The National Transportation Safety Board this week determined that a broken rail, due to inappropriate bond wire welds on the rail in an area of known soft ballast conditions, was the probable cause of the derailment of a Canadian National Railway freight train near Tamaroa, Illinois.
The accident occurred on Feb. 9, 2003, when a northbound Canadian National train, traveling between Memphis and Chicago at about 40 mph, derailed 22 of its 108 cars. Nineteen of the derailed cars were tank cars that contained hazardous materials. A fire ensued and there was a release of vinyl chloride, methanol, phosphoric acid, hydrochloric acid and formaldehyde from several of the tank cars.
About 850 residents within a 3-mile radius of the derailment were evacuated, including the entire village of Tamaroa. There were no fatalities or injuries. Damages to track, equipment and clean-up costs associated with the accident totaled about $1.9 million.
“Serious accidents like this point up the need for rigorous maintenance standards to ensure the safety of tracks over which hazardous materials are carried,” said NTSB Chairman Ellen Engleman Connors. “It is an area that demands close attention by both the industry and government.”
The Board found that the derailment occurred when a rail broke near an insulated rail joint where bond wires had been welded to the rail head. The exothermic welding procedure used by Canadian National workers produced untempered martensite, a brittle structure in the steel that made the rail susceptible to fatigue cracking.
The known muddy, soft ballast condition in the area of the insulated joint provided inadequate support for the track and increased the amount of rail flexing which, in turn, significantly increased stresses on the rail. The increased stresses, the Board said, caused the propagation of fatigue cracks that had originated in the areas of untempered martensite at the rail head, leading to a failure of the rail only 17 days after it had been installed.
As a result of the investigation, the Board recommended to ERICO Products Inc., the developer of the exothermic welding process, that it revise its instructions for users to make them aware that the welds create untempered martinsite that can, under certain conditions, lead to fatigue cracking and rail failure.
The Board also recommended that the Federal Railroad Administration make regulatory changes to enhance the collection of information about rail cracks and derailments caused by bond wire attachments. The Board further recommended that the Railroad Engineering and Maintenance- of-Way Association update its manuals to take account of what had been learned in the Tamaroa investigation.
A synopsis of the accident investigation report, including the findings, probable cause and safety recommendations can be found on the “Publications” page of the Board’s Web site, www.ntsb.gov.
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