DESCRIPTION AND APPLICATION

The inert gas Fire suppression systems are clean agent systems; the norms regulating this extinguisher are the NFPA 2001, the ISO 14520, the UL 2127 and the UNI 10877/14. They do not operate chemically on the flame like Halon 1301, but they reduce the temperature of the flame at a level at which combustion cannot be produced.

The gases used are normally present in the atmosphere, ARGON and AZOTE, and are colourless and non corrosive. Moreover they are environmentally friendly as no residues are produced by their combustion.

The functioning is based on the principle of total flooding; the great advantage is therefore that there is no need to worry about the location neither of the material to be protected nor of its shape because homogeneous conditions in all the room are created. As a result of the descending blend air-extinguishing agent, it is important to indicate the maximum height at which objects to be protected is placed.

Another essential parameter is the calculation of the total volume to be protected in order to determine the quantity of gas to be used. The specifications of the rooms to be protected are essential for a valid planning of the system and in fact the NFPA norm requires the Door Fan Integrity Test: the closure of all the openings with automatic fittings and the immediate stop of any ventilation system are fundamental for a good functioning of the system.

In particular confined places where various openings more or less sealed are present and from where the extinguishing gas can leak out, the method of double release is used. After a first release, a second one follows so as to keep the gas concentration at the parameters required.

As for the concentration limits and people exposure to the inert gas, reference is made to the USA Environmental Protection Agency and to the Reinhardt Protocol. These are the following:

NOAEL - No Observable Adverse Effect Level (maximum value of concentration of the extinguishing agent
without collateral effects);

LOAEL - Lowest Observable Adverse Effect Level (minimum value of concentration of the extinguishing agent at
which collateral effects are noticed)


Table A - Max. Concentration levels



It is therefore clear that in spaces normally occupied by personnel, the oxygen concentration cannot be reduced below 12 % if human presence in the rooms where gas is released for 5 minutes is desired.

The proliferation of clean agent suppression systems of the Halocarbons and inert gas type has caused the insertion of a new Protocol in the standard NFPA 2001 aimed to check the toxic compatibility and called PBPK- Physiologically Based Pharmacokinetic model which takes into account the maximum acceptance of the agent in the blood and the time to reach it.

The inert gas suppression system is made of pressurised storage containers (cylinders) connected through valves to a pipe network to send it to destination (collector and distribution pipes). At the end of it, the gas is released through engineered nozzles into the rooms or objects to be protected.