In the context of fire suppression, what does 'high expansion' foam refer to?

High expansion foam is specifically designed to create a large volume of foam from a relatively small amount of liquid. This type of foam can fill and envelop larger areas, making it particularly effective for suppressing fires in spaces with high ceilings or large open areas, such as warehouses or ship holds. The foam works by trapping air, which expands its volume significantly—often expanding to more than 1,000 times its original liquid volume. This expansion capability allows it to displace oxygen in the area of the fire, thus suffocating the flames and providing a barrier against heat.

While foam density and longevity can vary among different foam types, the characteristic feature of high expansion foam is its ability to expand and cover larger spaces, making it ideal for specific fire suppression scenarios.