Staff Sgt. Andrew McGee (left) and Airman 1st Class Justin Barajas, both with 71st Medical Group bioenvironmental engineering at Vance Air Force Base, Okla., mark evidence while walking a grid during an exercise April 15 on how to preserve and process a chemical or weapon-of-mass-destruction scene that may be a result of criminal activity. (U.S. Air Force photo/Capt. Tony Wickman)