not less than 0.25 gpm/ft2 [10.2 (L/min)/m2]

As per NFPA 15, operating pressure at the hydraulically farthest nozzle shall not be allowed to drop below 50 psi (3.5 bar).

On this post, I try to make calculation excel of water sprayer for vertical vessel with cone roof. I hope you find the excel is useful.

Water sprayer calculation for vertical vessel

One thought to “Calculation of Water Spray for Fire Protection of Vertical Vessel”

  1. Please advise:
    what will be the effect of adjusting sprinkler header by 0.6m from where it was design with 60 degrees,application rate 10L.min.m2?
    vessel lenght=7.62m,surface area=30m2

    thanks to your response
    daniel

Leave a Reply