Here’s what to know about the Thorncliffe Park highrise fire that displaced hundreds

TORONTO — A residential apartment fire that displaced hundreds of people from two buildings in Toronto on Thursday was still burning slowly four days on, fire officials said Monday.

Firefighters said the smouldering fire was burning through insulation trapped in the concrete walls between two Thorncliffe Park highrise towers.

Fire officials wouldn’t comment on the cause of the fire as they continue to fight it and investigate its origins.

Here’s what to know.

What situation are firefighters facing?

Toronto fire Chief Jim Jessop said the fire is burning the combustible particle board that was placed in the expansion joint between the two buildings, and crews are not able to access that material to stop the fire.

“That is causing us the problem, and access to getting to this is next to impossible for our crews. And we have been trying everything,” he said.

“If you can imagine a cigar burning slowly up and up without visible flames, this is what my staff have been dealing with since Thursday afternoon at 1:30, with no way to access it.”

Jessop said he has not seen a complex fire like this in his 30 years of service with Toronto fire.

“I’ve obviously been meeting with our senior operations commanders that have been with Toronto Fire Services for 40 years. They have never seen something as complex as this,” he said.

“We were up on the roof this morning, and there was visible smoke still coming out. And you’re talking after four days of our staff continuously fighting this fire, literally, both exteriorly from the roof and into units right now on the interior side.”

Why is the fire so difficult to put out?

Mark Green, a civil engineering professor at Queen’s University, said part of the challenge with smouldering fires is that they burn at a “very slow rate” with little oxygen present.

It’s “quite unusual” for smouldering fires to grow into something with visible flames when trapped in between the walls, said Green. The fire will slowly burn through material before moving onto the next part of the burn.

He said fires are especially tricky to extinguish when they are trapped inside walls. Not only are they hard to access, but traditional firefighting tools don’t always work under those circumstances — the fire can’t simply be doused or stamped out.

“You can’t really cool it down effectively and you can’t smother it.”

Maged Youssef, a civil engineering professor at Western University, said in an email these types of fires are known as “stubborn and labour-intensive.”

“Because insulation resists heat loss and limits airflow, it creates the ideal conditions for a long-lasting, low-visibility fire that’s difficult to locate, suppress and confirm as extinguished,” he said.

He added the fires “often require firefighters to open walls and physically remove smouldering material to extinguish them fully.”

What happens next?

Jessop said a team of engineers from Toronto Fire Services, Toronto Building and the building’s owners are working together to try to come up with ideas on how to quickly extinguish the fire while the investigation into the origin, cause and circumstances of the fire continues.

Youssef said the type of fire they are fighting often requires firefighters to “open walls and physically remove smouldering material to extinguish them fully.”

No matter how they choose to continue, Green said firefighters will need to contend with the risks that come from exposure to carbon monoxide and other gases released from burning materials.

What about the displaced residents?

Close to 400 units had to be evacuated on Thursday when the fire broke out and carbon monoxide levels spiked.

On Monday, evacuees from two buildings were still without a timeline for a return to their homes.

Joanna Beaven, the executive director of Toronto emergency management, said a total of 141 households that represent 293 people are receiving support from the Canadian Red Cross.

She said the displaced people who are receiving help are staying in 117 hotel rooms.

Beaven said the city has extended the emergency support for evacuated residents including hotel rooms, food, hygiene products and transportation until Thursday.

This report by The Canadian Press was first published Dec. 1, 2025.

Cassidy McMackon and Maan Alhmidi, The Canadian Press