HOW FIRE SPRINKLERS OPERATE
The easiest way to understand the operation of a fire sprinkler is to think of a
fire sprinklers as a "heat-sensitive" plug.
Contrary to what is commonly
portrayed in movies and on television, normal fire sprinklers operate only
when heated to a designated temperature. This means that if you have a fire
in a room, only the head(s) that get hot enough to open will open and spray
water (statistically, that number is between 1 & 2). Smoke (and attractive
people) do not actually cause regular fire sprinklers to operate.
The typical options for Fire Sprinkler System types are:
1. Wet-pipe system (Wet System)
Wet systems are the most common type of fire sprinkler system and are the simplest. Wet systems have
water-filled pipe and release water as soon as sprinkler heads operate. (Wet systems are restricted
to use only in areas where the temperature is maintained above 40o
2. Dry-pipe system (Dry System)
Dry systems are used where the area
protected by the sprinkler system is subject to freezing. Dry systems have a
system control valve that is held closed by compressed air within the system
piping. When a head breaks, the air is released, and the valve opens and
allows water to enter the piping and discharge onto the fire. Dry systems
understandably take longer to respond to a fire than a wet system, so
different design criteria are used for dry systems to account for the delayed
3. Pre-Action system (Preaction System)
Like dry systems, preaction systems
normally have only pressurized air in the pipe, but unlike a dry system,
merely releasing the air pressure will not allow water into the pipe.
Preaction systems use an electric solenoid-operated "preaction valve" to hold
back water. The preaction valve is controlled by a special fire alarm panel,
called a releasing panel, which can be configured to release water after
receiving either one or multiple signals (whether or not sprinkler heads are
broken). Common methods of fire detection used for releasing a preaction
valve are: monitoring system piping for air pressure loss (supervisory air),
Fire Detectors (Spot-type Heat; Linear Heat; Smoke; and Flame), and pilot
sprinklers. Some examples of areas where preaction systems make sense are:
Rooms where the system piping is likely to be subjected to mechanical damage
(i.e.: palletized storage racking), or where the contents are extremely
valuable and fire fighting with water is a last resort (i.e.: server rooms,
clean rooms, telecom switch rooms), or rooms where a dry system would be
appropriate because of low temperature, but a delayed response (from
exhausting air) is unacceptable (i.e.: warehouses with contents that would
develop high-challenge fires).
4. Deluge systems
- Deluge systems are systems with open nozzles that are
intended to spray every part of a structure in the event of a release.
Deluge systems are released by means of a releasing panel as a preaction
system is (but supervisory air is not an option due to the open nozzles).
Deluge systems are used to protect buildings or structures that will develop
fast, high-challenge fires, such as Petroleum Storage Tanks, Fuel Tanker
Loading Racks, Cooling Towers, etc.
5. Anti-freeze system (Antifreeze system)
- Antifreeze systems are wet
systems with special control valves installed that permit filling the piping
with a non-freezing solution. Antifreeze systems are frequently used to
protect small areas which are subject to freezing, within buildings that are
otherwise protected with wet systems (such as attics, garages, or exterior
canopies). Sometimes large antifreeze systems are installed to protect
commercial cold storage buildings, but such installations are expensive and