Emergency crews have stabilized a train that got trapped on the Bonnybrook Bridge after a structural failure and the Transportation Safety Board of Canada is now investigating.

A CP Rail train got stuck on the bridge over the Bow River on Thursday morning at about 3:45 a.m. after it partially collapsed.

Six cars derailed and five more, ull of petrolium distillate, were trapped on the bridge.

Mayor Naheed Nenshi spoke out on the incident on Thursday morning and had some harsh words for CPR, the company in charge of the track and the train carrying the dangerous material.

"This, of course, has impacted the City of Calgary enormously. I know that a number of questions will arise from that," Nenshi told a briefing at 11 a.m.

According to city engineers, the Bonnybrook Bridge is an old bridge - it dates back to the foundation of CP. "It was probably authorized by Sir John A. Macdonald," Nenshi said.

However, beyond that, they don't know much about it because the CP bridges in Canada are exempt from municipal regulation. "It is the only private business operating within the city's boundary that the municipality cannot regulate."

Nenshi insisted that the city's own bridges are safe and they've been inspected three times since the flooding.

"Our bridges are all built in the same way - they're all built eight feet into the bedrock for the largest part. This bridge was not built into the bedrock - which we just learned today - and we continually remediate and reinforce our bridges," Nenshi said.

The mayor hammered the point home by mentioning the Centre Street bridge, a 100-year-old bridge that he says is 'strong, stable, and safe'. "It made it through this situation very very well."

Nenshi says that there needs to be a serious conversation over safety. "This a private business and other private businesses are subject to regulation."

He adds that there are a lot of questions into the handling of this issue with the Bonnybrook Bridge. "Our number one priority is safety, but once this crisis is over, I'm going to be looking for a lot of answers from a lot of people.

"I'll be very blunt. I'll probably get in trouble for saying this - we've seen a lot of people lose their jobs at CP over the last year. How many bridge inspectors did they fire? These are the questions that we need to understand much much better after we assure the safety of the water and the safety of everyone who is there."

Ed Greenberg, a spokesperson with Canadian Pacific, says he isn't sure what the caused the problem.  According to his information, the bridge checked out on Saturday after last week's flooding and has been used several times since.

The rail was also inspected by a professional inspector on Monday and no problems were found.

The fire department brought in a stabilization train to ensure the trapped train does not end up floating down the river.

“A train loaded with rocks and grain cars. And we’re using that, coupled to the six damaged cars that are on the bridge, to secure it and use it as an anchor. We then also went through and then CP crews with firefighters, we tethered each individual rail car to that stabilization train,” said Acting Fire Chief, Ken Uzeloc.

Crews were hoisted into position using a vehicle with a bucket at the end of a long arm to attach the tethers and install hoses so they did not have to go on the damaged bridge.

Uzeloc says the one section of the bridge is partially in the water but has not moved in the last three hours.

He says they believe the bridge is relatively stable right now but they will take their time to ensure everyone remains safe.

“We wanna make sure we are doing things as safely as possible for everyone involved and that includes the environment because the last thing we want is a bunch of petroleum product into the river,” said Uzeloc.

Crews are now in the process of setting up a pumping station.

“We have two rail cars hooked up with hoses and pumps and we’re doing a third right now. As soon as that’s in place we will move the empty tank cars that are on the undamaged bridge in alignment and then start pumping the product out of the damaged cars into the undamaged cars,” said Uzeloc.

Uzeloc says they will make a decision on the best way to remove the cars from the damaged bridge as soon as the product is removed.

The Transportation Safety Board of Canada is now investigating the incident.

“We absolutely are investigating this accident. We’ll be looking for what happened and why it happened,” said Wendy Tadros, Transportation Safety Board of Canada Chair. “We’ll be looking for the cause of that accident. We’ll be conducting a full and independent investigation.”

Tadros says the TSB will also look into the inspections that were done on the bridge before trains went over it.

“We’re on the ground. We have two people out there at the moment. They’re going to be looking at the cars, they’re going to be downloading the data recorder that’s on the locomotive. They’re going to be interviewing the crew and they’re going to be getting the inspection records. Until we take a good hard look at those we won’t know what we’re dealing with,” said Tadros.

Crews have opened up Barlow and Deerfoot Trails for the evening rush hour.

The half-mile evacuation zone has been reduced to within 300 metres of the derailment.

Ogden Road remains closed north of 50 Avenue and 17 Street S.E.