No one knows, because no government agency has ever assessed plants' preparedness for an attack, according to a report released this week by the General Accounting Office, the investigative arm of Congress.
The report found that chemical plants are not required by any law to assess their security risks and make an effort to reduce them - and that no federal agency has evaluated the security preparedness of U.S. chemical plants.
The report cited an EPA study that found 123 chemical plants have a worst-case scenario where more than a million people would be at risk if a cloud of toxic gas were released.
Another 700 chemical facilities could each potentially threaten at least 100,000 people and about 3,000 facilities could each potentially threaten 10,000 people, the report said.
"To date, no one has comprehensively assessed the security of chemical facilities," the report said.
CIA Director George J. Tenet warned Congress a year ago that al-Qaida terrorists have considered attacks against industrial chemical facilities, among other targets. The Department of Homeland Security, in raising the nation's alert level this past February, said nuclear power plants and industrial chemical plants "remain viable targets."
EPA may have authority under the Clean Air Act to order chemical plants to enhance security, but EPA officials told the General Accounting Office that they have not acted so far because they don't want to trigger a legal battle with the $450 billion chemical industry.
To the industry's credit, many plants have voluntarily shored up security since 9/11, but the extent of those actions is unknown, the report said.
The American Chemistry Council, which represents about 1,000 chemical facilities, said it supports development of a national strategy on industry security and is already voluntarily addressing vulnerabilities.
Sen. Jon Corzine (D-NJ) is sponsoring a bill that would require chemical plants to upgrade security, switch to safer chemicals wherever possible, and reduce the inventories of dangerous chemicals.
Rep. Frank Pallone (D-NJ) plans to introduce the legislation in the House this week.
"The GAO's findings should serve as a wake-up call to the Bush administration that it can no longer drag its feet on chemical security and must immediately address the serious vulnerability of our nation's chemical facilities," Pallone said.
Homeland Security Secretary Tom Ridge said that security at chemical plants is a worrisome issue that both federal and state authorities have been trying to grapple with.
"There's no question that when we take a look at a chemical facility, the possibility that terrorists could use that economic asset and turn it into a weapon is something that we need to be concerned about," Ridge told reporters.
