Halogen hydrocarbon and powder-like extinguishants.

The mechanism of burning termination of halogen hydrocarbon compositions consists in that in burning zone extinguishants are supplied, that cause the break of chain reactions of burning.

Such extinguishants have: low-boiling point and at heating easily go into the vaporous state; small thermal stability; ability to decompose to parts, actively reacting with intermediate combustion products with formation of noncombustible substances. On the surface facilities and aircraft of civil aviation ethylene bromide (СН₂Br₂), ethyl bromide (С₂Н₅Br), trifluorobromomethane (СF₃Br), tetrafluordibromomethane (С₂F₄Br₂) are used.

Their high fire-fighting ability is the feature of these substances at their comparatively small concentrations which in a few times less than concentrations of gas and steam extinguishants (СО₂, N₂, water vapour and etc.).

High fire-fighting efficiency of haloid hydrocarbons is conditioned by the increased chemical activity of products of their thermal decomposition, actively reacting with the intermediate combustion products.

The high corrosiveness to the magnesium and aluminium alloys (basic materials used in aircraft construction), and also high toxicity of pyrolysis products belong to disadvantages of haloid hydrocarbons as extinguishants.

The more mean have powder-like extinguishants which can be used for extinguishing practically all types of burnings, including the fires of magnesium alloys, regardless of area and quantity of fire. Supply of extinguishants in burning zone is carried out by means of movable and stationary facilities.

Main factors that affect on the reaction of burning are: termination of burning due to increase of heat removal from the flame (reaction zones) — so called principle of fire-resistance; dilution of vapour of combustible substance with a powder-like cloud and gaseous products of powder decomposition; inhibition of combustion process by the products of powder pyrolysis, and also pyrolysis break of reaction chains on the surface of hard parts of powder; cooling of space of burning zone as a result of heating of parts of powder.

Powder-like extinguishants have the following qualities promoting to their fire-fighting practice application: they quickly eliminate burning at their comparatively small charges; a powder-like cloud is non-electroconductive; they shield the thermal radiation of flame;

they do not freeze; the corrosion of metals is not caused by their in the absence of moisture; they do not exert influence on the substances and materials, that fall under extinguishing.

At the same time, powder-like extinguishants have the following disadvantages: small cooling effect; they are able to deteriorate in store and form balls; burning zone is not looked over a powder-like cloud.