REGINA - Investigators are trying to determine how and why a rail car full of asphalt rolled away from an oil refinery into a Regina neighbourhood this week.

Andrew Swenson, a spokesman for the Co-op Refinery Complex, says no one was hurt and no material from the rail car spilled late Tuesday.

The runaway rail car travelled about four kilometres through the city, crossing a number of streets, along tracks owned by Canadian National Railway (TSX:CNR).

Both the City of Regina and Regina Fire and Protective Services failed to receive notification of the incident. Mayor Michael Fougere said city staff didn't hear about it until Friday morning.

“We were not notified, the police service was not notified, in fact we found out through media reports this morning, so we’re quite concerned about that.”

Fire Chief Ernie Polsom also wants to know why they were left out of the loop.

“The transportation regulatory agencies will be doing an investigation. We are insisting on being a part of that, because there is clearly a public safety issue that affects Regina residents.”

Swenson said the rail car was being handled by Cando Rail Services, a subcontractor employed by the complex.

"We have suspended their contract and they won't be conducting work at the refinery until the investigation is finalized and we are able to review the results," he said Friday.

Cando said its employees saw the rail car move, took action to bring it under control and then reported it.

The Manitoba-based company said it has already been determined that the rail car was not properly secured.

"The investigation is looking at a number of possible causes including human error," the company said in a statement.

Cando said it supplies specialized railway support services to industry and the rail sector at 18 industrial sites across Canada.

CN said it has stopped Cando crews from operating on its rail network pending a review of the company's operating procedures and safety practices.

The Transportation Safety Board said it was gathering information Friday to determine whether to begin a formal investigation.

Board investigator Jerry Berriault said Cando staff were involved in switching cars at the refinery when the car started to roll down a slight incline.

"It was sitting by itself and left the plant and there is a slight downhill grade from that plant toward Regina, so that is what propelled the car on its own."

Berriault said the safety board will look at how the rail car was secured and if there were mechanical issues.

Rail lines usually have a mechanism called a derail to prevent cars from rolling, but crews usually remove the device during switching operations when they are moving cars on the tracks, he said.

The Co-op Refinery Complex is owned by Federated Co-operatives Ltd.

— By John Cotter in Edmonton, with files from CKRM

News from © The Canadian Press, 2016