Foam is a mass of air-filled bubbles and it consists of water, foaming agent and air. Fire fighting foam is highly fire-resistant as it contains various substances which successfully inhibit the burning process. The foam is created by adding air at the spray nozzle to the admixture of water and foaming agent.
Under the NFPA 11 standard, the foam is classified according to expansion (the factor showing the quantity of the foam created from the foaming agent) as:
- Low expansion foam (expansion 4-19)
- Medium expansion foam (expansion 20-200)
- High expansion foam (expansion >200)