Fire-blocking chemicals promise safer buildings

I peer into a large vat with a perfectly transparent liquid – a special fire retardant for wood products.

“You can drink it. I can,” says Stephen McCann, general and technical manager of Halt, a timber processing company in Belfast. “I wouldn't recommend it,” he adds, however. Apparently it is very salty.

But in tests, this liquid, which contains a substance called Burnblock, was shown to prevent fire from spreading through wood.

In the video the company shared on the Internettwo small house models are burned with a blowtorch. One, treated with another product, is engulfed in flames to the point of collapsing. The Burnblock-treated model is heavily charred in one corner, but otherwise remains unharmed.

What is Burnblock? Nobody will tell. Neither Mr McCann nor Hroar ​​Bay-Smidt, chief executive of Danish firm Burnblock, would confirm the ingredients. However, documentation from the Danish Institute of Technology on Burnblock's website states that the flame retardant ingredient is a “natural component of the body” and that the mixture also contains citric acid and a “natural component of some berries.”

Fire retardants, chemicals added to foods to slow their burning process, have existed in various forms for centuries.

But many fire retardants were developed in the 20th century. very toxic. “There hasn't been a lot of investment in replacements, so now suddenly people are scrambling to find them,” says Alex Morgan, a chemist and fire-retardant materials expert at the University of Dayton Research Institute in the US.

“When you try to burn Burnblock-treated wood, the material forms a protective layer of charcoal,” explains Mr Bay-Smidt. “It also releases some water,” he adds. “This helps absorb heat and slows the spread of fire.” And this prevents oxygen from being supplied to the flame. You can add Burnblock to other building materials, including dried sea grass, he says.

Halt, which has been operating in Belfast for almost four years, supplies Burnblock treated timber products to hundreds of locations across the UK and Ireland. From restaurants to hotels and even HS2. For the latter, Halt provided treated panels used to fencing construction sites in tunnels.

“Getting out of the tunnel can be quite difficult, so they need as much time as possible to evacuate. [in the event of a fire]” says Mr. McCann. I ask if any buildings or structures constructed from Halt treated timber have ever been exposed to fire and the answer is “No.”

In one of the Hult buildings there is a huge machine called an autoclave, consisting mainly of two large horizontal pipes. The top one is the cleaning fluid reservoir I saw earlier. When the tube underneath is loaded with pieces of wood, it first subjects them to a vacuum to open the pores of the wood, Mr. McCann said.

Pressure appropriate to the type of wood is then applied along with the treatment fluid.

“This pressure forces the fire retardant to penetrate into the core of the wood,” says Mr McCann.

The wood then goes into a large kiln where it is dried, a process that can last from 10 days to six weeks. This is handled with care: drying too quickly or too slowly can cause the wood to warp.

“Wood is an amazing material,” says Richard Hull, emeritus professor and fire-retardant materials expert at Lancashire University. He refers to wood's ability to absorb cleaning fluids into its pores. “You can ultimately change its combustion chemistry,” he says.

However, Hull is often skeptical of new flame retardants. He notes that some ideas came and went. “There was a lot of work done on clay nanocomposites in the early 2000s,” he says. “Now, 20 to 25 years later, essentially 99% of that has faded away.”

“While wood tends to burn at a fixed rate, making plastic fire resistant is a different story because plastic tends to burn at an accelerated rate,” he explains.

Dr. Morgan adds that he calls polyethylene, a type of plastic commonly used in construction, “solid gasoline” because of its similar chemical structure and ability to burn quickly.

Australian company First Graphene says it has found a way to slow the spread of fire in plastic by adding graphene, tiny flakes of carbon atoms arranged in a honeycomb lattice. Michael Bell, managing director and chief executive officer, says the company's PureGRAPH solution has already been added to products such as safety boots and conveyor belts used in the mining industry.

First, graphene claims that it works by forming a protective gas barrier, preventing the release of volatile compounds before ignition, as well as a layer of charcoal in the event of ignition. But graphene is a notoriously mysterious material, and the company says there may be other mechanisms at play that are not yet fully understood.

Can graphene affect people's health after a fire? A spokeswoman said: “There is no evidence to suggest that graphene poses any health risks. The industry continues to test and evaluate these aspects.”

In the UK, Vector Homes is preparing to license PureGRAPH to producers of plastic pellets that could be used to make building materials such as façade panels.

Experiments show that graphene actually reduces the ability of plastic to burn. “It scored the highest in these tests,” says Liam Britnell, co-founder and CTO.

However, buildings are not only at risk from fires that start inside them. “The number of forest fires has increased” says Dr. Morgan. That's why Eric Appel of Stanford University and his colleagues are working on gel-like fire retardants that can be sprayed on a home hours before a wildfire reaches it to limit damage.

Professor Appel hopes to soon test this substance on mini-structures or mock-ups of houses.

Laboratory tests showed that when exposed to flame, one of the gels he was working on bubbled, forming a porous airgel structure inside that provided high fire protection.

“As soon as I saw him do it, I thought, 'Oh my God, this would be perfect for this,'” Professor Appel recalls.