Kelly Byrne, a Washington D.C. firefighter and rope-rescue instructor, teaches 11th Civil Engineer Squadron firefighters about various knots used during elevator rescues May 6, 2015, on Joint Base Andrews, Md. Tying or connecting to a knot incorrectly could be fatal, so firefighters have to know how and when to use each knot required for different situations. (U.S. Air Force photo by Senior Airman Preston Webb)