Dry sprinkler system

Define areas and buildings to use wet and dry sprinkler systems, foam systems, location of hand and hose fire extinguishers, fire carts, fire engines. 

Dry sprinkler system consists of sprinkler pipework pressurised with air. When a sprinkler head ruptures water enters the system. 

Like the dry sprinkler system, the deluge system has several disadvantages ... 

Dry pipe sprinkler system a system filled with nitrogen or air under pressure. When the sprinkler is opened by heat, the system is depressurized, allowing water to flow into the system and out the open sprinklers. 

Rainwater leaked into a room where hundreds of drums of dry swimming pool chemicals were stored, causing an explosion. The explosion and resulting fire set off the sprinkler system that soaked the remaining drums. The fire, explosions and chlorine releases lasted three days. Over 25,000 people were evacuated, and 275 people went to the hospital with skin bums and respiratory problems. 

There are four basic types of sprinkler systems wet pipes, dry pipes, pre-action, and deluge. These are described in the following sections. 

The principal difference between a pre-action system and a standard dry pipe system is that in the pre-action system, the water supply valve is actuated independently of the opening of the sprinklers. The water supply valve is opened by the operation of an automatic fire detection system, which immediately allows water to enter the overhead piping. Then, when the fire generates enough heat to fuse the sprinkler head, water is immediately discharged on the fire as with a wet pipe system. This system reduces the inherent time lag of a dry pipe system, but can still be used in unheated areas. An example of a pre-action system is shown in Figure 7-26. 

The availability of pre-action systems depends heavily upon the availability of the associated independent detection system. To compensate for this, systems should be designed so that the valve can be opened manually, both locally and at a constantly attended location. In addition, because of the complex mechanical valve arrangement, pre-action systems are less reliable than wet and dry pipe sprinkler systems. 

Small wet pipe systems can be protected by an antifreeze solution. The extent of the system should be limited to 20 sprinkler heads or less. For systems over 20 sprinkler heads, a dry pipe system should be used. 

Sprinkler The test should be made at no less than 200 psi (1,379 kPa) for 2 hours or 50 psi (345 kPa) above static pressure, where static pressure is in excess of 150 psi (1,034 kPa) for 2 hours. Additionally, dry pipe systems require an air test after the hydrostatic test. The air test is at an initial air pressure of 40 psig (276 kPa) with loss not exceeding 1.5 psig (10.4 kPa) in 24 hours. 13... 

The dry pipe system was probably too slow in operation and did not provide a density sufficient to extinguish the fire. The new system was designed for a sprinkler density of 0.6 gpm/ ft (24 Ipm/m ) which was more than three times the original design density. 

Dry-pipe Sprinkler Systems A fire protection sprinkler system that has air instead of water under pressure in its piping dry systems are often installed in areas subject to freezing. 

Dry-pipe Valve A valve in a dry-pipe sprinkler system designed so that moderate air pressure will hold back a much greater water pressure. 

Fire protection is another critical safety concern. Automatic fire detectors are located throughout the plant. Sprinkler systems supplied from a large storage tank come on automatically in the event of a fire in the unloading and unpack areas. In other areas, dry chemical systems are deployed. Halon systems protect the control room and power supply room. 

There are two different types of water sprinkler systems, wet-pipe and dry-pipe. The lines leading to the sprinkler heads are full of water in a wet-pipe system so that water will be discharged immediately from an open sprinkler head, while in a dry-pipe system, the lines are full of air under pressure instead of water. This latter type of unit should be used where the temperature is not maintained above freezing at aU times. Both types of systems include a main control valve which is designed not only to supply water to the sprinkler heads but also to provide a mechanism to cause an alarm to sound. The valves also usually provide a visual indication of whether they are open or closed. Except during maintenance, they should be in the open position. There are a number of design features for these valves which are beyond the scope of this document, except to note that some are intended to avoid false alarms due to surges or variations in the water supply pressure to the system. 

A variation of the dry-pipe system is the deluge system. The sprinkler heads are continuously open and water is prevented from entering the system by a deluge valve. When a fire is detected the valve to the water supply opens and water flows into the system and out of aU the sprinkler heads. This not only wets the immediate area of a small fire, but the entire area to which the fire may spread. This type of system is usually chosen when the contents of the space are unusually hazardous. A variation on this system is the pre-action system in which the sprinkler heads are not open, but when a fire is detected the deluge valve opens and water is supplied to the sprinkler heads. The water entering the system causes an alarm to be sounded. When the heat causes the sprinkler heads to fuse, or open, water is discharged onto the fire. 

Sprinkler Systems, Installation of, National Fire Protection Association, Quincy, MA Dry Chemical Extinguishing Systems, National Fire Protection Association, Qiuncy,... 

Dry-Pipe Systems A dry-pipe system contains air or nitrogen under pressure at all times. A valve separates water supplies from the dry pipes. An open head will reduce the pressure in the gas-charged pipes and allow the valve to open, releasing water to the open sprinkler head and the fire. Ehy-pipe systems are suitable for areas subject to freezing. Compared to wet-pipe systems, dry-pipe systems respond slower to a demand for water at a sprinkler head and more heads are likely to open in a fire. Special featores prevent inadvertent operation of the water valve. 

Preaction Systems This is a special fonii of dry-pipe system. The piping may or may notbe under pressure. There are sensors in protected areas besides sensors at each sprinkler head. The special sensors detect a fire and open a valve to fiU the pipe with water. The special sensors operate before those in the sprinkler heads. This design reduces the delay found in a dry-pipe system. 

Com bi ned Systems These systems combine features of a dry-pipe system and a preaction system. Pipes are filled with air under pressure. Supplementary sensors open a water valve and air exhaust ports. This allows the piping to fill completely with water before the sprinklers open. 

In addition to the sprinkler system adequacy, is additional fire protection, such as an automatic dry chemical extinguishing system or a other system, warranted Is an explosion suppression system warranted ... 

Four types of sprinkler systems are available wet-pipe, dry-pipe, alternate and pre-action. A wet-pipe system can only be used in premises not subject to frost or ambient temperatures above 70 C. A dry-pipe system is only suitable in premises subject to continuous temperatures below 0 C or above 70 C. An alternate system which enables either wet or dry operation to be selected is suitable in premises subject to freezing during cold weather. Finally a pre-action system, which is a system with a separate heat or smoke detector that allows water into the sprinkler pipework before the first head operates, should only be used where none of the others is suitable. 

A variety of valves are required on a sprinkler system. There must be a main stop valve which on a wet system must be locked open, conveniently placed and fitted with an approved sign. Downstream of this is an alarm valve which opens when a demand is put on the system and also provides a flow to actuate the alarm. Other valves include a drain valve which allows the system to be drained and tests to be carried out on the system and a test valve which simulates the operation of a sprinkler head and enables the operation of the alarm valve and the alarm to be tested. Dry systems and alternate wet/dry systems require further valves. The principal valves in the control units of various types of sprinkler installation are summarised in Table 25.8. 

---