Open-type water spray protection systems are typically designed per NFPA 15 or similar design standards and are acceptable for protecting hazards involving; flammable or combustible materials, electrical hazards, propellants, pyrotechnics, and similar life/safety situations. Open-type deluge nozzles and systems typically maintain dry supply piping and the use of heat, smoke, or flame detection equipment to open a deluge valve that supplies water and pressure to the nozzle for operation.

These differ from automatic systems in which automatic nozzles use a heat-sensitive element to maintain a closed orifice and retain the water/pressure of the supply piping system until activated.

There are three general categories for deluge applications:

Cooling

Water is sprayed onto the exterior surface of vessels under pressure and contains volatile materials. The water keeps the contents cool, thereby preventing the contents from increasing in pressure. They are commonly used in tank farms and on any vessel where catastrophic failure from overheating.

Evaporation

Misting nozzles are used to extinguish or control fires by spraying fine droplets onto the flames, which rapidly evaporate, cool, and displace oxygen.

润湿

Water is sprayed to control the spread of a fire but not extinguish it. Wetting is commonly used in gas leak situations where the gas continues to be consumed by the flame until the gas flow is turned off. Extinguishing these types of fires before turning off the gas flow can allow a build-up of flammable gas that can lead to an explosion