Foam-Water Sprinkler Systems

Water Spray System Design Methodology

We have compiled some very basic points for effective designing of a water spray system. For more detailed information, refer to NFPA 15, which is the Standard for Water Spray Fixed Systems for Fire Protection. Water Spray Systems are basically used for fire control, extinguishing, cooling, prevention and/or exposure protection of industrial hazardous locations.
As per NFPA 15, for a typical water spray system, the design density of spray ranges from 4.1lpm/sq.m to 20.4 lpm/sq.m – depending on the application and hazard type. The minimum operating pressure of any nozzle protecting an outdoor hazard is stipulated at 20 psi (1.4 bar).
Major steps in designing effective water spray system
  • Establish design area (area to be sprayed)
  • Determine dimensions
  • Determine water density (application rate)
  • Calculate water demand
  • Establish nozzles required (K-factor & Spray Angle)
  • Determine Nozzle Orientation
  • Determine number and type of nozzles required to give adequate water coverage
  • Adjust K-factor & Spray angle - Recalculate
  • Finalize the design
Water Spray Application Rates – Design Density (as per NFPA-15)
Design Objective Hazard Type LPM / Sq. Meter
Exposure Protection
Vessel surface 10.2
Horizontal structural steel 4.1
Vertical structural steel 10.2
Cable trays / runs 12.2
Transformers 10.2
General 20.4
Conveyor belts 10.2
Control of Burning
Pumps and compressors 20.4
Liquid pool fires 12.2
In our next blog, we will specifically discuss about one of the most common applications of fixed water spray system, which is fire protection of flammable liquid and gas storage tanks.