The termination of burning by means of isolation consists in temporal disjoining of burning zone with combustible substance or oxidant.
For this purpose there are applied: hard sheet materials (metal sheets, asbest cardboard, asbestos-cement plates and etc.); hard fibrous materials (asbestos cloth, felt, tarpaulin and other close weaves); noncombustible loose materials (sand, powders, different fluxes); liquid materials (chemical foams, air-mechanical foams of different multiplicity and etc.); gaseous substances (explosion products or combustion materials). These compositions are used for extinguishing different substances and materials in any phase (hard, liquid and gaseous).
Hard sheet, fibrous material and noncombustible loose materials are used as primary fire extinguishants to eliminate burning of insignificant fires that have small areas and quantities.
Depending on the type of combustible material different types of foams are used for extinguishing the developed fires: chemical and air-mechanical of different multiplicity. Generally, foams are used for extinguishing the volatile flammable & combustible liquids, and for protection from ignition of different substances and materials.
Air-mechanical foams go out in foamy trunks and froth generators of middle and high multiplicity by means of mechanical mixing of air with aqueous solution of foaming agents (ПО-1, ПО-1Д, ПО-3А, ПО-6к, “Сампо”, Поток-2 & etc.).
Air-mechanical foams can contain from 8 up to 99.6% of air and from 17 up to 0.4 % of aqueous solution of foaming agent.
The process of extinguishing the flame of volatile flammable & combustible liquids with the help of foams takes place in such a way. The foam as compact streams is supplied on the surface of liquid, over which it spreads and collects.
The air-mechanical foams of low and middle multiplicity move with mean speed 0.34 m/s over a surface of the frosting liquid, and at putting of foam on the liquid surface being burn, the speed of its moving decreases by removing from the foam generator. The foam is collapsed constantly under an influence of thermal radiation of a flame and heated combustible liquid, and in a certain moment the foam amount that is collapsed becomes equal to the foam amount supplied to burning zone. The state of mobile equilibrium begins. That foam could promote on the big distances and cover all surface of a liquid, which burns, its charge should exceed receipt owing to destruction in a burning zone.
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