Gas Fire Suppression Systems
Electronic and paper data are valuable commodities and it is often necessary to protect them from fire. It is also desirable to protect expensive electronic and computer equipment, thus water is not an acceptable fire extinguishent medium.
Halon and FM 200 have traditionally been used as fire extinguishent gasses but have been phased out due to their ozone depleting effects.
Argonite and Inergen are now replacing these gasses, as safe and non environmentally damaging alternatives.
Argonite is a mixture of Argon and Nitrogen stored as gas, usually in 80 litre cylinders @ 200 bar (2940 psi) Each 80 litre cylinder generates 16 m3 of gas on release to atmosphere over 1 minute, giving an average release rate of 0.266 m3 /s per cylinder, however this is non-linear.
The peak discharge rate is 21.4 Kg/sec or 0.47 m 3 /s falling to zero over 60 seconds, therefore we work on an average discharge rate of 0.35 m3/s for valve sizing. Argonite reduces the oxygen level from a typical value of 20.9% down to 12.5% thus extinguishing the fire without leaving damaging residues. Argonite is electrically non-conductive and is safely breathable for staff during evacuation.
This is a mixture of 40% Argon, 52% nitrogen and 8% carbon dioxide - the latter aids breathing for fire fighters. Like Argonite it does not deplete the ozone layer. The discharge of Inergen reduces the oxygen content in a room to approximately 12.5%, while increasing the carbon dioxide content to about 3%.
Most fires are extinguished when the oxygen content falls below 15%. Inergen is available in 27, 40, 67 and 80 litre cylinders at 200 bar pressure and its behaviour is similar to Argonite.
Inergen gas - average release rate per second
|Standard ISO/US FS 209D||Average Air Flow Velocity||Air changes/hour|
|27||5.8 m3||0.096 m3/s|
|40||12.2 m3||0.203 m3/s|
|67||14.4 m3||0.240 m3/s|
|80||17.2 m3||0.286 m3/s|
It is suggested that 25% be added to these flow rates to give a safety margin when sizing a valve in view of the non linear rate of release.
Carbon dioxide (only to be used in areas where no personnel are present)
Carbon dioxide can only be used in non occupied areas.
Standard cylinder (K size) contains 34 Kg. of liquefied gas.
The evaporation rate is 0.534 m3/Kg.
Therefore one cylinder will release 18.156 m3 of gas at atmospheric pressure.
Buildings can typically stand pressures of between 100 and 500 Pa, depending on the method of construction. However room pressures should be limited to 250 Pa unless the architect can guarantee the building is capable of withstanding a higher pressure.
Where the building safe working pressure is limited to 50 Pa or less, use LF stabilisers.
For safe working pressures of between 50 and 100 Pa, select Type T valves.
Where building pressures of greater than 100 Pa are allowed, select a suitable X or Z Type valve from our sizing charts, based upon the calculated flow rate of gas.
In all cases allow for any pressure loss through ductwork and weather louvres which should be added to the pressure setting of the valve to give the overall resistance.