A firefighter tests the PH-levels of an unknown substance to determine its threat during a joint chemical, biological, radiological, nuclear and high-yield explosive (CBRNE) threat exercise at Fort Eustis, Va., Jan. 28, 2016. The firefighters donned CBRNE protective gear to simulate real-world procedures that protect them from the dangers of CBRNE materials. (U.S. Air Force photo by Staff Sgt. Natasha Stannard)