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Foam: How it makes water a better firefighter

© Robert Moyer

Foam: How it makes water a better firefighter

Water, alone, can be an inefficient firefighting tool depending on fuel type, fuel loads and fire conditions. Water as it is converted to steam, has the ability to absorb and carry away heat. This happens at an expansion rate of 1700 to 1. Unfortunately, water's strong surface tension causes it to form small beads and roll off the fuel it is being applied to faster than it can absorb its full heat capacity. This makes water only five percent to fifteen percent efficient, thus requiring huge amount of it to extinguish some fires, not to mention long periods of time.

Most Class A foam concentrates are specifically formulated to make water more efficient. A combination of surfactants reduces the water surface tension. As a result the water can spread out over the surface area of the fire and penetrate deeper into Class A fuels. The deeper the water can penetrate into the fuel source, the quicker it can put out the fire. It can also help to protect exposure areas from radiant heat and airborne embers.

The benefits of a Class A foam concentrate to the rural fire service is enormous. Foam's all-white blanket coats and envelops the fuels source with a thick layer of water, where water alone would beaded up and rolled off. With the use of a foam, more water is now available, allowing the operator of the apparatus more time to establish a steady water supply. It also allows water more time to absorb its full heat capacity. A blanket of foam can also reduce the time taken to "mop up", overhaul and improve exposure protection.

Foam's white blanket reflects radiant heat away from the fuel source, insulates fuel by dispersing the heat away. It can also help smother the fuel and creates a fuel vapor barrier between the fuel and the fire. The foam blanket allows fuels such as wood, hay, carpets, cloth and insulation more time to absorb more water for greater heat resistance. With foam, firefighters can see where water has been applied, which is valuable in mop-up and overhaul operations. It is also helpful in combating attic or interior fires of large structures.

Two sets of experimental burns conducted in identical rooms showed that foam knocked down the fire thirty-five to sixty percent faster than water alone and took fifty to eighty percent less water to extinguish the fire. Faster knockdowns means less firefighter fatigue and stress, improved fire scene safety and reduced water damage.

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