News

Mar 11, 2023

Urban sprawl on wooded lands presents unique challenges when fires spread: experts

Robert Gray, a wildland fire ecologist in British Columbia, said whether a fire

Robert Gray, a wildland fire ecologist in British Columbia, said whether a fire is in an urban or wildland setting, one of the first things firefighters do is establish a containment zone.

In forested areas, he said, firefighters put down a fire break around the boundaries of the blaze to keep it from spreading further. This is usually done by bulldozing up mineral soil or pouring a combination of water and retardant out of a helicopter, he said.

"All you can do to stop the fires is rob it of energy, of fuel," he said.

While in forested land the interior of a fire is often allowed to burn itself out, in an urban setting the main aim is to stop it from spreading to structures, Gray said.

"You don't want what's called an urban conflagration, which is multiple houses burning at once," he said.

Dave Steeves, a forest resources technician with Nova Scotia's Department of Natural Resources, said firefighters are following a direct and indirect approach to attack the Halifax wildfire.

"The direct attack … is where we’re spraying water directly on a fire," he told reporters. "Indirect attack … is where we are removing vegetation from an approaching fire." The purpose of removing vegetation and creating a perimeter is to starve the fire of fuel, he told reporters this week.

"If the intensity levels are low enough, when it burns up to that break, it will have nowhere to go and it will it will snuff itself out."

He noted that while traditional firefighting in forests would first involve establishing a containment line, that approach wasn't well-suited to the Halifax fire.

"This situation was so different with the amount of structures that were involved, that it was difficult to take a traditional approach to it," he said. "We had to focus on the structures of value first, before we could actually work on the containment."

Blazes that experts have said are examples of interface fires include the Fort McMurray and Slave Lake, Alta., infernos where homes were built on the edge of woods. The 2011 Slave Lake fire destroyed more than 400 homes and the 2016 Fort McMurray wildfire destroyed more than 2,400.

Gray said one of the most important priorities when confronting an interface fire is to prevent as many structures as possible from burning down, while watching out for the many threats firefighters face in urban areas such as downed power lines, vehicles and all that goes into making everyday life.

"Homes burn differently than the woods do," he said. "It can be quite hazardous for firefighters." The chemicals in the air are different because they involve compounds released from the combustion of manufactured goods, he said.

"We don't wear breathing apparatus on wildland fires, although we may have to in the future," Gray said. "We’re dealing with very different smoke and smoke constituents. It's the makeup of the smoke that can be very, very dangerous in an urban setting, especially if there's high winds, and there's lots of structures involved at one time."

Collet said the hazards are the biggest difference between fighting wildfires on forested land versus in urban areas.

Damaged homes that can fall on firefighters, vehicles that explode, downed power lines and weakened trees are just some of the hazards firefighters have to navigate in urban settings, he said.

"The wilderness is a little bit different, because it's mostly just trees," Collet said. "What we’re doing is we anchor from a safe place, and we start fighting the fire — working that way. There may be a little more risk when you’re trying to save somebody's house. But again, the training is different. And the structure firefighting is done by fire departments."

Training for firefighters in urban areas is different compared with those in forested areas, Gray said, although some rural communities offer cross-training.

"Communities that have both kinds of fires, they do cross-training," he said. "They’re taught to deal with both structure fire and wildfires. There's actually a course for wildland firefighters working in the interface. It deals with things like hazardous materials and electricity and things like that."

This report by The Canadian Press was first published June 2, 2023.

Hina Alam, The Canadian Press