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A view of some of the fire damage inside the refinery. (Submitted to CBC)

Investigators say a corroded pipe that failed and leaked fuel was the cause of a major fire and explosion at Regina's Co-op Refinery last fall.

No one was killed in the Oct. 6, 2011 accident, but 36 people were injured, about $100 million worth of damage was done and the Co-op was forced to shut down some of its production for months.

According to the results of the investigation by the City of Regina and three provincial agencies, the blast, which happened in an area that processes diesel that was built in 1961, was an accident.

The failure resulted in a 19-centimetre-long rupture in the pipe, releasing diesel and causing the explosion and fire.

Investigators said one factor was "refining process changes" introduced in 2008 that caused a "higher-than-usual corrosion rate."

Trying to deal with the extra corrosion, the company later replaced a section of pipe.

"Our inspection protocols and judgment led us to believe we had indentified all problem areas and made the necessary pipe replacement," said Scott Banda, CEO of Federated Co-operatives Ltd., which owns the refinery. "Unfortunately, that was not the case."

At the scene, investigators found the section of pipe that failed had metal that was thinner than other pipes in the area.

Investigators believe static electricity might have provided the spark that started the fire.

The fire and explosion covered an area 30 metres by 45 metres.

Since it happened, all piping in the damaged area has been replaced. Some workers have not returned to the site.

The Co-op Refinery complex is one of the biggest industrial operations in Saskatchewan, with a processing capacity of 100,000 barrels per day.

"I'm terribly sorry for what happened and if we could change the events of the day we would," Banda said. "But it happened and any time there are injuries, that's a terrible outcome and I'm terribly sorry for that."

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The fire at Regina's Co-op Refinery on Oct. 6, 2011, injured 36 people. (Dani Mario/CBC)