Two years ago this month, an oil pipeline burst in Michigan. It didn't get much notice because everyone was focused on the massive BP oil spill in the Gulf of Mexico. But like the BP spill, that Michigan spill was also one of America's costliest. So far, more than $800 million, and it's still being cleaned up. Today, the National Transportation Safety Board says the spill could and should have been avoided. Here's NPR's Elizabeth Shogren.

ELIZABETH SHOGREN, BYLINE: On the evening of July 25, 2010, alarms started going off in a control room as soon as the pipeline burst open. But three shifts of pipeline operators misinterpreted those signals. Deborah Hersman chairs the NTSB, which was charged with figuring out what caused the catastrophic spill.

DEBORAH HERSMAN: It wasn't until late Monday morning, 17 hours and 19 minutes after the rupture, that a worker from a local gas utility found the spill and notified the Enbridge control center.

SHOGREN: Only then did Enbridge, the Canadian company that owns the pipeline, turn off the flow of the pipeline and sent people to investigate. By then, more than 800,000 gallons of crude oil had gushed into nearby wetlands and a creek in Western Michigan.

NTSB Chair Hersman says even when Enbridge detected the spill, the company did such a bad job of trying to contain it that the heavy tar sands oil the pipeline carried spread through 38 miles of the Kalamazoo River.

HERSMAN: When we were examining Enbridge's poor handling their response to this rupture, you can't help but think about the Keystone Kops. Why didn't they recognize what was happening, and what took so long?

SHOGREN: NTSB investigators determined that the six-foot gash in the pipe was caused by a flaw in the outside lining which allowed the pipe to crack and corrode. Now, in 2005, Enbridge actually had learned that this section of pipe was cracked and corroding.

HERSMAN: Yet for five years, they did nothing to address the corrosion or the cracking at the rupture site. And the problem festered.

SHOGREN: That same 2005 internal report pointed to 15,000 defects in the 40-year-old pipeline. And Enbridge decided not to dig up this area to inspect it. Enbridge did report those defects to the agency charged with pipeline safety, the Pipeline and Hazardous Safety Materials Safety Administration. But according to investigators, that agency is poorly staffed and its regulations are weak.

Hersman says the pipeline safety agency should have the power to make sure companies aggressively inspect their pipelines and replace them before they get so decrepit.

HERSMAN: Delegating too much authority to the regulated to assess their own system risks and correct them is tantamount to the fox guarding the hen house.

SHOGREN: After the NTSB meeting today, Enbridge officials said they were not prepared to give an interview. But the company said in a press release that it has already improved its practices, and it is now reviewing the NTSB report to see if it needs to make more changes.

Hersman says that Enbridge and other pipeline companies and regulators have failed to listen to the NTSB recommendations in the past. And she fears that more spills will be on the way, unless the whole pipeline industry starts listening and make safety as big a goal as profits. Elizabeth Shogren, NPR News, Washington.

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