A 16-storey apartment building was evacuated in the pre-dawn hours on Saturday because of a carbon monoxide leak.
People were allowed back into their homes at 225 Markham Rd. at about 4:30 a.m. after the building was ventilated and the problem was isolated.
A few people were treated for minor injuries at the scene.
The Technical Standards and Safety Authority is looking into what caused the leak but fire officials believe work on the boiler might be to blame.
Toronto Fire Services said carbon monoxide detectors in the building prevented this from becoming a serious incident.