In a public meeting today, the National Transportation Safety Board determined that Canadian Pacific Railway's ineffective inspection and maintenance program caused the January 18, 2002 derailment of a Canadian Pacific train about one-half mile west of Minot, North Dakota. Five tank cars carrying anhydrous ammonia, a poisonous gas, ruptured and released their entire contents creating a poisonous vapor plume that covered the accident site and surrounding area.
"This accident demonstrates how critical it is that we never relax our commitment to safety, "said NTSB Chairman Ellen Engleman- Conners. "We must make use of every safety tool, and every piece of technology that helps us identify and eliminate risks in our transportation system."
The Safety Board found that Canadian Pacific's rail inspection procedures were inadequate, which allowed undetected cracks in joint bars to grow to critical size and completely fracture. The Canadian Pacific Railway had discontinued ultrasonic testing of joint bars, before the accident, a procedure that could have identified the cracks before they failed. The Board also criticized the Federal Railroad Administration (FRA) for not requiring adequate inspections and testing of joint bars in continuous welded rail and recommended that on-the-ground inspections and nondestructive testing be required for continuous welded rail.
Contributing to the severity of the accident was the failure of five tank cars and the instantaneous release 146,000 gallons of anhydrous ammonia. Over several days a total of almost 221,000 gallons of the gas were released. One resident was killed from exposure to the gas. Over 300 people were injured and the vapor plume covered an area that affected about 11,600 residents.
The five tank cars that catastrophically ruptured were manufactured before 1989 with non-normalized steel. In low temperatures steel becomes brittle and fractures more easily. "Normalizing" is a heat treatment process that lowers the temperature at which steel will become brittle, making the cars more resistant to fractures. All tank cars manufactured after 1989 are required to use normalized steel. Outside temperatures at the time of the derailment were about -6 degrees Fahrenheit and examination of the five failed tank cars revealed that the brittleness of the non-normalized steel contributed to the cars' complete fracture and separation.
The Board recommended the FRA conduct studies to determine the impact resistance of pressure tank cars manufactures before 1989 and, using the information, establish a program to rank tank cars constructed before 1989 according to their risk of catastrophic fracture and attempt to mitigate the risk.
Chairman Engleman-Conners noted that 35 investigators had spent about 12,700 total hours working on the 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. The complete report will be available in about six weeks.