It’s easy to get romantic about fire. The burning embers, flickering flames, a wood stove crackling in the cold of winter. But when you add man-made materials, furnishings, plastic, foam – even the materials your home is built from — well, that’s not the time for romance. That’s time for the science.
So come gather round the bonfire and hear the tale of how things burn – promise there won’t be a singalong.
As you take in the wood burning in the fireplace, what you are watching is the simple process contained in the Fire Triangle – oxygen, fuel and heat. Chances are, whether you built the log house, schoolhouse, or cone, you have a fire in front of you that is the result of fuel (the wood), heat (matches, a long-tipped barbecue lighter, or the two sticks you used trying to show off for your kids that has now resulted in injuries that you won’t ever disclose. No, this is not experience talking, why do you ask?) The heat is not just required to ignite the fire either, but to maintain it, as it preheats the surrounding fuel and air to make it easier to burn.
Then finally, a key component: oxygen. In order for the process that results in the ignition of a flame, we need the chemical process known as combustion: a high-temperature exothermic (heat releasing) redox (oxygen adding) chemical reaction between a fuel and an oxidant.
Put together wood, heat and the oxygen in the air – or from your consistent attempts to blow on the fire – and you will have combustion. It is up to you whether you become Tom Hanks in “Cast Away” proudly chanting “I…have made fire!”
But the fire triangle is a bit, well, outdated. It assumes that every fire is simply the reaction of three simple elements, and that it is therefore predictable, and easy to control.
That’s why the modern understanding of fire now includes The Fire Tetrahedron.
Say you’re sitting by the heat, minding your own business while being hypnotized by the fire (it can happen! *cough read this cough*) and someone walks past and throws a piece of plastic on it. Immediately the smoke changes colour ever so slightly; the smell is noxious, and the fire burns oddly.
As a petroleum product, plastic burns very differently from wood – and in our modern life, you could argue that the amount of plastic in our homes dwarfs that of wood. That’s why there needed to be another element to our understanding of fire.
The Fire Tetrahedron, and a new view of fire dynamics, takes into account the chemical process that now influence the way fires burn, and the way we fight them.
Modern houses are not built, or furnished with the same materials they once were. For instance, any homes now include Oriented Strand Board (OSB) for economic, efficiency and structural reasons.
But this board, made of thin strands of aspen or poplar held together by an adhesive, causes a chemical reaction that makes fighting fires in modern homes something that requires a scientific understanding into off-gassing.
To demonstrate this reaction to new recruits, Greater Sudbury Fire Services (GSFS) Chief Training Officer Sean McMahon and Deputy Chief Training Officer Dan Turnbull get a little help from the students at Lockerby Composite School’s Science and Technology Education Program.
The students get to spend a day exploring the firefighters’ training facilities in Azilda, get a great lunch and a wonderful experience; in return, they build “dollhouses” of OSB, complete with rooms, doors and second floors, so that GSFS can…set them on fire.
In the beginning, a small fire set in one bottom compartment – and set well, using Turnbull’s skill, experience and special pine kindling he brought from home.
It’s a lovely burn at first, with the smoke conjuring images of camping. As the compartment continues to burn, small pockets of “campfire” smoke begin to exit out the compartment (or room) beside the one with the fire inside. Then it moves to the upper compartments.
“So there’s all that pressure building up inside the structure,’ says Turnbull. “There’s areas of high pressure and low pressure in the structure. So as the fire is burning, it’s creating an area of high pressure, which it wants to escape (from) into an area of lower pressure. And it’s escaping through the structure like that.”
Then, after some time, the smoke begins to change. It is yellow, brownish-yellow, like that of the harshest cigarette you could imagine. The heat from the fire is beginning to build, and that heat is causing the OSB to off-gas. There are now fumes building in the air – and they are not just toxic, but flammable.
This is quickly proven the moment McMahon lifts a lit torch to gas-filled smoke, and it instantly ignites.
But if there isn’t a trusty firefighter with a blow torch, those fumes are building, and building, and building, within your home. And what if it is off-gassing not just from the OSB, but from polystyrene, insulation, foam mattresses and couches, and polyester furniture and clothing – to name but a few.
This build up doesn’t just have the potential to destroy your home, it has the potential to cause further reactions – reactions creating heat so intense that it can penetrate firefighter’s safety gear in seconds.
This is the reason that so much of modern firefighting techniques centre on the ability to read the fire, and predict its next moves. Whether that means new ways to apply tools, or warning signs that shouldn’t be ignored.
Flow Path, for one. “A lot of our fires are wind driven,” said Turnbull. “Air has a huge effect on the fire and how it progresses through the fire.”
If you’ve heard a somewhat recent push for the closing of bedroom doors while sleeping, or the closing of doors behind you when you are executing your family’s fire evacuation plan, it’s because of this understanding of how air works within a home fire.
If you’re a fan of smouldering fires and smouldering actors, you may have seen the movie Backdraft. Though the movie is fiction, this often fatal fire response is quite real.
“A backdraft happens when a fire is burning, but it’s taken up all the oxygen that’s available in the room, and it therefore wants to go into its decay phase,” says Turnbull. “All that it requires is oxygen, so as soon as the door opens or something like that, it’s a simultaneous event where the entire room is in flames.” Instantly, the fire gets its missing piece of the Tetrahedron, and the room is once again engulfed in flames.
Another fearful sight is the rollover – not just for its own destructive potential, but for the even it precedes. A rollover describes when flames ‘rollover’ through the smoke. It precedes a flashover.
A flashover is an absolutely terrifying event. “When all the products in the room (furnishings, building materials etc.) are giving up sufficient flammable vapours that they can ignite simultaneously – a flashover event is a very volatile event – it’s something that firefighters can’t survive. Even our gear isn’t strong enough to protect us from that type of heat.”
Surprisingly, this can be made even worse by the trend toward open concept homes. More space around and overhead for gasses to build up, more chance of rollover, then flashover.
Thankfully, once again it is science to the rescue. Now that there are training facilities, research labs and firefighting organisations focusing on fighting fires efficiently and safely, there is an understanding of why certain techniques work, and why some don’t.
For instance, you may think that opening all the doors and windows on a home with building gas might be the best way. So did the firefighters. Until they learned that only added “more fuel to the fire,” a.k.a. oxygen.
They now know that adding ventilation to the roof of the building is the best way to allow gasses to escape, while they close all doors behind them. (Special note: you should too. Close your bedroom when you sleep, close the doors behind you if you ever have to escape your home.)
And in another nod to the tetrahedron, firefighters also employ foams both to suppress fuel sources, and to add a layer of “bubbles” to prevent oxygen from penetrating to the heat.
They have also learned that a co-ordinated approach is vastly superior to single-combat – to use the term loosely. So much so that they frequently first work on what’s called “fighting an exposure fire,” while waiting for the whole team to arrive, which in practice could look like them spraying the neighbour’s house instead of the house on fire. Why this seems like a very poor commentary on the year 2020, it is actually better for their purposes to wait for the team to arrive in full before attempting firefighting efforts. And that team can often be close to 15-20 people.
“It takes quite a bit of staff to do this job well,” said Turnbull. “There has to be that fire attack team, there has to be a ventilation team, there has to be the forcible entry team and the team actually pumping the water, as well as the supervisors and commanders. It does require quite a bit of people to do the job properly and safely.”
And because every word about fire should be followed by a few safety tips (always keep your smoke detectors and carbon monoxide detectors working and up to date, have a fire evacuation plan for your family and practice it before it’s needed) you should also take heed of how firefighters are working with new materials and new homes – even that smoke inhalation is more toxic now due to new fumes.
So while you enjoy the campfire this summer, watching the smoke curl and the flames flicker, regale your guests not with tales of your fire-creating abilities (tried this already, it is less impressive than you think) and focus more on how much you know about fire-fighting abilities.
Now go enjoy your marshmallows.
Jenny Lamothe is a freelance writer, proof-reader and editor in Greater Sudbury. Contact her through her website, JennyLamothe.com.
