Fire Sprinkler Systems
A fire sprinkler system is an active fire protection measure, consisting of a water supply system, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected. Sprinklers may be required to be installed by building codes, or may be recommended by insurance companies to reduce potential property losses or business interruption.
While there is very little specific federal legislation regarding building codes, which are generally left to local jurisdictions, the federal government has used its funding and monetary clout to strongly encourage fire safety standards in construction. Since 2011, two states, California and Pennsylvania have required sprinklers in at least some new residential construction.
In 1990 the US Congress passed PL-101-391, better known as "The Hotel and Motel Safety Act (of 1990)". This law requires that any hotel, meeting hall, or similar institution that receives federal funds (i.e. for a government traveller's overnight stay, or a conference, etc.), must meet fire and other safety requirements. The most visible of these conditions are the implementation of sprinklers.
As more and more hotels, etc., upgraded their facilities to enable acceptance of government visitors, this type of construction became the de facto industry norm - even when not directly mandated by any local building codes. If building codes do not explicitly mandate the use of fire sprinklers, the code often makes it highly advantageous to install them as an optional system. Most US building codes allow for less expensive construction materials, larger floor area limitations, longer egress paths, and fewer requirements for fire rated construction in structures protected by fire sprinklers. Consequently, the total building cost is often less by installing a sprinkler system and savings money in the other aspects of the project, as compared to building a non-sprinklered structure. In the UK, since the 1990s sprinklers have gained recognition within the Building Regulations (England and Wales) and Scottish Building Standards and under certain circumstances, the presence of sprinkler systems is deemed to provide a form of alternative compliance to some parts of the codes. For example, the presence of a sprinkler system will usually permit doubling of compartment sizes and increases in travel distances (to fire exits) as well as allowing a reduction in the fire rating of internal compartment walls.
Wet Pipe Systems
By a wide margin, wet pipe sprinkler systems are installed more often than all other types of fire sprinkler systems. They also are the most reliable, because they are simple, with the only operating components being the automatic sprinklers and (commonly, but not always) the automatic alarm check valve. An automatic water supply provides water under pressure to the system piping.
Dry Pipe Systems
Dry pipe systems are installed in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, rendering the system inoperable.
Operation - Water is not present in the piping until the system operates. The piping is filled with air below the water supply pressure.
"Deluge" systems are systems in which all sprinklers connected to the water piping system are open, in that the heat sensing operating element is removed, or specifically designed as such. These systems are used for special hazards where rapid fire spread is a concern, as they provide a simultaneous application of water over the entire hazard. They are sometimes installed in personnel egress paths or building openings to slow travel of fire (e.g., openings in a fire-rated wall).
Pre-action sprinkler systems are specialized for use in locations where accidental activation is undesired, such as in museums with rare art works, manuscripts, or books; and Data Centers, for protection of computer equipment from accidental water discharge.
Pre-action systems are hybrids of wet, dry, and deluge systems, depending on the exact system goal. There are two main sub-types of pre-action systems: single interlock, and double interlock.
Most Sprinkler systems installed today are designed using an area and density approach.