Update: On Oct. 23, CenterPoint Energy responded to the state report, saying it respectfully disagrees.

MINNEAPOLIS (WCCO) – State investigators say design failures of a natural gas pipeline caused a massive explosion on Saint Patrick’s Day last year in southwest Minneapolis.

It happened that morning near 60th Street and Nicollet Avenue. The explosion rocked the neighborhood, and flames shot three stories in the air, over buildings and Interstate 35W.

“It blew up,” said a witness that March day. “Someone yelled, ‘Fire! Fire!’”

Residents evacuated, and emergency response teams sprang into action. A gas leak from a natural gas pipeline had ignited: A 20-inch steel pipeline had failed.

According to the Minnesota Office of Pipeline Safety, the pipeline’s inability to sustain external loads, like the weight of soil, roadway and traffic, was a factor in its failure. The report says that one or more steel straps welded over the pipe joints failed prior to the explosion.

Improper design and failure to install the joints, so they could sustain those load pressures, were contributing causes to the event.

About one year ago, another leak on the same pipeline was detected, so state officials ordered CenterPoint Energy to start surveying for leaks daily until the problems were corrected. That included a program where the energy company went back and welded parts of the pipeline in high-risk locations.

CenterPoint just got the report and is looking at replacing a majority of an 80-mile pipeline that serves Twin Cities neighborhoods.

“The system is safe,” said Jim Bartula, a company spokesperson. “Safety is our top priority. The system is under constant review. It is safe regardless of the location.”

In a statement released on Oct. 23, CenterPoint said it respectfully disagrees with the conclusions of state investigators. The energy company said a third- party industry expert, Crane Engineering, identified soil washout as the cause of the problem.

But despite the disagreement, CenterPoint said it will continue to work with the state as information on the incident continues to surface.