Airman 1st Class Kimani Petersen, a 28th Maintenance Squadron aerospace ground equipment technician, quickly dons his gas mask during chemical, biological, radiological, nuclear and environmental training at Ellsworth Air Force Base, S.D., March 23, 2018. During the course, students learned 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)