Final report on 2011 Minneapolis gas explosion - KMSP-TV

19 months later, the Minnesota Office of Pipeline Safety has released its final report on the March 17, 2011 gas pipeline explosion at 60th Street and Nicollet Avenue in south Minneapolis.

Investigators are blaming the blast on joints that became uncoupled and shifted under massive pressure. In addition to pinpointing the cause of the gas leak and explosion, the report shows a need to potentially replace the majority of a pipeline system that runs under several neighborhoods across Minneapolis.

No one was injured in the explosion that sent a fireball over Highway 62, shutting down roads and stopping traffic for nearly three hours that morning.

The Pipeline Safety report says the steel pipeline failed at two points, causing the leak and explosion. The explosion damaged underground facilities, roads, cars and above-ground buildings within a 350 ft. radius on the 60th and Nicollet intersection.

The report says a leak on the same pipeline was detected in December 2011. At that time, Pipeline Safety directed CenterPoint Energy to perform daily leak surveys above the pipelines until all suspect joints had been fixed.

Following the March 17 explosion, CenterPoint energy found other high-risk locations and has since initiated a program to weld Dresser compression sleeves over mechanical joints. CenterPoint is also evaluating the need to replace a majority of the "Beltline" transmission pipeline.

Beltline upgrade project information has been posted at http://www.centerpointenergy.com/assets/promo/beltline/faqs/

SUMMARY OF MARCH 17 PIPELINE FAILURE

The 20-inch diameter, steel natural gas transmission pipeline failed at two Dresser Style 38 mechanical couplings that joined an "Electrostop" isolator fitting to the 20-inch pipeline. The mechanical couplings separated from the pipeline on either side of the 4-foot long "Electrostop" isolator fitting. The couplings failed in two locations; one location was directly attached to a straight length of pipe and the other location was on a 45-degree pipe bend welded to an adjacent 45-degree pipe bend. Two more 45-degree bends were located within 8 feet west of the failed joint.

PRE‐INCIDENT EVENTS

January 5, 2009
Gas odor reported by Cub Foods employee

November 21, 2010
Gas odor reported by Cub Foods employee

March 17, 2011 (morning prior to incident)
Gas odor detected by Cub Foods employee outside in parking lot. Gas odor also reported by Mr. Emmett DySart (contract employee for Auto Rescue, interviewed by MNOPS and news media.)

INCIDENT TIMELINE

March 17, 2011, 8:35 a.m.
Natural gas leaks from 20‐inch steel transmission pipeline and ignites

March 17, 2011, 8:55 a.m.
Duty Officer notified of incident

March 17, 2011, 9 a.m.
MNOPS notified of incident. Evacuation of 6‐block radius and traffic re‐routed

March 17, 2011, 9:49 a.m.
Gas off and flames extinguished

March 17, 2011, 9:50 a.m.
MNOPS arrives on site

March 17, 2011, 11:45 a.m.
Evacuation lifted and roads re‐opened

CenterPoint says they weren't aware of specific problems in the area prior to the explosion, but according the report as far back as January 2009 an employee at the nearby Cub foods reported smelling a gas odor.

A gas odor was reported again the next year, but a CenterPoint spokesperson says crews checked the pipeline and no leaks were detected in that area. The utility also stressed odors don't necessary mean people are smelling gas -- the smell could be from the sewer or something else. But the next time someone smelled a gas odor was March 17, 2011 -- the day of the explosion.

CenterPoint says they follow all rules and guidelines and go above those set for them by regulators.