Firefighter Greg Riley calls for helps as United States Navy student Bethjamie Narveaz lies on the concrete porch of the galley during a mock chemical attack at Naval Air Station - Meridian near Meridian, Mississippi, May 5, 2006. The chemical identified as Tabun was the substance used during the attack. According to the Centers for Disease Control and Prevention, tabun is a man-made nerve agent that can be used in chemical warfare. Tabun is also known as "GA" and is colorless, clear and tasteless liquid that can be used as a gas if heated. REUTERS/Kyle Carter