The Ontario Fire Marshall's Office has determined the cause of the Kenwick Place high-rise fire downtown was accidental.
Fire Investigation Coordinator Rick Derstroff told a news conference at the George St. site Wednesday morning that the fire originated in the building's electrical services room on the third floor and was sparked by the failure of a heating cable.
Derstroff says they're still investigating what caused the smoke to migrate throughout the 18-storey building.
Sarnia Fire Chief John Kingyens says it took about six hours to complete a planned evacuation Sunday.
He says firefighters were faced with tough conditions evacuating residents of the 242-unit downtown building despite pitch black stair cases and no working elevators.
Damage to the building is still being assessed and no date has been set for when residents can return.
The residential area has been released to the building owner and restoration and clean-up began Tuesday evening.
There is still no update on injuries.
Fire officials say 16 people were taken to hospital and two were initially said to be in critical condition.
