Staff Sgt. Ismael Rodriguez, 28th Aircraft Maintenance Squadron sortie support supervisor, adjusts his mask prior to a gas mask fit test at Ellsworth Air Force Base, S.D., July 1, 2013. Bioenvironmental engineering technicians ensure gas masks fit properly on the wearers to guarantee they will remain unharmed by any chemical attacks. (U.S. Air Force photo by Airman 1st Class Alystria Maurer/Released)