Articles
Fire sprinklers
Fire sprinklers are an active fire protection measure subject to stringent bounding. They are connected to a fire suppression system that consists of overhead pipes fitted with sprinkler heads throughout the coverage area. Fire sprinkler systems for high-rises are usually also equipped with a fire pump, and a jockey pump and are tied into the fire alarm system. Although historically only used in factories and large commercial buildings, home and small building systems are now available at a relatively cost-effective price.
From 1852 to 1885, perforated pipe systems were used in textile mills throughout New England as a means of fire protection. However, they were not automatic systems; they did not turn on by themselves. Inventors first began experimenting with automatic sprinklers around 1860. The first automatic sprinkler system was patented by Philip W. Pratt of Abington, MA, in 1872.
Henry S. Parmalee of New Haven, Connecticut is considered the inventor of the first practical automatic sprinkler head. Parmalee improved upon the Pratt patent and created a better sprinkler system. In 1874, he installed his fire sprinkler system into the piano factory that he owned.
Until the 1940s, sprinklers were installed almost exclusively for the protection of commercial buildings, whose owners were generally able to recoup their expenses with savings in insurance costs. Over the years, fire sprinklers have become mandatory safety equipment, and are required by building codes to be placed in hospitals, schools, hotels and other public buildings.
Sprinklers have been in use in the United States since 1874, and were used in factory applications where fires at the turn of the century were often catastrophic in terms of both human and property losses. In the US, sprinklers are today required in all new high rise and underground buildings generally 75 feet (23 m) above or below fire department access, where the ability of firefighters to provide adequate hose streams to fires is limited. Sprinklers may also be required in hazardous storage spaces by building codes, or may be required by insurance companies where liability due to potential property losses or business interruptions can be reduced by adequate automatic fire protection. Building codes in the United States for places of assembly, generally over 100 persons, and places with overnight sleeping accommodation such as hotels, nursing homes, dormitories, and hospitals usually require sprinklers. A newer, special class of fire sprinklers, ESFR sprinklers, has been developed to fight, and subsequently suppress high challenge type fires.
Each sprinkler head is held closed independently by heat-sensitive seals. These seals prevent water flow until a design temperature is exceeded at the individual sprinkler heads.
Each sprinkler activates independently when the predetermined heat level is reached. The design intention is to limit the total number of sprinklers that operate, thereby providing the maximum water supply available from the water source to the point of fire origin.
Typical "wet" systems are simple and passive. They have water already pressurized in the pipes held back by the sprinkler head. These systems require no manual controls to activate, so long as adequate water supplies are provided.
Specialty systems called "dry" systems, designed for unheated spaces, have a low "maintenance" air pressure in the pipes. Water is fed into the system when the sprinkler "fuses" allowing the maintenance air pressure to reach the minimum pressure point. "Pre-action" systems are highly specialized for locations where accidental activation is unacceptable such as museums with rare art works, manuscripts, or books. Pre-action valves are connected to fire alarm initiating devices such as smoke detectors or heat detectors and virtually eliminate the possibility of accidental water flow.
"Deluge" systems are "pre-action" systems that have open sprinklers, i.e. the fusible link is removed, so that every sprinkler served by the system will discharge water. This ensures a large and simultaneous application of water over the entire hazard. These systems are used for special hazards where rapid fire spread is a concern.
Other specialty systems may have foam instead of water suppression agents for fire protection in occupancies with flammable liquids, such as airport hangars. "Clean agent" gaseous systems, such as Argon/CO2/Nitrogen mixtures can be used in very small spaces where water cannot be used for suppression.
A sprinkler activation will do less damage than a fire department hose, as the fire department's hose streams provide around 250 US gallons per minute (15 L/s) whereas an activated sprinkler head generally discharges around 23 US gallons per minute (1.5 L/s).
In 2006, cost of sprinkler systems run from US$2 - $5 per square foot ($50/m²), depending on type and location, however specialty systems may cost as much as $10/square foot ($100/m²). Systems can be installed during construction or retrofitted. Some communities have laws requiring residential sprinkler systems, where large municipal hydrant water supplies ("fire flows") are not available. Nationwide in the United States, one and two-family homes generally do not require fire sprinkler systems, although the overwhelming loss of life due to fires occurs in these spaces. Residential sprinkler systems are relatively inexpensive (about the same per square foot as carpeting or floor tiling), but require larger water supply piping than is normally installed in homes, so retrofitting is usually cost prohibitive.
According to the National Fire Protection Association (NFPA), fires in hotels with sprinklers averaged 78% less damage than fires in hotels without them (1983-1987). The NFPA says the average loss per fire in buildings with sprinklers was $2,300, compared to an average loss of $10,300 in unsprinklered buildings. The NFPA adds that there is no record of a fatality in a fully sprinklered building outside the point of fire origin. However, in a purely economic comparison, this is not a complete picture; the total costs of fitting,