Airman Daniel Giulian, 437th Aircraft Maintenance Squadron crew chief, transfers liquid oxygen from a tank to a C-17 Globemaster III at dusk on Feb. 11, 2015, at Joint Base Charleston, S.C. When exposed to open air, the minus-297-degree LOX evaporates into a gas. Liquid oxygen is used as a means of distributing breathable air to aircrew members and passengers above 10,000 feet above sea level. The C-17 can hold approximately 155 gallons of LOX. (U.S. Air Force photo/Senior Airman Dennis Sloan)