Simulated Subway Attack
David Silcott, General Manager of IBX Biodefense, adds fluid to a machine releasing gases and fluorescent particles into Boston's subway tunnels, Friday, Aug. 20, 2010, during an exercise at the Park Street Subway station in Boston. The exercise was intended to study how toxic chemicals and lethal biological agents could spread through the nation's oldest subway system in a terrorist attack. (AP Photo/Josh Reynolds)
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