Fire sprinkler system
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A Fire sprinkler system is an active fire protection measure, consisting of a water supply, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected. Although historically only used in factories and large commercial buildings, home and small building systems are now available at a relatively cost-effective price.
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[edit] History
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. [1]
Henry S. Parmalee of New Haven, Connecticut is considered the inventor of the first 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. Frederick Grinnell improved Parmalee's design and in 1881 patented the automatic sprinkler that bears his name. He continued to improve the device and in 1890 invented the glass disc sprinkler, essentially the same as that in use today. [2]
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.
[edit] Usage
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.
[edit] Operation
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.
A sprinkler activation will do less damage than a fire department hose, as the fire department's hose streams provide around 900 liters per minute (250 US gallons/min.) whereas an activated sprinkler head generally discharges around 90 liters per minute (23 US gallons/min.). In addition, the sprinkler will activate immediately; whereas a fire appliance takes an average of eight minutes to reach an incident. This delay can result in substantial damage from the fire before the appliance arrives and will the fire will be much larger; requiring much more water to extinguish.
[edit] Types
[edit] Wet pipe systems
Wet pipe sprinkler systems are installed more often than all other types by a wide margin. They also have the highest reliability, as they are simple, with the only operating component being the automatic sprinkler. A water supply provides pressure to the piping, and all of the piping is filled with water adjacent to the sprinklers. The water is held back by the automatic sprinklers.
Operation - When one or more of the automatic sprinklers is exposed to sufficient heat, it operates, allowing water flow from that sprinkler. Each sprinkler operates individually.
[edit] Dry pipe systems
Dry pipe systems can only be used (by regulation) in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, rendering the system inoperable. Dry pipe systems are most often used in unheated buildings, in outside canopies attached to heated buildings (in which a wet pipe system would be provided), or in refrigerated coolers. Dry pipe systems are the second most common sprinkler system type.
Water is not present in the piping until the system operates. The piping is pressurized with air, at a "maintenance" pressure which is relatively low compared with the water supply pressure. To prevent the larger water supply pressure from forcing water into the piping, the design of the dry pipe valve (a specialized type of check valve) intentionally includes a larger valve clapper area exposed to the maintenance air pressure, as compared to the water pressure.
Operation - When one or more of the automatic sprinklers is exposed to sufficient heat, it operates, allowing the maintenance air to vent from that sprinkler. Each sprinkler operates individually. As the air pressure in the piping drops, the pressure differential across the dry pipe valve changes, allowing water to enter the piping system. Water flow from sprinklers needed to control the fire is delayed until the air is vented from the sprinklers. For this reason, dry pipe systems are usually not as effective as wet pipe systems in fire control during the initial stages of the fire.
[edit] Deluge systems
"Deluge" systems are systems that have open sprinklers, i.e. the heat sensing operating element is removed during installation, so that all sprinklers connected to the water piping system are open. 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.
Water is not present in the piping until the system operates. Because the sprinkler orifices are open, the piping is at ambient air pressure. To prevent the water supply pressure from forcing water into the piping, a deluge valve is used in the water supply connection, which is a mechanically latched valve. It is a non-resetting valve, and stays open once tripped.
Because the heat sensing elements present in the automatic sprinklers have been removed (resulting in open sprinklers), the deluge valve must be opened as signaled by a specialized fire alarm system. The type of fire alarm initiating device is selected mainly based on the hazard (e.g., smoke detectors, heat detectors, or optical flame detection). The initiation device signals the fire alarm panel, which in turn signals the deluge valve to open. Activation can also be manual, depending on the system goals. Manual activation is usually via an electric or pneumatic fire alarm pull station, which signals the fire alarm panel, which in turn signals the deluge valve to open.
Operation - Activation of a fire alarm initiating device, or a manual pull station, signals the fire alarm panel, which in turn signals the deluge valve to open, allowing water to enter the piping system. Water flows from all sprinklers simultaneously.
[edit] Pre-Action Systems
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.
Pre-action systems are hybrids of wet, dry, and deluge systems, depending on the exact system goal. There are two sub-types of pre-action systems: single interlock, and double interlock. The operation of single interlock systems are similar to dry systems except that these systems require that a “preceding” and supervised event (typically the activation of a heat or smoke detector) takes place prior to the “action” of water introduction into the system’s piping due to opening of the pre-action valve (which is a mechanically latched valve). Once the fire is detected by the fire alarm system, the system is essentially converted from a dry system into a wet system. Or, if an automatic sprinkler operated prior to the fire being detected by the fire alarm system, water will be allowed into the piping, and will discharge water from the sprinkler.
The operation of double interlock systems are similar to deluge systems except that automatic sprinklers are used. These systems require that both a “preceding” and supervised event (typically the activation of a heat or smoke detector), and an automatic sprinkler activation take place prior to the “action” of water introduction into the system’s piping. There is also a little used variation known as Non-Interlock.
[edit] Foam water sprinkler systems
A foam water fire sprinkler system is a special application system, discharging a mixture of water and low expansion foam concentrate, resulting in a foam spray from the sprinkler. These systems are usually used with special hazards occupancies associated with high challenge fires, such as flammable liquids, and airport hangars. Operation is as decribed above, depending on the system type into which the foam is injected.
[edit] Water spray
"Water spray" systems are operationally identical to a deluge systm, but the piping and discharge nozzle spray patterns are designed to protect a uniquely configured hazard, usually being three dimensional components or equipment (i.e., as oppooed to a deluge system, which is designed to cover the horizontal floor area of a room). The nozzles used may not be listed fire sprinklers, and are usually selected for a specific spray pattern to conform to the three dimensional nature of the hazard (e.g., typical spray patterns being oval, fan, full circle, narrow jet). Examples of hazards protected by water spray systems are electrical transformers containing a flammable liquid as a cooling oil, or tanks containing a flammble gas such as hydrogen.
[edit] Design
| Temperature | Colour of liquid
inside bulb |
|
|---|---|---|
| °C | °F | |
| 57 | 135 | Orange |
| 68 | 155 | Red |
| 79 | 174 | Yellow |
| 93 | 200 | Green |
| 141 | 286 | Blue |
| 182 | 360 | Mauve |
| 227 260 |
440 500 |
Black |
This chart from the
New Zealand fire
safety standards
indicates the colour
of the bulb and the
respective operating
temperature.
Most sprinkler systems installed today are designed using an area and density approach. First the building use and building contents are analyzed to determine the level of fire hazard. Usually buildings are classified as light hazard, ordinary hazard group 1, ordinary hazard group 2, extra hazard group 1, or extra hazard group 2. After determining the hazard classification, a design area and density can be determined by referencing tables in the National Fire Protection Association (NFPA) handbooks. The design area is a theoretical area of the building representing the worst case area where a fire could burn. The design density is a measurement of how much water per square foot of floor area should be applied to the design area. For example, in an office building classified as light hazard, a typical design area would be 1500 square feet and the density would be 0.1 gallons per minute per square foot or a minimum of 150 gallons per minute applied to the 1500 square foot design area. Another example would be a warehouse classified as ordinary hazard group 2 where a typical design area would be 1500 square feet and the density would be 0.2 gallons per minute per square foot or a minimum of 300 gallons per minute applied to the 1500 square foot design area.
After the design area and density have been determined, calculations are performed to prove that the system can deliver the required amount of water to the required design area. These calculations account for all of the pressure that is lost or gained between the water supply source and the sprinklers that would operate in the design area. This includes pressure that is lost due to friction inside the piping, pressure that is lost or gained due to elevation differences between the source and the discharging sprinklers, and sometimes momentum pressure from water velocity inside the piping is also calculated. Typically these calculations are performed using computer software but before the advent of computer systems these sometimes complicated calculations were performed by hand. This skill of calculating sprinkler systems by hand is still required training for a sprinkler system design Technologist who seeks senior level certification from engineering certification organizations like the National Institute for Certification in Engineering Technologies (NICET).
Sprinkler systems in residential structures are becoming more common as the cost of such systems becomes more practical and the benefits become more obvious. Residential sprinkler systems usually fall under a residential classification separate from the commercial classifications mentioned above. A commercial sprinkler system is designed to protect the structure and the occupants from a fire. Most residential sprinkler systems are primarily designed to suppress a fire in such a way to allow for the safe escape of the building occupants. While these systems will often also protect the structure from major fire damage, this is a secondary consideration. In residential structures sprinklers are often omitted from closets, bathrooms, balconies, and attics because a fire in these areas would not usually impact the occupant's escape route.
If water damage or water volume is of particular concern, a technique called Water Mist Fire Suppression may be an alternative. This technology has been under development for over 50 years. It hasn't entered general use, but is gaining some acceptance on ships and in a few residential applications. Mist suppression systems work by lowering the temperature of a burning area through evaporation rather than "soaking". As such, they may be designed to only to slow the spread of a fire and not extinguising it. Some tests, that may or may not be biased, showed the cost of resulting fire and water damage with such a system installed to be dramatically less that conventional sprinkler systems.[1]
[edit] Costs
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, and the costs arising from non-fire triggered release must be factored.
The NFPA states that it "has no record of a fire killing more than two people in a completely sprinklered building where a sprinkler system was properly operating, except in an explosion or flash fire or where industrial fire brigade members or employees were killed during fire suppression operations."
The world's largest fire sprinkler manufacturer is the SimplexGrinnell division of Tyco International, other manufacturers / suppliers include The Viking Corporation, NNI Inc, P.u.P. Feuerschutz und Anlagenbau GmbH and Reliable Sprinkler Company.
[edit] References
- ^ SPRINKLER HISTORY Merit Sprinkler Company
- ^ Casey Cavanaugh Grant, PE The Birth of NFPANFPA1996
[edit] See also
- Active fire protection
- Passive fire protection
- Fire protection
- Fire protection engineering
- Architectural engineering
- Bounding
[edit] External links
