An Airman checks the seal on his gas mask during Chemical, Biological, Radiological and Nuclear Defense training, Dec. 4, 2017, at Aviano Air Base, Italy. More than 500 Aviano Airmen attended a training rodeo to receive hands-on training in basic Self-Aid Buddy Care and Chemical, Biological, Radiological, Nuclear and High-Yield Explosive Defense skills. (U.S. Air Force photo by Airman 1st Class Ryan Brooks)