Last edited 01 Oct 2019

Clean agent

Clean agents (clean fire extinguishing agents or gaseous fire suppressants) take the form of inert gases that were developed as an environmentally acceptable alternative to halon which is banned in the UK. The gaseous fire suppressant is stored as a pressurised liquid which when discharged into the air turns immediately to gas and can smother a fire. However, some types also discharge as a rapidly evaporating liquid.

These fire suppressants are typically non-corrosive, do not usually damage delicate equipment that is away from the fire and do not usually leave a residue. They work by blocking the combustion reaction while it is occurring.

For these reasons, clean agents are effective on electrical fires; they offer a further benefit in that, unlike water and other liquids, they are formulated to not conduct electricity back to the operator. They are therefore used in wide-bodied commercial aircraft, pharmaceutical and industrial plants, computer rooms, clean rooms, switch rooms, data storage, telecoms areas and art storage areas, to name but a few.

A clean agent suppressant system typically consists of the agent, the container it is stored in, agent release valves, fire detectors, fire detection system (wiring control panel, actuation signalling) and the means to convey the agent to the fire – the piping and dispersion nozzles. Also possible, although less common, is delivering the agent using a solid propellant gas generator that produces either inert or chemically active gas.

Clean agent fire suppressants may be effective in fighting the following European fire classifications:

Class A: Combustible materials (wood, paper, fabric, most kinds of refuse);
Class B: Flammable liquids;
Class C: Flammable gases.

Clean agent fire suppressants can also come in traditional hand-held portable cylinder fire extinguishers, with an activation trigger and nozzle. Or, they may be ceiling-mounted circular discs of 4-10kg capacities with automatic fire detection and activation. Being ceiling mounted they are designed to have a better reach than normal fire extinguishers and are useful in areas where the chances of early fire detection are low. This includes areas where there is little human traffic flow e.g in factories with large storage areas, server rooms and areas such as high chemical stacks that are beyond the range of normal fire extinguishers. A downside is that the red ‘bulb-shaped’ containers can look unsightly although this may not be considered problematic in an industrial setting.

[edit] Halon

In the past, many systems used halon as the base extinguishing agent, considered then as being an ‘environment friendly’ fire extinguishing chemical which produced a halogenated effect. In particular, a variant called HCFC 123 used in some systems was introduced in the 1990s to replace ozone-depleting agents such as Halon 1211 and BCFs.

HCFC 123 was at one time regarded as one of the ‘cleanest’ and ‘most powerful’ extinguishing agents available. According to Gov.UK. HCFC 123 (C2HF3Cl2 Dichlorotrifluoroethane) has an ozone-depleting potential of 0.02. This can be compared to say, HBFC-234 which has an ODP of 7.5. However, HCFC 123 was considered as having very few risks and a relatively small amount was needed to extinguish the fire.