User Manual

33
Siemens Switzerland Ltd
Building Technologies Division
Local conditions such as temperature and building usage determine which type of sprinkler system should be
implemented.
Wet-pipe systems Wet-pipe systems should only be installed in situations where the water in the
piping network is not subject to freezing or overheating (+95 °C) during the year.
This includes most applications in heated buildings. Such systems are
permanently filled with water, which is maintained under pressure so that in case
of fire the water can be immediately discharged from the sprinklers.
Dry-pipe systems Dry-pipe systems should be installed in situations where there is a risk of frost.
Typical applications include unheated buildings, underground car parks, loading
bays and commercial freezers.
The pipework is similar to that used in wet-pipe systems; however, the
pressurized water is retained behind the dry-pipe alarm valve. The piping on the
sprinkler side of this valve is filled with air or an inert gas under pressure. In the
case of fire, the air must first escape before the water can reach the sprinklers,
leading to an inevitable delay: this is one of the disadvantages of this type of
system.
4.3.2. 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, computer rooms, archives and document safes.
The gases are stored in pressure tanks:
• The non-liquefiable inert gases Ar, N
2
• In high-pressure systems CO
and gas mixtures are stored in gas cylinders at pressures of 200 to
300 bar.
2
• Chemical gases are stored in gas cylinders, pressurized with nitrogen which acts as a propellant. The
industry norm storage pressure is 42 bar in Europe (and 25 bar in the USA).
(which does liquefy under pressure) is stored in gas cylinders at 56 bar; in
low-pressure systems it is stored in large cooled containers.
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 formation
phase. However, to prevent human casualties, an alarm must first be sounded to warn people of the imminent
flooding of the area. The gas will only be released after a predefined delay has given people sufficient time to
evacuate the area.
When the system is actuated, the cylinder valves of high-pressure systems (or the container valves of low-pressure
systems) will be opened. Doors and other openings are closed automatically and any other air-handling
equipment (e.g. ventilation systems and smoke dampers) are controlled to ensure that the area is sealed off.
However, the inrush of the extinguishing gas into a closed room will automatically increase the pressure within
the room. To prevent damage occurring, overpressure relief dampers mechanisms temporarily open, before re-
closing again automatically.
The extinguishing gas is guided through a network of piping to nozzles that are evenly distributed on the ceiling.
The gas quickly fills the room and a homogenous concentration is built up throughout the room. To completely
extinguish the fire, this concentration must be maintained over a sufficiently long period of time.