Fire Suppression Systems

Gaseous fire suppression systems work by reducing the oxygen level to a point where combustion is no longer possible or by interferring with the chemistry of combustion.

Carbon dioxide

Still commonly used in industrial applications is generally the most effective. The release of the CO2 into the protected area pushes the existing air (and consequently oxygen) out into the surrounding areas.

No oxygen - no fire.

CO2 is toxic.

Disadvantages: CO2 displaces the O2, therefore there is a danger of asphyxiation. It is essential that consideration is given to the safety of personnel in the protected area and those areas adjacent to it. CO2 being heavier than air should not normally be used in basements or confined spaces.

Non-asphyxiating gases

Until recent times theses systems used chemicals belonging to a group known as halogenated hydrocarbons, commonly referred to as HALONS e.g. Halon 1211 and Halon 1301.

a) Chemical interferes with the combustion process.
b) Inert gases reduce the CO2 level to a point which supports life (respiration) but is below the threshold which support combustion.

Halons were phased out following the Montreal Protocol 1997 due to the damage caused to the earths ozone layer.

There is now a quite wide range of alternatives, some using chemicals, others mixtures of nitrogen, argon etc. available. The choice of non-asphyxiating medium is a specialist subject and we bring in experts to advise and do detailed designs.

Advantages -
danger of asphyxiation removed.

Disadvantages -
not always as effective as CO2.
may still have some ozone depletion potential.

With all gaseous fire suppression systems consideration in the design has to be given to ensuring the room protected will retain the gas and that the increase in room pressure (above normal atmospheric pressure) will not damage the structure of the room / building.

Powder

Chemical powder which reacts with flame to extinguish fire.

These systems are frequently used to protect heavy mobile plant (engine compartments), particularly in timber mining and rail transport vehicles