CHICAGO -- For two decades, one of the most commonly used type of rail tanker has been allowed to haul hazardous liquids from coast to coast even though transportation officials were aware of a dangerous design flaw that almost guarantees the car will tear open in an accident, potentially spilling cargo that could catch fire, explode or contaminate the environment.
The rail and chemical industries have committed to a safer design for new tankers but are pressing regulators not to require modifications to tens of thousands of existing cars, despite a spike in the number of accidents as more tankers are put into service to accommodate soaring demand for ethanol, the highly flammable corn-based fuel usually transported by rail.
Derailments have triggered chemical spills and massive blasts.
The tanker, known as the DOT-111, is a workhorse of the American rail fleet, with a soda-can shape that makes it one of the most easily recognizable cars. The tanker itself is not suspected of causing derailments, but its steel shell is too thin to resist puncture in accidents. The ends are especially vulnerable to tears from couplers that can rip off between cars. Unloading valves and other exposed fittings on the tops of tankers can also break during rollovers.
The flaws were noted as far back as a 1991 study.
An Associated Press analysis of 20 years' worth of federal rail accident data found that ethanol tankers have been breached in at least 40 serious accidents since 2000. In the previous decade, there were just two breaches.
The number of severe crashes is small considering the total mileage covered by the many tankers in service. But the accident reports show at least two people have been killed by balls of flame, with dozens more hurt. And the risk of greater losses looms large.
The rail and chemical industries and tanker manufacturers have acknowledged the design flaws and voluntarily committed to safety changes for cars built after October 2011 to transport ethanol and crude oil. The improvements include thicker tank shells and shields on the ends of tanks to prevent punctures.
But under their proposal to regulators, the 30,000 to 45,000 existing ethanol tankers would remain unchanged, including many cars that have only recently begun their decades-long service lives.
The National Transportation Safety Board asked in March for the higher standards to be applied to all tankers, meaning existing cars would have to be retrofitted or phased out.
The federal Pipeline and Hazardous Materials Safety Administration, part of the U.S. Department of Transportation, is considering both arguments, but the regulatory process is slow and could take several years, experts said.