Ten months ago, government safety officials warned that more than half of the nation's 60,000 pressurized rail tank cars did not meet industry standards, and they raised questions about the safety of the rest of the fleet as well.
Their worry, that the steel tanks could rupture too easily in an accident, proved prophetic.
On Thursday, a derailment in South Carolina caused a catastrophic release of chlorine: eight people died, 58 were hospitalized and hundreds more sought treatment. Thousands of people within a mile of the accident were driven from their homes.
And last summer, a derailment in Texas caused a steel tanker to break open, spewing clouds of poisonous chlorine gas that killed three people.
The causes of the accidents are still under investigation. But the devastation they have wrought shows why tank cars have become an increasing concern not just to safety investigators but also to domestic security officials worried that terrorists could turn tankers into lethal weapons.
The FBI warned in 2002 that al-Qaida might be planning to attack trains in the United States, possibly causing derailments or blowing up tank cars laden with hazardous materials. And after bombings on commuter trains killed 191 people in Spain in March, domestic U.S. security officials secretly persuaded one railroad to reroute toxic shipments that had routinely passed within four blocks of the Capitol in Washington, government officials said.
Federal authorities have been working with railroads and the chemical industry to improve security for trains. But there is still much to be done, particularly given the structural weaknesses of many tank cars, current and former federal officials say.
Just how ruptured tank cars can endanger a community was underscored three years ago when a Canadian Pacific Railway freight train derailed just outside Minot, N.D. Five tank cars carrying a liquefied type of ammonia gas broke open, releasing toxic fumes that killed one resident and injured more than 300.
The National Transportation Safety Board, in a report on the accident released last year, said that the steel shells on the five ruptured tank cars had become brittle, causing a "catastrophic fracture" that released clouds of toxic vapors. Those cars, the safety board found, were built before 1989 using steel that did not - as it does now - undergo a special heat treatment to make it stronger and less brittle. Tank cars built after 1989 use this specially treated steel.
