Three recent incidents in Iraq have involved explosives combined with chlorine, which can be toxic and even deadly when it's inhaled as a gas. Such bombs have US officials worried that terrorists are resorting to chemical warfare. Could it happen here? Since September 11, reporters have been demonstrating the vulnerability of chemical plants, some near major cities. But the Bush Administration has resisted efforts to impose tough safety measures; new federal rules could undermine efforts by states. How serious is the risk to the public? Do corporate officials or government bureaucrats know best what needs to be done? We hear from journalists, industry and national security experts.