Open Type Water Spray Systems are generally used for special fire protection applications wherein Standard Sprinkler System is not suitable. These are basically used for fire control, extinguishing, cooling, prevention and/or exposure protection of industrial hazardous locations, typically outdoor. NFPA 15 (Standard for Water Spray Fixed systems for Fire Protection) is generally referred for designing Open Type Water Spray Fixed Systems.
These systems require water to be rapidly applied on all protected surfaces at the same time, which is not possible by closed sprinklers. Therefore various water spray nozzles having directional water discharge capability are used in this case. This is achieved by choosing proper open type nozzles with suitable spray angles. The placement of open nozzles have to be made in such a way that proper water spray coverage is achieved. Water spray application rates are chosen as per NFPA 15 guidelines and suitable K-factor of nozzles is chosen. Hydraulic calculations are to be conducted as part of designing of the system, appropriate piping has to be selected to offer required pressure and flow at each open nozzle for proper and effective water spray pattern. While the system demand has to be considered wherein all open nozzles are operated simultaneously. If total discharge of water into design area is below calculated requirements, add additional nozzles.
Extinguishing methods of Open Type Water Spray systems consist of Surface Cooling, Smothering by Steam Production, Emulsification, and Dilution (extinguishment by dilution of water miscible materials).
In these systems, a separate detection mechanism is used, which automatically actuates a Deluge Valve, in order to achieve rapid system actuation of Open-Type Water Spray System. As per NFPA the system actuation valves have to be placed as close as it is practical to the spray system.
These systems are commonly used in protection of Vessels, Metal Pipes and Conduits, Cable Trays and Cable Runs, Transformers, Vertical Structures, Conveyor Belts, etc.