For years, fire departments have been utilizing chemicals to improve the effectiveness of water, thereby creating greater knockdown efficiency and increased firefighter safety. The additives in this water are sold in high concentration and require mixing to form a solution at percentages dictated by the application, or as recommended by the manufacturer.
Knockdown in 6 Seconds
The Viroqua, Wisconsin Fire Department responded to a fire in this 1890s two-story brick schoolhouse located 4 miles (6.45 kilometers) outside of town. With only 750 gallons (2839 liters) of water on board and no hydrants nearby, this fire could have quickly become a real challenge. But this progressive department arrived on the scene equipped with a FoamPro 2001 foam proportioning system.
Knockdown was accomplished in 6 seconds with 33 gallons (125 liters) of water and .17 gallons (.64 liters) of foam concentrate, using a 200 ft., 2-1/2” line with water flow of 328 gpm (1242 L/min) and 0.5% of Class A foam concentrate injected directly into the water stream.
Ninety-seven percent of today’s fires are Class A-type fueled by modern synthetic materials. With flashover faster than ever, can you afford not to have: faster knockdowns, improved firefighter safety, less water usage, reduced rekindles, quicker company returns, excellent exposure protection, faster clean-up, less property damage, evidence preservation and limited environmental damage?
Fire departments only recently are fully embracing the use of Class A foam. Designed for use on any Class A fire or three-dimensional fuel, Class A foam solution is a far superior firefighting agent than plain water . . . up to 3 to 4 times more effective! A look at the fire triangle will help explain why.
By absorbing heat, water attacks one leg of the triangle. A natural characteristic of water called surface tension “holds” water together resulting in larger droplets. This limits heat absorption for a given volume of water as a small percentage (outer 10% of droplet) actually removes heat while the majority (inner 90% of droplet) runs off the fuel source and “out the front door”.
Water + Foam
Class A concentrate is simply a surfactant, similar to dishwashing soap, that reduces surface tension. When added to water, the resulting foam solution consists of many smaller droplets with much more surface area, allowing faster heat absorption. An example would be like cooling a glass of water with a single ice cube rather than crushed ice of the same volume. The crushed ice would cool it faster. In addition to creating smaller droplets, reducing the surface tension allows water to penetrate the fuel faster and deeper, dramatically raising the moisture content.
This isolates the fuel leg of the triangle, increasing the resistance to burn. Finally, foam solution separates the fuel from oxygen with a vapor-securing barrier that provides excellent protection.
The proportion of Class A foam concentrate to water is dictated by use. A common rate for initial attack is 0.5%; overhaul 0.2% and exposure protection 1.0%. Application of the final solution can be achieved through a number of different mediums, including your standard nozzles, or specifically-designed aspirating nozzles.
Water + Foam + Air (CAFS)
Compressed Air Foam Systems (CAFS) is another technology making Class A foam even better. By injecting air into the solution, “bublets”, consisting of air surrounded by foam solution, are formed, which delivers a more efficient fire stream. The bubble structure is also much stronger and the additional energy from the air increases stream reach.