Definition of Foam:
A foam is a substance formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams the volume of gas is large with thin films of liquid or solid separating the regions of gas.
Solid foams can be closed-cell or open-cell. In closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In open-cell foam, gas pockets connect to each other. A bath sponge is an example of an open-cell foam: water easily flows through the entire structure, displacing the air. A camping mat is an example of a closed-cell foam: gas pockets are sealed from each other so the mat cannot soak up water.
Types of Foam:
Broadly foams are divided into two types.
This foam produced by the reaction of aluminium sulphate (13%) solution with sodium bicarbonate (8%) solution.
6 nahc03 + Al2 (S0.) = 3Na2S04 + 2 Al (OH)3+ 6 C02
On small scale, foam is produced in portable extinguishers which are expelled by C02 gas produced during reaction.
For larger quantities the extinguisher can be made of higher capacities as desired and mounted on wheeled trolleys.
This foam is produced by agitation of foam compound (water having an additive) in the presence of air.
Characterized of Foam:
These substances have been around a long time for use as foams and emulsifiers to lammable non-polar liquid fuels. They can be used along with Dry Chemical Powders fectively. Its surface tension is so low that it forms a thin water film (abouto, 001′ inch).
Hence, this foam also known as “Light Water. The very thin film which in invisible, forms a very effective barrier that prevents fuel evaporation and is instrumental in extinguishing the fire.
These concentrates reused in fighting large petroleum and aircraft fires. The compounds mixed in watering the ratio suggested by the supplier, 3% or 6% generally. The mixture is then Dushed through a foam making device under pressure. The air sucked in forming bubbles grouped together which look like a rich leather.
This foams poured on the burning liquids gently and all owed to cover the entire surface gradually creating the blanketing effect.
Characteristics of Foam:
- Expansion Ratio (Normally 8: 1).
- Size of bubbles: Smaller the size, longer the life.
- Speed of spreading.
- Resistance to fuel/Heat.
- Shelf Life.
Mechanical Foam Generators:
Mechanical Foam Generators are a development of the self-inducing type Foam making branch. All the models of Mechanical Foam Generators designed to induce the foam compound and air in correct proportion to the quality of water flowing, to generate foam and deliver it through hose to the point of discharge. The backpressure against which the equipment can work is limited, and accordingly the length and size of hose used is important.
A minimum pressure of 150 lbs. P.s.i requires to operate these Generators, and, therefore, placed in the hose line close to the pump. Mechanical Foam Generators used to a limited extent in the Fire Service.
Foam Making Equipment’s:
- Foam making Branches.
- Depending upon the size these are named as.
- No 2 Foam Making Branch.
- No. 10 Foam Making Branch.
- No 20 Foam Making Branch.
- No 30 Foam Making Branch.
The principle of operation is identical for all these type of branches, the difference is in terms of their sizes and capacities.
As for example No 2 branches uses 50 ‘gallons of water to produce 450 gallons of foam per minute while No 10 branch uses 1. 00 gallons of water to produce800 gallons of foam per minute.
The sizes in which they are available together with operational data are as follows:-
|Type of M.F.G.||Water Intel Pressure (lbs. Psi)||Water Capacity (G.P.M.)||Foam Compound (G.P.M.)||Foam Delivered (G.P.M.)||Hose arid Nozzle Sizes|
|150||56||2||380||Upto200feet of 23/4″ hose with 1½”nozzle|
|5||900||Up to 200 Feet 4″ hose with2½” or 3″ nozzle, or up to 200 feet of twinned 2 3/4″ hose and 1½nozzle.|
|7||1250||Up to 200 Feet 4″ hose with3½” or 4″ nozzle, over 200-feet 6″ hose.|
|10||1800||Up to 200 Feet 6″ hose with 4″ nozzle.|
|14||2450||Up to 200 Feet 6″ hose with5″nozzle. Over200 Feet 8″ hose.|