U.S. Air Force Airman 1st Class Alex McClendon, 633rd Aerospace Medicine Squadron bioenvironmental engineer technician, performs a gas mask fit test on Senior Airman Sarah Lowry, 633rd AMDS bioenvironmental engineer technician at Langley Air Force, Va., Jan. 9, 2015. During the test, Lowry looked up and down and side to side to help ensure masks fits properly and to pass the fit test. (U.S. Air Force photo by Airman 1st Class Areca T. Wilson/Released)