Better Water

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. Hundreds of these concentrates are available today, but the majority fall into four basic categories: Class A Foam, Class B Foam, Emulsifiers and Gels. Here’s an overview of what each one does for you.

Class A

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 (see Fig. 1).

Fig. 1

Water

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” (see Fig. 2).

Fig. 2

Water + Foam

Class A concentrate is simply a surfactant, similar to dish-washing 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 (see Fig. 3). 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.

Fig. 3

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.

Class B

Designed for use on Class B-type fires or two-dimensional fuels, it forms a film over a contained fuel to extinguish and prevent re-ignition. Unlike Class A foam, manufacturers of Class B recommend the percentage of foam concentrate to water mixture based on the fuel to which it is applied. The most common proportioning rates are 1%, 3% and 6%. Some brands offer dual-usage concentrate, which may be applied on hydrocarbon and polar solvent fuels. Typically these will indicate two proportioning rates such as 1% x 3%, 3% x 3% or 3% x 6%. Since high volumes of water and concentrate are typically utilized; cost, storage and logistical requirements are important to evaluate. The newer 1% versions may cost more per gallon of concentrate, but less per gallon of solution. They also require very accurate proportioning systems.

Other Concentrates

Emulsifiers are another type of additive used to provide long-term vapor suppression and aid in hydrocarbon recovery. Gels have proven to be excellent insulators and provide long-term exposure protection. Mixture rates for these can vary depending on application.

Performance Comparison

Comparison tests performed by Los Angeles County Fire Department on three identical 1100 sq./ft. homes demonstrate the powerful results of CAFS and Class A foam solution versus plain water.

  • Water: 73 gallons (276 liters)
  • Foam: 44 gallons (167 liters)
  • CAFS: 16 gallons (61 liters)
    • 79% better than water
    • 64% better than foam
  • Water: 6:03 minutes
  • Foam: 1:45 minutes
  • CAFS: 1:28 minutes
    • 76% better than water
    • 17% better than foam
  • Water: 320 gallons (1211 liters) *
  • Foam: 95 gallons (360 liters)
  • CAFS: 45 gallons (170 liters)
    • 86% better than water
    • 53% better than foam

* After 225 gallons (852 liters), IC ordered foam to aid overhaul