ELLSWORTH AIR FORCE BASE, S.D. – Staff Sgt. David Hall, 28th Medical Group bioenvironmental engineering journeyman, conducts a gas mask fit test on Airman 1st Class Anthony Sanchelli, 28th Bomb Wing still photography journeyman, July 7. During the fit test, the Airman will move his head up and down and side to side to mimic normal movements. It is intended to make sure the seal remains tight. (U.S. Air Force Photo/Airman 1st Class Corey Hook)