User Manual

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Water mist systems
An emerging fire-sprinkler technology which shows great
promise particularly for sensitive applications is the use of
water mist. A fine water vapor is generated by delivering
water to the specially designed sprinkler heads at very
high pressures. This maximizes the cooling effect of the
water, enabling fires to be extinguished with minimal
amounts of water. Experimental tests have shown that
many room fires can be controlled with a very small
amount of water. This type of system is usually activated
by control signals from the fire detection system, in
response to alarm signals from the connected fire
detection devices. The disadvantages of this type of
system compared with traditional wet-pipe systems are
that they are somewhat more expensive to install and the
maintenance costs are also higher.
5.3.2 Gas extinguishing systems
The main application area for gas extinguishing systems
is the protection of closed rooms. They are particularly
suitable for rooms that contain sensitive objects or
equipment where water cannot be used. These typically
include all types of electrical equipment and computer
rooms.
The gases are stored in pressurized cylinders:
 The non-liquefiable inert gases N
2, Ar and gas
mixtures are stored in gas cylinders at a pressure
of 300 bar.
 In high-pressure systems CO2 (which liquefies under
pressure) is stored in gas cylinders at 56 bar; in low-
pressure systems it is stored in large cooled
containers.
 Clean agents such as HFC227ea and Novec 1230 fluid
are stored in gas cylinders pressurized with nitrogen,
which acts as a propellant. The industry’s most
common storage pressures are 25 bar (particularly in
the USA) and 42 bar, which allows for higher flow
rates, smaller pipe diameters and longer pipe runs.
Extinguishing is controlled either manually or preferably
automatically by means of a fire detection system. Only a
quick, faultless actuation prevents consequential damage,
as a fire should be extinguished during its incipient phase.
However, to prevent human casualties, an alarm must
first be sounded to warn people of the imminent flooding
of the area. The extinguishing gas will only be released
after a predefined delay has given people sufficient time
to evacuate the area. The gas will then be released and a
homogenous concentration is quickly built up throughout
the room. To completely extinguish the fire, this
concentration must be maintained over a sufficiently long
period of time.
Standard extinguishing nozzle
5.3.3 Gas/water-combined systems
An alternative to the pure gas systems can be provided by
proprietary systems using a combination of gas and water
mist. Releasing additional N
2 gas into a closed room,
where an embryonic fire has been detected, effectively
reduces the oxygen concentration in the room and
extinguishes the fire, while the water mist cools the
combustible material and prevents re-ignition. The fine
water mist also serves to provide a smoke scrubbing
function, which reduces the health hazard for people
entering the room following an extinguishing event:
smoke inhalation is the primary cause of death for victims
of indoor fires.
Such systems provide an excellent solution for archives,
as they combine the following major advantages:
 They ensure that incipient fires are extinguished
rapidly and reliably
 They prevent re-ignition
 They create no irreversible damage to the documents
and drawings stored in the archive.
5.4 Manual extinguishing infrastructure
5.4.1 Fire extinguishers
[1]
Fire extinguishers are mobile or portable manual devices
designed for preventing incipient stage fires from getting
out of control. The extinguishing agent is expelled under
pressure. In some types of extinguisher the agent is kept
under constant pressure, while in others the pressure is
generated by releasing a propellant gas at the time that
the extinguisher is activated.
National fire codes (e.g. BGR 133) specify the type, size
and quantity of extinguishers required with regard to the
floor area and danger level of each location. It is
important to provide an adequate number of fire
extinguishers, which should be installed throughout the
building. They should be mounted where they are clearly
visible, easily accessible and at a convenient height.
Typically the extinguisher handle should be between 0.8
and 1.2 m from the floor. The weight of the extinguishers
is also a factor that should be taken into consideration
during the selection process: the 6 liter extinguishers
are recommended.
Extinguishing agents include water, foam, carbon dioxide
and powder. These substances function in different ways
and are suitable for different types of fires. The table
below shows which type of extinguisher should be
provided in the various college or university building
areas.