Four days before a huge sinkhole opened up on Rideau Street as workers excavated the final 50 metres of the underground light rail line below, fire broke out in another section of the downtown tunnel.

Nobody was hurt in either incident, but some workers have contacted CBC News to say they're concerned about health and safety on the project.

"There was a fire and there were no hoses to put it out," said one former worker, who asked not to be named. Information provided by workers has been verified by CBC News.

In a statement, Rideau Transit Group confirmed the June 4 fire at Parliament station at O'Connor and Queen streets, the next stop west of Rideau on the Confederation Line.

"Fire was contained and extinguished by the crew. Once conditions were safe, workers resumed their work," said RTG, the consortium of companies building the Confederation Line.

Ministry told of fire 2 days later

According to RTG, at any given time up to 875 employees, including subcontractors, are working on the multi-billion dollar project.

The Ministry of Labour told CBC it was notified about the fire two days later, on June 6.

"The ministry has not conducted a visit in response to this notification. The constructor has informed the ministry of precautions taken to prevent a re-occurrence," according to a statement.

But that's not good enough for the former worker who contacted CBC.

After two years working on the LRT project, he said he's found another job because of his concerns over his health and safety. He and another worker also complained to CBC about high levels of carbon monoxide and dust in the tunnel.

Surprise inspections

The ministry said it has conducted 29 visits to the Ottawa LRT project, 26 of which were unannounced inspections to check for compliance.

We've got a lot of confidence in the safety management program that our contractor has. - Peter Lauch, Rideau Transit Group

The ministry confirmed it has received "several complaints regarding dust since the onset of the project. Orders were issued and have been complied with." The ministry also confirmed it has received one complaint about carbon monoxide in the tunnel.

When it comes to air quality, RTG said air samples are taken three times a day in the tunnel. It also said safety masks are required and air "scrubbers" help clean the air.

"There have been no reports to the safety committee in this regard," RTG said.

Fewer injuries than industry average

In fact, RTG maintains that to date, more than three million hours have been worked on the project with only "10 lost time injuries" — a method used within the industry to calculate the relative frequency of workplace injuries — a rate the consortium said is better than average for heavy construction projects in Ontario.

Asked about the complaints from workers, RTG technical manager Peter Lauch insisted the tunnel is a safe workplace.

"I go into the tunnel quite often. I'm quite comfortable going in there, but I go in as a tourist. I don't spend eight to 12 hours a day there," said Lauch. "We've got a lot of confidence in the safety management program that our contractor has."

Contact Julie Ireton at julie.ireton@cbc.ca or (613) 288-6478