FOAM FIRE PROTECTION SYSTEMS
Foam systems come in two types, as follows:
Low Expansion, where the bubble expansion ratio is small (less than 20 to 1) and the bubble contains a high water
content.
Medium and High Expansion, where the expansion ratios are greater from 20 to 1 up to 1,000 to 1. At these
expansion ratios, the bubble water content is low and the bubble is relatively light. The foam bubbles are made by
mixing a foam concentrate with water to make a foam solution. The foam solution is then mechanically agitated to
form bubbles.
Low Expansion Foam Fire Extinguishing Systems are applicable to special hazards, usually involving flammable or
combustible liquids, such as storage tanks. These systems discharge foam bubbles over the liquid surface to
provide a cooling, smothering blanket which progressively covers the liquid surface and extinguishes the fire. The
foam blanket can prevent vapor production for some time. Aqueous film-forming foam (AFFF) functions in a similar
manner, but with one notable difference: AFFF is capable of producing water solution films which float on the
surface of the liquid and help suppress vapor production. However, this beneficial "film" is obtained with some loss
of burn-back resistance.
High Expansion foam systems are applicable to areas where it might be desirable to fill the space with foam in
order to exclude air and smother the fire. Examples of such areas include basements and warehouses.