Poor ventilation caused carbon monoxide to build up in a Winnipeg hotel rather than make its way outside the building, officials said Wednesday.

The gas leak at the Super 8 hotel resulted in 46 people being taken to hospital earlier this week, including seven hotel employees.

Chuck Steele, Manitoba Hydro's director of engineering and construction, told a press conference that "inadequate ventilation related to gas-fired appliances" – namely, a boiler – caused the CO buildup. More tests will take place to determine why the gas was not being properly vented.

Firefighters reported carbon monoxide levels as high as 385 parts per million. Buildings in Winnipeg are typically evacuated when levels of 12 parts per million or more are detected.

The hotel was found to be complying with all legally required carbon monoxide protections during its last inspection, which took place in 2017.

Deputy Winnipeg fire commissioner Candace Russell Summers said Wednesday that there were carbon monoxide detectors in the building, but called it "premature to comment with certainty about the type or the number of detectors that were found, and whether or not they meet regulatory requirements."