Why several cars in a slow-moving train carrying petroleum crude oil derailed under the Magnolia Bridge in Interbay on Thursday remains a mystery.
"The cause is still under investigation," Courtney Wallace, a spokesperson for BNSF Railway Co. said in an email on Friday. Three tank cars, each filled with nearly 30,000 gallons of flammable crude oil, jumped the tracks, as did a hopper full of sand and a locomotive. At the time of the derailment the train was creeping along at 5 mph.
Robert W. Halstead is president of IronWood Technologies, Inc., a company that reconstructs railroad accidents. He is not involved in the accident investigation and would not speculate on the cause of Thursday's derailment. But he did mention a variety of factors that could be to blame in such an accident, including track defects, equipment failures or human error.
For example, the level between the two rails of the train track might have been uneven, a wheel or axle may have broken on one of the cars, or the front locomotive could have slowed while the one in the rear maintained its speed or accelerated.
Halstead added that the locomotives would have been equipped with event recorders and video cameras and that the train engineer would also likely be interviewed to "find out what he was doing at the moment of the derailment."
The incident took place around 2 a.m. on Thursday. According to Wallace, the track where the mishap occurred was reopened around 5:45 a.m. on Friday.
BNSF will transfer the oil out of two of the derailed tank cars next week, Wallace said. The third car sustained only minor damage and will not be emptied.
The train included 100 tankers filled with crude oil from North Dakota's Bakken oil fields. It was headed north to a refinery in Anacortes.
The U.S. Department of Transportation has indicated that Bakken oil may be more volatile than other types of crude. A number of fiery wrecks and derailments involving trains transporting petroleum crude oil have raised safety concerns.
DOT released a set of draft rules on Wednesday that include new restrictions and requirements for rail shipments of petroleum crude oil.
"Crude oil was not considered a serious, dangerous chemical until they started shipping it in unit trains," Fred Millar, an independent rail consultant, told Crosscut recently. A unit train is one in which all the cars are carrying a single commodity.
Tank cars carrying Hazmat Class 3 Flammable Liquids (a category that includes crude oil) roll past a rail crossing at Lander Street in Sodo. Photo: Bill Lucia
BNSF sends between eight and 13 of those trains through King County each week, according to information the railroad recently released to the Washington Military Department.
None of the tank cars that derailed on Thursday was breached and no oil was spilled, according to the railroad and the Seattle Fire Department.
A BNSF spokesperson said earlier this year that trains carrying crude oil do not exceed 25 mph when passing through the city limits.
Federal Railroad Administration records show that between January 2013 and April 2014 BNSF reported 18 incidents in Washington state involving train cars or locomotives that derailed.