A secondary method of fighting underground fires, devloped in Great Britain in 1956. It consists of filling the fire area with soap bubbles which are moved forward by the air current. The foam is produced by passing the air current through a cotton net, saturated with a dilute solution of detergent, which is stretched across the mine roadway. The air passing through the net forms bubbles 1/2 to 1-1/2 in (1.3 to 3.8 cm) in diameter which honeycomb and form a plug of foam that tends to quench the fire and reduce its temperature to a point where it can be attacked directly and without protective clothing.