The recommendation is contained in the board's final report of an investigation into a release of hazardous materials and fire that killed three workers at the ATOFINA Chemicals facility in Riverview, Mich.
At 3:45 a.m. on July 14, 2001, a pipe attached to a fitting on the unloading line of a railroad tank car fractured and separated, causing the release of methyl mercaptan, a poisonous and flammable gas. About 25 minutes later, the methyl mercaptan ignited, engulfing the tank car in flames and sending a fireball about 200 feet into the air. The fire was extinguished about 9:30 a.m. Three plant employees were killed in the accident. About 2,000 residents were evacuated from their homes for about 10 hours.
The NTSB believes the probable cause of the accident was a fractured cargo transfer pipe that resulted from the failure of ATOFINA to adequately inspect and maintain its cargo transfer equipment and inadequate federal oversight of unloading operations involving hazardous materials.
ATOFINA's reliance on a tank car excess flow valve to close off leaks (the device was not appropriate for this type of leak) and the company's failure to require employees to wear appropriate safety equipment contributed to the accident, according to the board. The workmen were not wearing self-contained breathing apparatus (SCBA) and were instructed to detect by odor the release of methyl mercaptan.
In addition, the only way to shut off the flowing product in the event of a leak like this was to use a manual valve on top of the tank car - no remote cutoff switch was installed.
"By its very nature, the work these employees performed around chemicals was extremely hazardous," NTSB Chairman Marion Blakey said. "The lack of some basic safety precautions in this operation was a fundamental flaw, and proved tragic for the three men who lost their lives last July."
The pipe that failed was weakened by erosion and corrosion that occurred over a protracted period of time. Visual inspections failed to detect the deteriorating condition of the pipe.
The NTSB notes that since the accident, ATOFINA has made a number of changes to its plant procedures and equipment to address problems identified during this investigation. The company now requires that the cargo unloading apparatus, including the integral piping, be removed from service every two years and undergo non-destructive testing to ensure that it is still safe. Additionally, ATOFINA has redesigned the unloading apparatus. Operators are now required to wear SCBAs when working on the methyl mercaptan tank cars, and they are required to carry an escape hood with an emergency air supply when in the area of the tank cars. In addition, operators now perform leak tests on the unloading apparatus before opening the valve to the tank car.
In the report, the NTSB claims that current federal oversight of loading/unloading operations is deficient. For example, Federal Railroad Administration (FRA) regulations cover the setting of tank car brakes, the chocking of wheels and other such matters, but they do not address the inspection, maintenance and support of cargo transfer fittings, leak test procedures for fittings or the use of personal protection equipment by operators. The board therefore recommended that DOT, with the assistance of the Environmental Protection Agency and the Occupational Safety and Health Administration, promulgate new rules to address these deficiencies.
The NTSB also recommended that the FRA warn companies involved in tank car loading and unloading operations that tank car excess flow valves cannot be relied upon to stop leaks that occur during those operations.
A summary of the board's report is available on the NTSB's Web site at www.ntsb.gov under "Publications". The full report will be available on the Web site in about a month. Printed copies may be purchased from the National Technical Information Service at 1-800-533-NTIS.