Senior Airman Gregory Rackley, 56th Occupational Medicine Readiness Squadron bioenvironmental engineering technician, instructs Senior Airman Joseph Bowden, 62nd Aircraft Maintenance Unit crew chief, on the procedure to tighten a gas mask during a fit test Jan. 14, 2020, at Luke Air Force Base, Ariz. The technicians administer fit tests for individuals who are deploying; individuals perform various movements while wearing the gas mask to test how well it fits to their face. Bioenvironmental engineering’s mission is to provide reliable health risk expertise to optimize human performance and prevent adverse health effects of Airmen. (U.S. Air Force photo by Airman 1st Class Brooke Moeder)