Airman Marlene Zeledon, 11th Civil Engineer Squadron emergency management journeyman, tests a chemical agent during a training exercise in the Memorial Tunnel at the Center for National Response in Gallagher, WV., March 17, 2015. This training is part of the annual Black Flag exercise for first responders. Zeledon is stationed at Joint Base Andrews, Md. (U.S. Air Force photo/Senior Airman Joshua R. M. Dewberry)

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