An "active" smoke test on the weekend near the Confederation Line's maintenance and storage facility was needed to complete safety work on the LRT line, Ottawa's transit agency says.

Saturday's test at the Belfast Yard tunnel site was run in co-operation with the city's police and fire departments, and monitored by staff from OC Transpo and the Rideau Transit Group (RTG), the consortium building the $2.1-billion line.

The maintenance tunnel, which runs from the maintenance yard to the Confederation main line, is naturally ventilated.

The smoke was required to test the efficiency of that ventilation, according to OC Transpo's director of rail operations Michael Morgan.

"[We] created a smoke condition in the tunnel to validate the performance of the tunnel to dissipate smoke if there was to be [an incident] in that particular tunnel," said Morgan.

Previous test led to injuries

A test on the main downtown tunnel on Nov. 21, 2018, ended with four OC Transpo LRT drivers being transported to hospital after they were exposed to what Morgan called "non-toxic" cold smoke.

The drivers suffered no long-term injuries, Morgan said, and RTG and OC Transpo worked to adjust policies to ensure that it wouldn't happen again.

The downtown tunnel is actively ventilated with turbofans, Morgan said

He called this weekend's test a "final check in the box to say that the system is ready for service."

RTG will now submit a final engineering report to OC Transpo, which will review it as part of their safety checks as RTG prepares to hand control of the Confederation Line over to the city.

The current plan is for the city to take over the line from RTG before July 1st, but previous handover dates were delayed.