References to follow for Water Spray Fixed System
- NFPA 15:
- Standard for Water Spray Fixed Systems for Fire Protection
- NFPA 14:
- The standard for the Installation of Standpipe and Hose Systems
- NFPA 24:
- The standard for the Installation of Private Fire Service Mains and Their Appurtenances
- NFPA 20:
- The standard for the Installation of Stationary Pumps for Fire Protection
- NFPA 25:
- The standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems
Water Spray Fixed System: What it is?
NFPA 15 Says
Water Spray System is an automatic or manually actuated fixed pipe system connected to a water supply and equipped with water spray nozzles designed to provide a specific water discharge and distribution over the protected surfaces or area. [3.3.21, Page 15-7, 2007 Edition]
A water spray fixed system sometimes called a deluge system is a total flooding system. Therefore, its operation differs from the sprinkler system. A sprinkler system is only activated when it reaches its predefined or rated temperature, most of the cases it is one sprinkler at a time. But in this system, a detection system triggers a zone of spray nozzles. Apart from a pumping unit and a pipe network, a water spray fixed system consists of the following
- Nozzle
- Deluge or Actuating type Butterfly valve
- Quartzoid Bulb sprinkler/other detection systems
When to select water spray system
Normally, the system can attain any one of or a combination of the following objectives :
- Extinguishment of fire: generally used for Cable Trays and Cable Runs, Belt Conveyors, etc.
- Control of burning: For Pumps, Compressors, and Related Equipment and Flammable and Combustible Liquid Pool Fires.
- Exposure protection: For vessels, Structures, and Miscellaneous Equipment, Transformers, etc.
- Prevention of fire: For dissolving, diluting, dispersing, or cooling of flammable vapor, gases, or hazardous materials.
System Design
Fixed spray Systems should operate automatically with the presence of supplementary manual tripping means. If a system is isolated and attended 24/7 by trained personnel than the only manual operation is ok.
The system design should work in such a way through water spray from all open nozzles operate without delay. The nozzle spray pattern definitely needs to overlap. Nozzle spacing (vertically or horizontally) shall not exceed 10 ft (3 m) or it can if the nozzle is listed otherwise.
Size of System and Water Demand
A single system shall not protect more than one fire area. The hydraulically designed discharge rate for a single system or multiple systems designed to operate simultaneously shall not exceed the available water supply. The following factors determine the number of systems expected to operate simultaneously
(1) The possible flow of burning liquids between areas before or during operation of the water spray systems
(2) The possible flow of hot gases between fire areas that could actuate adjoining systems, thereby increasing demand.
(3) Flammable gas detection set to automatically actuate systems
(4) Manual operation of multiple systems
(5) Other factors that obviously result in the operation of systems outside of the primary fire area
Generally, hydraulic calculation is used as part of the design of the piping system to determine that the required pressure and flow are available at each nozzle. The minimum operating pressure of any nozzle protecting outdoor hazard shall be 20 psi (1.4 bar).
