Approximately ten members of the 433rd Civil Engineer Squadron Fire Department pay tribute to the 9/11 firefighters who perished in the World Trade Center by walking up and down 110 flights of stairs during the September unit training assembly here Sept. 10, 2017. Most of the firefighters were in full gear with oxygen tanks and helmets. A dispatch audio recording from the World Trade Center towers was played during the event so participants and attendees could hear transmissions between first responders before the towers collapsed. (U.S. Air Force photo/Senior Airman Bryan Swink)