How Foam is Generated
A constant amount of foam concentrate is added to water by means of a proportioner. The resulting mixture of water/foam concentrate is expanded with air in the foam generator.
If the proportion of air is low a heavy “wet” foam is produced and a high proportion of air produces a medium "moist" to light "dry" foam. In any case, the volume of foam produced is many times greater than the volume of the water/foam concentrate solution.
The Induction rate
specifies the percentage ratio of foam concentrate added to water. At 3% induction rate, for example, 3 parts of foam concentrate are mixed with 97 parts of water.
During fire fighting operation, the foam concentrate is added by means of a proportioner or pump premixer either at the water pump, in the hose line, at the foam generator or in the central foam station. The induction rate is set at the proportioner or the pump premixer and usually varies (according to the type of foam concentrate, type of flammable material and the application device used) between 1 and 6 %. When using a synthetic foam concentrate as wetting agent 1 % is added.