M-50 gas masks prepare to be prepped for fit testing at the 633rd Aerospace Medicine Squadron bioenvironmental office at Langley Air Force Base, Va., Feb. 9, 2016. Bioenvironmental conduct gas mask fit tests for U.S. Service members, ensuring they have a tight seal in the event of chemical warfare in a deployed environment. (U.S. Air Force photo by Senior Airman Brittany E. N. Murphy)