Keisha Faw, left, a gas mask fit tester with the U.S. Air Force 48th Aerospace Medicine Squadron, and Capt. Tony Kasallis, a general dentist with the 48th Dental Squadron, review gas mask fitting exercises, in the deployment center at Royal Air Force Lakenheath, United Kingdom, Sept. 22, 2010. The sheet prescribes five 40-second exercises to ensure a proper gas mask fit.