YOKOTA AIR BASE, Japan -- Senior Airman Richard Riley, 374th Aerospace Medicine Squadron bio-environmental engineering technician, and Senior Airman Travis McCallum, 374th Civil Engineer Squadron emergency management technician, identify a sample of a simulated suspicious substance found at a residential tower during an Operational Readiness Exercise at Yokota Air Base March 9. During the scenario, a substance was found during a 374th Security Forces Squadron building sweep following a simulated call regarding vandalism. (U.S. Air Force photo/Staff Sgt. Samuel Morse)