Automatic Sprinkler System Calculations – Introduction
Applications Where Water Is Appropriate
Water is the most commonly used fire extinguishing agent, mainly due to the fact that it is widely available and inexpensive. It also has very desirable fire extinguishing characteristics such as a high specific heat and high latent heat of vaporization. A single gallon of water can absorb 9280 Btus (2586.5 kJ) of heat as it increases from a 70ÜF (21ÜC) room temperature to become steam at 212ÜF (100ÜC).
Water is not the perfect extinguishing agent, however, and is considered inappropriate for the protection of
Certain water reactive materials. In some cases, the use of water can produce heat, flammable or toxic gases, or explosions. The quantities of such products must be considered, however, because application of sufficient water can overcome the reaction of minor amounts of these materials.
Another drawback of water is that it is more dense than most hydrocarbon fuels, and immiscible as well. Therefore, water will not provide an effective cover for burning hydrocarbons, or mix with them and dilute them to the point of not sustaining combustion. Instead, the hydrocarbons will float on top of the water, continuing to burn and possibly spread. To combat such fires, foam solutions can be introduced into the water to provide an effective cover and smother the fire. Applying water in a Fine mist has also been successful.
However, even when water from sprinklers will not suppress the fire, its cooling ability can protect structural elements of a building by containing the fire until it can be extinguished by other means
Types of Sprinkler Systems
- A wet pipe system is by far the most common type of sprinkler system. It consists of a network of piping containing water under pressure. Automatic sprinklers are connected to the piping such that each sprinkler protects an assigned building area. The application of heat to any sprinkler will cause that single sprinkler to operate, permitting water to discharge over its area of protection.
- A dry pipe system is similar to a wet system, except that water is held back from the piping network by a special dry pipe valve. The valve is kept closed by air or nitrogen pressure maintained in the piping. The operation of one or more sprinklers will allow the air pressure to escape, causing operation of the dry valve, which then permits water to flow into the piping to suppress the fire. Dry systems are used where the water in the piping would be subject to freezing.
- A deluge system is one that does not use automatic sprinklers, but rather open sprinklers. Aspecial deluge valve holds back the water from the piping, and is activated by a separate fire detection system. When activated, the deluge valve admits water to the piping network, and water flows simultaneously from all of the open sprinklers. Deluge systems are used for protection against rapidly spreading, high hazardfires.
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