A 20th Civil Engineer Squadron firefighter, pulls a lever controlling compressed air foam at Shaw Air Force Base, S.C., March 10, 2014. The three tank system is a mixture of air, foam and water which cools down a structure that is on fire by producing millions of bubbles that trap British thermal units, which are the amount of heat required to raise the temperature of one pound of water. (U.S. Air Force photo by Airman 1st Class Jensen Stidham/Released)