Four train operators were taken to hospital after a ventilation test in Ottawa's LRT tunnel went wrong.

It happened below Queen Street in Lyon Station, just after 10:00 p.m. on November 21.

“When they (train operators) arrived at Lyon station, they noticed people with gas masks on and smoke started entering the train,” says Transit Union President Clint Crabtree.

The incident happened after the four train operators were told to bring two trains to Lyon station and park them. That's when smoke bombs were lit in the tunnel, part of a Rideau Transit Group and OC Transpo plan to test the tunnel’s ventilation system.

RTG, OC Transpo and emergency workers on the platform were prepared, wearing protective gear. The drivers had nothing. Smoke started filling one of the trains. Crabtree says the incident was caught on camera.

“(The operators) haven't a clue of what's going on,” says Crabtree. “They haven’t been notified, there's been no communication given to them.”

“You can see people standing outside the cabin on the platform with gas masks on and my members are facing this and can you imagine the fear in them right away when you see someone on a platform with a gas mask on and you don't have one on yourself,” says Crabtree.

Sources say operators started showing symptoms from the smoke, including sore throats and itchy watery eyes. The four were later assessed by paramedics and taken by ambulance to hospital.

Sources tell CTV News all four exhibited elevated levels of carbon monoxide, were put on oxygen and had chest x-rays and blood samples taken. Crabtree says they spent the night in hospital,

“The smoke that is used in these tests is artificial smoke there's nothing toxic associated with that,” says John Manconi, City of Ottawa Transit Services General Manager. “They were taken to the hospital as a precaution, they were all fine.”

Manconi admits there was a communication breakdown.

“The operators should have been taken out of that vehicle and they weren't,” he says.

Ontario’s Ministry of Labour says inspectors were notified, visited the scene and did not issue any orders. The investigation is now complete.

Sean McKenny, President of the Ottawa and District Labour Council has concerns.

“To have four operators in the tunnel without protective equipment is nonsense,” he says.

Manconi contacted McKenny hours after the incident. Still, McKenny says he continues to have safety concerns with this LRT project.

“All of the things that we've heard from the get go is it's preventable and our city says the safety is the most important and yet it sure doesn't seem to be that way more times than not," he says.

Manconi says his job is to report these incidents to both provincial and federal labour investigators, which he did. He says since the incident, new procedures have been put in place to ensure train operators are removed from the trains before any testing begins.