Report ID's Cause of Windom Pipeline Explosion

State investigators believe they know what caused a large explosion and fire in Windom on St. Patrick's Day last year, according to WCCO-TV. Poor construction, the station reports, was at fault, and had led to several leaks before the spectacular March 17, 2011 conflagration.

In the middle of the morning commute on March 17, 2011, an underground pipeline ruptured near the intersection of Nicollet Avenue South and 60th Street. Burning natural gas surged skyward in a towering inferno that could be seen from many blocks away. 

Neighborhood resident Tom Meckey was driving on 54th Street when the explosion happened.

"You heard a big boom and I looked to my right to see where it was coming from and you just saw this huge plume of flames in the sky," Meckey told Patch the day of the explosion.  "From 58th and Nicollet I got out of my car to take a picture and you could just feel the heat coming off of it. It was pretty intense."

See photos of the explosion above.

The blaze torched several cars in the Cub Foods parking lot, melted nearby traffic signals and signs, and blew open a gaping crater over 15 feet wide.

Minneapolis and Richfield emergency crews evacuated a six-block radius around the blaze, and closed down parts of I-35W. The fire burned for several hours until Centerpoint Energy crews were able to shut off the flow of gas in the pipeline, starving the fire of fuel. 

As it turns out, that wasn't the only time the pipeline had spewed gas, according to the investigators' report. Later in 2011, the same pipe sprung a leak, causing regulators to order Centerpoint search for leaks every day. 

The Windom section of the pipeline was particularly vulnerable—it wasn't designed to handle the weight of soil and passing cars pressing down on it, and efforts to shore up the pipeline were incorrectly carried out, the report says.