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.
All of the piping is filled with water. Until sufficient heat
is applied, causing one or more sprinklers to fuse (open), the
automatic sprinklers prevent the water from being discharged.
Operation
- When an automatic sprinkler is exposed to sufficient heat, the
heat sensitive element (fusible link) releases, allowing water
to flow from that sprinkler. Sprinklers are manufactured to react
to a specific range of temperatures. Only sprinklers subjected
to a temperature at or above their specific temperature rating
will operate.
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Dry
pipe systems
Dry pipe systems can only be used (by regulation[3]) 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.
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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.
A
deluge system may be required in a risk area where fire may be
expected to spread quicker than the progressive operation of normal
sprinkler heads.
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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.
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Carbon
Dioxide Systems
Carbon
dioxide is a clean, non-corrosive, non-flammable gas which extinguishes
fire by diluting flammable mixtures of air and gas or vapor to
proportions below their flammable or explosive limits. It is especially
valuable where other extinguishing mediums might damage stock
or equipment.
Suitable
for electrical room, transformer room, boiler room, etc…
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Foam
Systems
There
are a variety of effective fire fighting foams in use. These are
made from liquid concentrates and are referred to as mechanical
or air foam.
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Clean
Agent Gas Systems
FM
200, Inergen, and Novec 1230 are all Clean Agent Gas Systems that
are a replacement to Halon 1301. Each of these gas systems is
a clean, non-corrosive gas, which is designed to extinguish fire.
All are especially valuable where other extinguishing medias might
damage stock or valuable equipment. These systems are used most
often in computer, electrical, and telecommunication equipment
rooms. A description of each and how they differ is as follows:
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FM
200 Systems
Extinguishes Class A, B, and C fires by interrupting the chemical
chain reaction. It also absorbs heat, thus accelerating the suppression
process. This gas is safe to use in occupied spaces at concentrations
up to 9% by volume. FM 200 will not deplete stratospheric ozone
and it has a relatively short atmospheric life time of 31-42 years.
Suitable
for a central computer room or a room which stores important document
or items etc …
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Novec
1230 Systems
Novec 1230 fluid works as a gas yet it is a liquid at room temperature.
Novec is used to extinguish Class A, B and C fires via its cooling
effects. This agent extinguishes fires at concentrations of 4-6%
by volume and thus it offers the largest safety margin of any
chemical clean agents for occupied spaces.
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Inergen
Systems
Extinguishers Class A, B and C fires by removing enough oxygen
from the air to break the fire chain, yet still allowing people
to breathe comfortably. For Class A and B fires the speeds of
extinguishment have occurred in as little as 22 and 17 seconds
respectively. Inergen is completely environmentally friendly.
It is composed of naturally occurring gases already found in the
air we breathe. It has zero ozone depletion, global warming, and
atmospheric lifetime potential.
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Water
Mist Systems
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 slow the spread of a fire and not extinguish 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 than conventional sprinkler systems.
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