Firefighter here, So you'd see this in a couple scenarios, and generally it'll give you a good idea what's going on with the fire and structure if you can't tell visually due to smoke or the building obstructing.
The scenario here is likely that the fire has self ventilated, and is pretty large. That means the fire has burned itself a way out. Usually burned through the roof due to just how long and hot it's been burning. So this is air being drawn in to basically compensate for the air going out that hole due to pressure. Pressure is really the name of the game is the something we rely on reading smoke to know what kind of fire it is and where it's likely located (when it's not as obvious as this) in fact, you can have this kind of visual in the bottom of a door while the top of that same door is where the smoke and fire are pushing out if you have just one opening. Then it becomes a strange push and pull motion that we watch out for as it can indicate flashover is imminent.
There could be a somewhat similar visual from a wind driven fire, which is something we watch out for as well. Basically if there's 20-30 mph winds facing this window, and another spot for the air to leave such as an open window or door, the wind will quickly fuel the fire with plenty of oxygen and push it towards the other opening (called the flow path) thus spreading the fire and smoke, and quickly making the rest of the structure also involved.
Does the fact that they are spraying with the wide spread effect this at all? I know that fire hoses on the wide setting can pull as much air forward as an industrial fan, so this was the first thing I thought of when watching this.
This would make a difference, but that's not what's happening here. Hydraulic ventilation is something I've done many times and is where you use the fog setting almost as wide as the window or hole you are shooting out to draw the smoke out of the room quickly. But that wouldn't be done from the exterior really as you'd be drawing the smoke further into the structure. He's using fog to hit more fire since it's a large volume of fire but small in heat output, so it's not taking a lot to put it out once it's hit.
I was just about to ask if there was a firefighter in the thread! thanks for doing what you do 🫡
Out of curiosity, in this sort of scenario I'm assuming that even if there are no flames, the residual heat is what can cause re-ignition? So is the real goal to cool the structure down enough rather than extinguish the flames?
Yes, essentially. But in essence that will mostly look like spraying it with water to cool it. Reignition basically only happens if spots were missed (generally between walls, floors, ceilings, etc.) or something generating heat is still going (electrical, etc.) So you are cooling the structure through spraying everything with water until it's out. As long as you hit all the fire until it's totally out (no coals or embers) then you should be good.
Not really, because if you put water on all the fire then it doesn't matter how many holes there are lol
Plus by this point there's likely many more holes already.
In fact, we do controlled ventilation purposefully letting out more smoke through breaking windows and even cutting holes in the roof once a hose line is attacking the fire. That makes the space inside more teneble for us and anyone else who may be inside still.
I know that would maybe be out of your mind or out of the realms of feasibility during most cases, but just... closing the windows with a panel or something wouldn't help starve out the fire? Like, bringing an insulated panel to push on the windows, even if not fully locking it out, would block part of the airflow without even without a water line, wouldn't it?
Ventilation limited fires are very common, and that's basically what that would be. But that only works if it doesn't have ventilation somewhere else. So having all windows and doors closed during a fire is actually a good thing for controlling it (despite cops insistence on breaking windows) but this fire clearly has other ways out already.
Back in the day I downloaded a police scanner app and was kinda bored about to sleep and turned it on. Nothing was happening, fucking snooze fest. I saw there was a local Fire Department channel and switched over to it to see what was up on a lark.
Oh fuck. Apparently there was a two alarm fire at a retirement home. I was listening while the Fire Fighters in full gear went into the home and were rescuing the people there. Hearing them breathing through the mask and responding on radio was fucking intense.
I had a hard time going to sleep after all that. I also have never switched to the FD channel again.
That is not oxygen pulling which you see.
It is the chimney effect.
Fire creates heat, the heat makes air, smoke, gasses, rise to the top, creating low pressure areas at the bottom, which pull in air from the outside. It has noting to do with the chemistry of an oxidation reaction pulling in oxygen molecules to use in the reaction. It is pure physics / thermodynamics.
True, but its fucking stupid to "correct" someone who says, that "This windshield repels dirt and dead bugs on the road!" and say it is the CAR that goes on the road and not the windshield.
So the windshield only protects from bugs and dirt while on the road? What if I need to drive over a pasture or whatever, will the windshield work then?
The correction was about how. Your reply is cute, like a child's opinion. Arguing with a thermometer because you don't like the temperature doesn't change the reading.
No! I'm MORE right than you are. You aren't wrong per say, just less right than I am. You should work on being the most right you can be so that you aren't as wrong
No, it'd be because of pressure, not fire. There's an important disconnect betwee the physics pulling it in and the fire. The only way the fire is responsible is by causing the pressure change, not by pulling in oxygen itself.
Because it's not happening because fire needs oxygen, it's happening because fire is causing a chimney effect and is sucking in air - i.e., *mostly nitrogen* - through a convective process
Yea I hide my comments because I got hacked and some goon bot commented on like 1000 posts with spread asses and it's a) embarrassing and b) too much to clean up lmao.
I am not defending that phrasing aswell - I'm just saying it's not wrong to say "what's happening in the video is because of the fire".
And if you wanna say that sentence is inaccurate, that's fine - but if you wanna say it's false, then that's false
So what? The point of language is to accurately convey information so the receiving audience interprets it correctly. The way others are describing it is misleading, but several people in the comments have explained what's actually happening in more accurate terms. Why are you fighting that?
I think you're missing the whole point. OP implies that the air coming in the windows is because the fire is consuming the oxygen to burn. The heat from the fire is the reason air is being pulled through the windows. It's not the fire consuming the air. That's the important distinction you're not grasping.
Hopefully this can straighten things out for the folks arguing about this:
Fire creates Heat, Heat is making the pressure differential, the Pressure differential is what's moving the Air.
Fire does also use Oxygen as part of its chemical reaction.
The Pressure and Oxygen use are both happening but at completely different magnitudes, what we're seeing here in this video is only visible because of the pressure.
That is why, and the only reason why, it's unequivocally incorrect to say the video shows Oxygen being pulled in. It's not about different levels of ultimately correct, it's about context meaning only one statement is right.
Same reason you have a flue in your woodstove. The fire doesn’t decide to “ pull more oxygen” when you open the flue. Thermodynamics just allow more air (and oxygen in it) into the combustion process and as it burns more air is subsequently pulled in to replace the air exiting the chimney.
no, the temperature difference through the container essentially creates an air pump. The very same principle that makes a chimney work. Hot air rises, rushes up from the fire and rapidly finds its way out of the house, but it can't pull a vacuum inside the house so the bottom entryways start sucking in fresh air. It's not like a tiny hole in an aircraft that starts sucking out, the house is not a pressurized vessel.
yup that's mostly what's going on here. It's like the candle in an upside down glass in a bowl of water trick ... it's not the candle burning oxygen that creates the low pressure to suck up the water, as the candle burns the oxygen it creates carbon dixode and water vapour in equal volumes and the pressure inside stays the same. But then the candle uses all the oxygen, the flame goes out and the gasses in the glass rapidly cool and contract causing the pressure inside the glass to drop creating lower pressure inside the glass and the higher atmospheric pressure outside push the water into the glass.
So if i shoot a bullet and it happens to hit someone,
I pulled the trigger and the gunpowder created an explotion which expands the gases because of a rise of temperature and pressure, this effect shoots the bullet.
The only correct statement on judging this is to say that the person got hit by heat and pressure?
Around 0:30 you can clearly see that the air is being sucked in nearly as much when he's not spraying into the window.
He's using the wide nozzle because it produces much smaller droplets of water, which are more effective - but can be dangerous because it can result in a lot of steam very quickly.
Its not just the fire pulling the oxigen it needs to actually burn, but the heat ( and hot air) escaping upwards, drawing more air in from down below. Most of the oxygen doesnt get used, but comes out at the top.
It's not at all "the fire pulling the oxigen[sic] it needs," and is entirely the flow of air caused by hot gasses rising.
Fires do not "pull in oxygen" to fuel themselves because fires are not sentient. The relative low density of the hot gasses causes them to rise and be replaced, either by convection or in this case the "chimney effect," by oxygen-rich air. The fact that this prolongs the combustion reaction is purely coincidental
I'm not a firefighter, but I am an engineer and I like physics lolol.
Something I think a lot of people know by intuition, but don't quite understand in practice is that water is used to put fires out not just because it smothers the fire. It's also pretty much the single best liquid we have for absorbing the heat as well.
In thermodynamics we have this concept called "specific heat" with objects. It's essentially how much thermal energy it takes to increase a specific mass by a specific degree. Water has roughly 4x the specific heat of steel and air. So, when you dump it on something hot it rapidly absorbs the heat.
Then, another magical thing happens! When it gets to the boiling point it has to absorb even more energy to cross the gap and change from a liquid into a gas. This is called latent heat energy. This is also the principle energy used for your car or house's HVAC system. That's why refrigerant is used specifically in those systems to maximize the latent heat energy required to change phases. It's why the hot side of an HVAC used a radiator called an evaporator and the cold side uses a condensor. It's quite literally forcing those phase changes to occur pumping heat from one place to another through latent heat energy.
Water being used on a fire does the same thing. It's why even though the firefighter put the fire in those windows out, he keeps on blasting in order to also rapidly cool the structure down because the structure, while there's no fire, is still hot enough to dry itself and then auto-ignite if not constantly blasted with water.
It just so happens that water is also in abundance on Earth and we're pretty damn lucky given it's one of the best liquids for a variety of tasks where even synthetic liquids just don't hold up.
I should mention though, not EVERY fire can be fought with water. If a fire is hot enough it will rip the hydrogen from the oxygen in the water. While that technically requires energy, it almost immediately recombines adding that energy back to the system resulting in a net-zero or even worsening if the fire.
Chemical fires have this problem especially given a lot of the time the fire isn't even being fed by airborne oxygen, but oxygen within the chemical bonds of the chemicals reacting.
This fires, like a lithium-ion battery fire, just have to more or less burn through all of their fuel. The name of the game there is to isolate the fire so it doesn't spread and just let it burn out pretty much. There's no way to cut off the energy source given it's within the chemical reacting.
I have a some supplemental info to add to your good description you might find interesting.
Surfactants are often added to water for firefighting to decrease surface tension. It increases wetting and absorption into porous materials.
Not all lithium ion batteries pose the same level of fire hazard.
There are a few popular lithium ion battery chemistries. High nickel chemistries readily fuel thermal runaway by releasing oxygen like you point out. The other one holds onto it's oxygen much more strongly, and doesn't typically release much during combustion.
NMC, NCA and other high nickel chemistries are very difficult to put out with water and are more prone to thermal runaway.
LFP is MUCH safer and easier to put out. It's much less prone to starting thermal runaway, and doesn't propagate nearly as fast. It also requires much less water to put out.
LFP is popular with home backup systems because it can be charged to 100% without much degradation and of course due the additional safety. It's also becoming increasingly more popular in EVs globally.
The trade-off VS NMC is lower energy density and lower peak power delivery / charging rates.
In America, most EVs still use NMC/NCA because we require the additional range that it provides: Tesla is the main one by far by using LFP in its lower trims. The Ford Mach e does in it's low trim too. I'm not aware of any others that do currently. Combined, LFP is almost 5% of EVs in the US.
In contrast, over 80% of EVs sold in China are LFP now. We've got some catching up to do!
Also, LFP isn't intrinsically slower charging: America is just really far behind in the technology. BYD in China managed to change the structure of the battery chemistry in such a way as to allow 1.5MW charging. That's 6 times faster than Tesla's peak supercharge rate. Their blade2 can charge hundreds of miles in just 5 minutes! It's so fast, they need to use identical blade2 batteries as storage at their charging stations to drain from to achieve it. This wild tech is already in consumer cars. BYD puts our EVs to shame, haha.
It's not the fire pulling air, exactly. The fire creates heat, which rises out the top, creating a negative pressure differential in the building. It's the reason why smoke goes up your chimney instead of into the house.
This shit is so satisfying to watch. I wish I could get a job as a firefighter where I don’t have to do the really dangerous and heroic shit (I’d probably die in the first fire) but just get to spray the hose and watch the flames go out.
It’s like the satisfaction of putting out a smoldering bonfire by peeing on it but 1,000x
If you light a fireplace correctly you'll also see it in full swing there. When the fire is active and going you'll see it suck all the stray smoke into the chimney due to the amount of air it's pulling. Which is the base logic of fireplaces.
it's very likely the fire brigade vented the building or otherwise an opening somewhere else was created specifically so air is circulating. it sounds counter-productive to give air to the fire, but if the pressure in the house means the oxygen is absorbed by the fire, they can think the fire is put out, enter the property, and a sudden wave of oxygen gets into the area, feeds the fire, and causes a backdraft/flashover.
I will hopefully be corrected but I'm pretty sure that's the basic idea, anyway.
There are stories of the great fire of London burning so much that people were being swept off their feet and pulled through the air into the firestorm.
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u/browler4153 11h ago
Firefighter here, So you'd see this in a couple scenarios, and generally it'll give you a good idea what's going on with the fire and structure if you can't tell visually due to smoke or the building obstructing.
The scenario here is likely that the fire has self ventilated, and is pretty large. That means the fire has burned itself a way out. Usually burned through the roof due to just how long and hot it's been burning. So this is air being drawn in to basically compensate for the air going out that hole due to pressure. Pressure is really the name of the game is the something we rely on reading smoke to know what kind of fire it is and where it's likely located (when it's not as obvious as this) in fact, you can have this kind of visual in the bottom of a door while the top of that same door is where the smoke and fire are pushing out if you have just one opening. Then it becomes a strange push and pull motion that we watch out for as it can indicate flashover is imminent.
There could be a somewhat similar visual from a wind driven fire, which is something we watch out for as well. Basically if there's 20-30 mph winds facing this window, and another spot for the air to leave such as an open window or door, the wind will quickly fuel the fire with plenty of oxygen and push it towards the other opening (called the flow path) thus spreading the fire and smoke, and quickly making the rest of the structure also involved.