High-expansion foams are those that expand in ratios of over 100:1. Most systems produce expansion ratios of from 400:1 to 1000:1. Unlike conventional foam, which provides a blanket a few inches over the burning surface, high-expansion foam is truly three dimensional; it is measured in length, width, height, and cubic feet.
High Expansion Foam Concentrate and water are mixed in the correct proportion by various methods to form a foam solution. This solution flows to the High Expansion Foam Generator (HEFG) with a water powered motor. It is then discharged through a nozzle onto a fine mesh stainless steel screen.
A rotating fan (powered by the water motor) in the generator forces large volumes of air through the stainless steel screen as the foam solution is sprayed onto it. The air mixes with the foam solution to form a large discharging mass of stable bubbles at a rate of up to 940 gallons of expanded foam for each gallon of foam solution
Points to ponder in high expansion foam:
The following items should also be considered:
- Because of the light weight of high expansion foam, outdoor use is impractical in most cases.
- High expansion foam must be used in a volume confined by walls.
- Foam should not be used on water reactive materials or energized electrical equipment.