Foam concentrates, how do they work ?
REMINDER ABOUT THE PROCESS OF COMBUSTION :
THE COMBUSTION :
Combustion is a chemical oxidation reaction between a FUEL and a COMBUSTION AGENT in the presence of an ENERGY source.
- Class A (wood, cardboard, paper, fabric, etc.),
- Class B (petrol, oil, white spirits, etc.),
- Class C (gas such as propane, butane, acetylene, hydrogen,
- Class D (finely divided metals such as aluminium powder,
steel wool, magnesium, etc.).
COMBUSTION AGENT :
- Oxygen in the air,
- Oxygenated water,
- Nitric acid,
- Mechanical due to friction,
- Electrical (lightning or static electricity),
- Chemical, biochemical, solar, etc.
THE FIRE :
Fire is the result from the interaction between these three elements: fuel, combustion agent and energy. Removing any one of these elements results in the fire being extinguished.
HOW FIREFIGHTING FOAM HELPS TO EXTINGUISH FIRES?
The effects of extinguishing foam:
1/ Separation effect: the layer of foam on the surface of the fuel limits the oxygen supply and thus extinguishes the fire.
2/ Isolation effect: the foam has high air content, which means low thermal conductivity. Therefore it can be applied to surfaces which are not yet on fire to limit the spread of the fire.
3/ Cooling effect: The water in the foam bubbles evaporates on contact with hot surfaces. The evaporation phase consumes a huge amount of energy to change water from its liquid state to a gas state, therefore removing or reducing the energy needed for combustion.