Fire suppression guns fire an aqueous film-forming foam in the 3-Bay hangar during a final test of the fire suppression system Sept. 23, 2014, on Grand Forks Air Force Base, North Dakota. The suppression guns spray 110 gallons of foam per square inch onto the floor of the hangar to protect an aircraft in the event of a fire. (U.S. Air Force photo/Senior Airman Xavier Navarro)