A method of fighting underground fires developed in the United States, and somewhat similar to the British foam plug. It involves the formation of a high-expansion noncombustible foam. Large volumes of the foam are drawn or blown over and around the fire until it can no longer be sustained due to lack of oxygen. The foam is made from 1500 ammonium lauryl sulfate and 1 gal (3.8 L) of solution is used for each 250 to 300 ft₃/min (7.1 to 8.5 m₃/min) of air passing through the net.