A U.S. Air Force Airman, assigned to the 633rd Civil Engineer Squadron, inspects the seal on his M50 joint service general purpose mask during Prime Base Engineer Emergency Force day training at Joint Base Langley-Eustis, Virginia, Jan. 25, 2018. Airmen must be able to fasten their masks in 9 seconds or less. (U.S. Air Force photo by Airman 1st Class Anthony Nin Leclerec)