foam fire extinguisher

Portable foam type fire extinguishers are best suited to put out class B’ fires involving flammable liquids like oil, solvents, petroleum products, etc. The foam expelled by activation of the extinguisher, forms a blanket over the surface of the liquid on fire and cuts out contact of the burning liquid with air and thus extinguishing the fire.

What is foam fire extinguisher , foam fire extinguisher image

There are basically two ways of producing foam from portable fire extinguisher: 

  • By chemical reaction
  • By self-aspiration of a foam solution through a foam branch pipe (mechanical foam).

9-Liter Chemical Foam Type fire Extinguisher :

The chemical foam extinguisher consists of a cylindrical inner container and a large cylindrical outer container. The inner container is usually made of polythene and filled with 680 gm aluminum sulphate mixed in water and the outer container with 680 gm of sodium bicarbonate mixed in water. 

A wheel cap fitted with T’ handle connected with diaphragm works as a blank seat for inner container so that the two solutions cannot be mixed accidentally. The two solutions, when mixed, produce aluminum hydroxide, sodium stulphate and carbon dioxide. The pressure created by the formation of carbon dioxide gas forces the foam out.

Al(SO)3 + 6NaHCO, = 2AI(OH)+3Na,SO, + 6CO2

A 6-meter jet can be maintained for a period of 30 seconds and discharge of expelled foam must be completed in 90 seconds.

Foam solutions are electrically conductive and hence not recommended for use on fire involving live electrical/electronics equipment. I Though foam used as a spray is less conductive than straight stream, because foam is cohesive and contains materials that allow water to conduct electricity, a spray foam is more conductive than a water fog.

Method to Operate foam fire extinguisher :

Pull the plunger to open the valve and rest it on the notch provided. Block the nozzle with finger and turn the extinguisher upside down twice, at the same time shaking thei extinguisher to ensure mixing of the two solutions.

When the pressure is felt on the finger, point the nozzle towards the fire, keeping extinguisher upside down. Direct the jet at the inner edge of the container or at an adjoining vertical surtace above the level of the burning liquid. If this is not possible, direct the jet in an arc with gentle sweeping movement allowing the foam to float on the surface of the liquid.

The foam jet should not be directed into the liquid, as there is a possibility of splashing the burning liquid on to the surrounding and spreading the fire.

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