Airman 1st Class Ryan O'Keefe, 11th Civil Engineer Squadron heavy equipment operator, tries on an M50 gas mask during a Chemical, Biological, Radiological and Nuclear Defense (CBRN) Survival Skills Training course on Joint Base Andrews, Md., Feb. 14, 2013. The M50 is a Joint Service General Purpose Mask and is standard DOD wide, a vast improvement to the previous M40. (U.S. Air Force photo/Airman 1st Class Nesha Humes)(Released)