Why is adding additional gallons or litres of water per cfm not generally accepted by knowledgeable CAFS users?
Adding 2 to 5 gallons (8 to 20 litres) of water per scfm makes a milky, very low expansion foam. This very thin layer disappears quickly. This idea is a carry over of water thinking where you must use as much water as possible. Early CAFS research quickly proved that medium foam was far more effective and safer. Extra water foam has about the same knockdown capability as aspirated foam and is several steps below what CAFS foam can offer. One hundred gallons (375 litres) of extra wet foam solution 1 – 1.5: 1 expansion makes about 150 gallons (560 liters) of foam. 42 gallons (160 litres) of CAFS foam solution on medium foam makes 375 gallon (1420 litres) of foam. It should be noted that extra water foam increases the hand line weight dramatically and cannot be pushed as far, at a given pressure, as true CAFS foam can and more run off occurs. It takes a knowledgeable CAFS user a few seconds at a comparison demonstration to see that there is really no comparison between extra water foam an
