Foam Systems have been traditionally used to provide fire protection in the chemical and petroleum industries as well as in militarywater-mist-small installations. The overall effectiveness of current fixed-foam systems which incorporate aspirating - type nozzles and blower-type foam generators is limited since they are unable to provide foam with high injection velocities.
Further, the foam produced employing traditional systems is not as stable and consistent. Expansion ratios are not as high as desired for some applications , because the air to generate foam at the nozzle which comes from the fire environment may be contaminated.
However, if compressed air is used for foam generation, the foam possesses superior quality and substantial injection velocity as well as requiring a much smaller quantity of water and foam concentrates. Compressed Air Foam (CAF) is generated by injecting air under pressure into a foam solution stream.
The process of moving the solution and air mixture through the hose or piping , if done correctly , forms a foam, The energy for the CAF comes from the combined momentum of the foam solution and air. One significant advantage of such systems is the increased momentum of the foam, enabling it to penetrate flames and reach the fuel surface. Another advantage of CAF is that it possesses greater stability with respect to drainage (foam does not collapse easily) than air-aspirated foams, since it is characterized by a narrow distribution of bubble sizes. Early attempts to adapt CAF to fixed installations failed, owing to two fundamental difficulties:
To overcome these difficulties, a means of producing CAF using class A and Class B foam concentrates in a fixed piping system using a innovative distribution nozzle was developed. Foam break up which prevented the development of this technology in the past was avoided by careful engineering design of the nozzle and the piping system.
Full-scale fire test were conducted to evaluate the performance of a prototype CAF system.
The test demonstrated the superior performance of the CAFS system in extinguishing both liquid fuel and wood crib fires, using smaller amount of water. Also, CAF requires a smaller amount of foam concentrate to provide effective suppression compared to systems based on air-aspirated nozzles. Assessment of prototype CAF system, proved the superiority in extinguishing simulated fuel spill and transformer fires.
CAF systems are now being developed for a wide range of commercial applications.