Airman 1st Class Zachary Piper, 28th Medical Operations Squadron bioenvironmental engineering technician, checks the seal on the gas mask of Col. Susan Pietrykowski, 28th Medical Group commander, during a gas mask fit test at Ellsworth Air Force Base, S.D., July 1, 2013. In the past two weeks the 28th MDOS Bioenvironmental Engineer shop has served nearly 100 customers in need of a gas mask fit test in preparation of the operational readiness exercise beginning July 9. (U.S. Air Force photo by Airman 1st Class Alystria Maurer/Released)