Army Staff Sgt. Derek Leonhardt, assigned to B Troop,

Army Staff Sgt. Derek Leonhardt, assigned to B Troop, 1st Squadron (Airborne), 40th Cavalry Regiment, 4th Brigade Combat Team (Airborne), 25th Infantry Division, U.S. Army Alaska, reacts to CS gas exposure during chemical, biological, radiological and nuclear defense training on Joint Base Elmendorf-Richardson, Alaska, Wednesday, April 13, 2016. The training culminated with masked Soldiers entering a sealed chamber filled with CS, then removing their protective gear to promote confidence in their equipment. CS, technically known as 0 chlorobenzalmalononitrile, is a solid white powder mixed with a dispersal agent and commonly referred to as tear gas. (U.S. Air Force photo/Justin Connaher)