Staff Sgt. Ronald Reynolds, a 28th Civil Engineer Squadron emergency management technician, instructs Airmen on the fundamentals of a gas mask during chemical, biological, radiological, nuclear and environmental training at Ellsworth Air Force Base, S.D., March 14, 2018. During the course, instructors demonstrated how to properly store and wear mission oriented protective posture gear, cover military assets, and test surfaces for chemical agents. (U.S. Air Force photo by Airman 1st Class Donald C. Knechtel)