Okie firefighters from the 507th Civil Engineer Squadron climb the stairs of the fire training tower during their 7th annual fire climb Sept. 11, 2016, at Tinker Air Force Base, Okla. Each year, Reservists climb up and down the fire-training tower to complete the 18 laps within 56 minutes, the amount of time it took the South Tower of the World Trade Center to collapse. (U.S. Air Force photo/Master Sgt. Grady Epperly)

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Photo by: Master Sgt. Grady Epperly |  VIRIN: 160911-F-YA646-0094.JPG