The exterior cladding used to retrofit London's Grenfell Tower has come under much scrutiny for the role it may have played in propagating the deadly fire.

But in Canada, strict rules on the use of cladding make it unlikely, though not impossible, that a similar tragedy could occur here, industry experts say.

At least 79 people are believed to have been killed in the 24-storey apartment building fire on June 14.

Cladding in and of itself is not a problem, and is used to retrofit the exteriors of highrise buildings in Canada and around the world.

But the cladding believed to have been used at Grenfell Tower — a polyethylene (PE) core aluminum composite panel — would have constituted a "major fail" in terms of safety, said John Straube, an associate professor of civil and environmental engineering at the University of Waterloo.

That combination of materials is considered highly combustible and the cause of significant fire problems in the last five years, said Straube.

Rigorous lab test

In Canada, exterior cladding must pass a rigorous lab test (known as the S134 "Fire Test of Exterior Wall Assemblies"). This is a standard set by the Underwriters Laboratories of Canada, an independent organization that does product safety testing, certification and inspection.

The cladding "must prove that it doesn't do what Grenfell Tower did," said Straube. "You could not use the PE-core panel in Canada on tall buildings, because it would not pass S134."

It may, however, be used on low-rise buildings that don't have too much of a fire propagation issue, he said.

(According to a recent Guardian report, the type of cladding believed to have been used on Grenfell — with a polyethylene filler — is not compliant with building regulations for taller buildings in the U.K. either.)

Cladding standards don't specify whether or not a certain material may be used. Instead, materials must meet performance requirements that show it has withstood fire tests and conditions, said Doug Perovic,a professor in University of Toronto's materials science and engineering department.

"[It would be] highly unlikely to find PE core cladding in code-compliant buildings in Canada," Perovic said.

The exterior cladding used to retrofit London's Grenfell Tower has come under scrutiny for the role it may have played in propagating the deadly fire. (Toby Melville/Reuters)

Perovic described the cladding like a sandwich, with most types containing a thin aluminum skin on the outside and a core with a polymer plastic foam-like material that acts as insulation, blocks wind and wards off moisture. It must also withstand fire from both the outside and within.

Combustible material must burn slowly

Combustible material may be used as part of exterior cladding in highrise buildings, but it must meet Canadian fire rating standards. That means that during a fire, the material burns at a rate that can be managed before it moves or spreads too fast and becomes out of control.

"To give a firefighter or responder an opportunity to arrive at a scene and put it out before things light up like a dry Christmas tree," Perovic said.

In the case of Grenfell Tower, other factors also may have fuelled the inferno, including the space between the cladding and the building structure, which some suggest led to a so-called chimney effect.

"You don't want that space to become a chimney for fire to race up hidden behind the cladding outside of the structure and rise up the building as well," Straube said.

One of the ways to stop the chimney effect is to ensure the insulation in that space can't burn by using stone wool insulation, he said. Or the cavities could be broken up at every floor with something that inhibits fire, like a piece of sheet metal.

"That apparently is missing in this building as well," Straube said.

The absence of a sprinkler system or fire alarms were also issues in the London building, and can play a large role in mitigating the effects of any fire regardless of whether cladding is involved.

The London fire also raised concerns about the refurbishment of old buildings in general, and how much that contributed to the scale of the blaze.

If done right, refurbishment can vastly extend the life and improve the quality of a building, whether by making it more energy efficient, stopping water and air leaks, fixing balconies and improving fire safety, said Straube.

'Makes them safer'

"There's literally no technical reason why we can't retrofit these buildings that not only [makes them] fire safe but generally makes them safer than they were," he said.

The cladding believed to have been used at Grenfell Tower — a polyethylene core aluminum composite panel — would have constituted a "major fail" in terms of safety, say some experts. (Tolga Akmen/AFP/Getty Images)

Straube said it's certainly plausible there are unscrupulous owners, contractors or professional designers out there who are ignoring codes.

But for all those players involved in the retrofitting to ignore such safeguards would be unlikely, Straube suggested.

Toon Dreessen, former president of the Ontario Association of Architects, said building officials need to be aware of construction that happens without a building permit and put a stop to it.

Apartment residents worried about retrofitting work being done on their building may have to do some research and speak to building code officials. Dreessen suggested they ask the following questions:

Is there an architect involved? Is there a building permit involved?

Are there proper inspections, and proper material being installed?

Who is the design team? Is it only an engineer?

What is the scope of the work being done, and does it comply with regulations?

However, the vast majority of projects being done in Canada are of very good quality, Dreessen said.

"And I would say in general, people shouldn't be that concerned."