U.S. Air Force Senior Airman Sarah Lowry, 633rd Aerospace Medicine Squadron bioenvironmental engineer technician, dons a gas mask before a fitting at Langley Air Force, Va., Jan. 9, 2015. Gas masks are tested to guarantee masks fit properly and no harmful chemicals can seep through. (U.S. Air Force photo by Airman 1st Class Areca T. Wilson/Released)