U.S. Air Force Senior Airman Justeen Swihart, a 97th Medical Group bio-environmental engineering technician, tightens a gas mask on Airman 1st Class Don Nathaniel Wentzel, 97th Medical Group bio environmental engineering tech, during a quantitative fit test at Althaus Air Force Base, Okla., Jan. 10, 2012. Quantitative fit tests ensure issued gas masks properly fit users to increase personal protection during a chemical, biological, radiological or nuclear attack.