ELLSWORTH AIR FORCE BASE, S.D. -- (Left to right) Senior Airman Hugh Blacketor, 28th Civil Engineer Squadron heating, ventilation and air-conditioning journeyman, uses two hand-held chemical detectors to check for simulated contamination on Airman 1st Class Michael Mays, 28 CES structural apprentice, during a phase II operational readiness exercise, Aug. 24. During the exercise, Airmen are tested on their knowledge and abilities while under simulated chemical attacks. (U.S. Air Force photo/Airman 1st Class Anthony Sanchelli)