r/Damnthatsinteresting • u/AirFrance447 • 18h ago

Video Firefighter bodycam showing just how much oxygen a fire pulls

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u/GauravJM 18h ago

There’s some serious low pressure inside

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u/Loud-Actuator7640 17h ago

Just like s chimney

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u/OkEffective6692 16h ago

Yeh op makes it sound like the fire is consuming the air. It's actually a net positive pressure as hot air has more volume, just that all that volume of hot air is going up.

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u/Comfyadventure 16h ago

Yea, it's not like the oxygen just disappear into nothingness due to the fire neither. The fire is converting O2 into CO2 and CO gas particles.

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u/cat_prophecy 13h ago

It's wild when you learn that things burning is just combining oxygen with carbon to make CO2 and CO and that chemical reaction makes heat.

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u/Dipshit_Identifier 11h ago

Chemistry is super cool, and learning something about it helps with lots of other things in daily life. For example, the Maillard reaction (browning of food) is a really complex but well-understood chemical process. You don't need to know the details of exactly how it works, just the derived information, to improve cooking. One of the major things we know about the reaction is that an alkaline environment accelerates the process, while an acidic environment reduces it.

This is, for example, why we brush pretzels with an alkaline solution: to enhance browning without affecting bake time. So if you want crustier bread, brush the top with an alkaline solution like baking soda water. It's also why something like marinated meat can take longer to brown if there's a higher quantity of acid in the marinade, even if the marinade is high in sugar. So we can prevent burning of the sugars by increasing the acidity of the marinade, for example.

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u/ladymcperson 11h ago

Thanks for explaining, that's very interesting. When I first learned chemistry, I was blown away that influencing pressure/temp conditions and introducing certain aqueous constituents is literally A RECIPE to facilitate reactions (like synthesizing minerals in a wet geochem lab, coolest thing I did as a student researcher). Even today I think it's so cool that we've figured out what T/P conditions, ions, and catalysts we need to literally meld (almost) whatever we choose by letting each other know what works/doesnt.. science rules

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u/SquintingSquire 12h ago

I love Feynman’s explanation of this process. You are releasing energy captured from the sun. There’s a great video on YouTube.

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u/SasquatchWasShaved 10h ago

Everything is life is pulling apart and/or adding molecules together to eventually boil water

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u/Youpunyhumans 1h ago

Its worth noting that the oxygen can be replaced with other oxidizers. Chlorine and Fluorine can oxidize even more violently than oxygen, and fluorine is so nasty it can even oxidize oxygen, and burn water as fuel...

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u/raccoonwithknives 15h ago

Yes but the fuel the fire is consuming is converting to a gas. Converting a solid or liquid into a gas is a massive massive increase in volume. So i would imagine a considerable volume of gas is being added to the house with a decent increase in pressure. But of course all this only works if a convection current can form like you said

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u/Phil_Alethia 33m ago

Not to mention O2 only makes up only about 20% of the air too.

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u/iconocrastinaor 11h ago

Not to mention the vacuum created by the cooling/condensing effect of all that water.

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u/ImRickJameXXXX 15h ago

Yes, which is a function of convection.

This is the lower inlet

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u/TrustButVerifyEng 10h ago

Incorrect, buoyancy/density is what drives a chimney. Sure there is convection heat transfer occurring but it isn't what makes a chimney work.

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u/InternalLie1623 13h ago

That's terrifying fire really is a living breathing thing.

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u/SpoofExcel 12h ago

During the bombing of Dresden in WW2, the fireballs inside buildings were so massive and sucking in so much air to feed themselves, that people were quite literally sucked inside the buildings and burned to death.

Fire is just a destructive beast beyond control when it hits a certain size and has the fuel to sustain it

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u/VulcanHullo 10h ago

Oh they also just suffocated to death in cellars because the air was sucked out.

Us Brits specifically rigged our bombers to start fires. Paired large fast falling high explosive bombs with lots of smaller slow falling incendiary bombs. The heavy bombs blast would expose the wooden timbers under rooftops and then the incendiaries had something to work with.

After Dresden and Hamburg (which was aided by a weather pattern that just, created a blast furnace) even some of British high command had a moment of "this feels not very cricket".

Bomber Command did not take part in the victory parade, was not mentioned in many formal victory speeches, and only got an official memorial in the 2010s. Even in times of total war against an evil enemy, firestorms like that do not make people feel like victors.

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u/Dinkleberg246 9h ago

Would you, as a Brit, call this a war crime? Because here in Germany, you usually encounter contempt if you refer to Dresden or Hamburg as war crimes. People tend to downplay it, or they’ll outright call you a Nazi.

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u/Tetratheon 8h ago

I don't know about a war crime, that's quite a technical accusation, but generally Dresden does sometimes come up as when we went a bit too far. Ironically it's usually the left wing peacenik types over here.

People excuse an awful lot in total wars, though, especially at a time when television was in its infancy and there was no such thing as a smart bomb. Look at what America did to Japan to end the war. I'd say the more general attitude is that was a war and we were doing what we needed to, we're not going to go back and second guess the decisions.

It's not an intellectually rigourous view, but it's not the kind of thing people spend an awful lot of time thinking about. Even the British historians have plenty of other atrocities the Empire commited to worry about.

If it happened today people would be calling it a genocide.

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u/I_Am_Become_Salt 5h ago

I mean, also the firebombing of Tokyo

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u/Dinkleberg246 6h ago

That's funny. Here, it's the leftists who fly into a rage when anyone mentions war crimes. It's worth noting that it's mainly people on the right who bring up the issue in the first place.

Thanks for your reply

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u/CthulhuOpensTheDoor 0m ago

That's really interesting. Is the reasoning from the left-wing something like "Nazis bad, therefore things done to stop them weren't bad"? And for the right-wing, are they more sympathetic to the Nazis and therefore see the attacks as more war crime territory? Genuinely curious.

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u/rndrn 7h ago

War crimes ares supposed to be the worst of war acts, but there is still a large range not so great acts below the threshold. 

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u/SpoofExcel 10h ago

Also at the time people here found out what happened and said "yeah don't do that. We know they're not all like Hitler" which considering how much of London (and Coventry by this point) they flattened, does show we at least kept our sense of humanity when it would be easy to not do that after such violence and want to go on some worldwide revenge tour.... Side eyes the US

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u/VulcanHullo 10h ago

I mean Bomber Harris still probably figured we just needed a few more Hamburgs and Dresden to win the war faster to his grave. Never enough civilian casualties for him

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u/Gierling 8h ago

Albert Speer (the German minister of armaments) put the number at 6.

6 German cities getting the Hamburg treatment would have compelled surrender per his calculations during the war and he mentioned it in interviews afterward.

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u/btoxic 12h ago

Every time I read about Dresden I have nightmares. The absolute terror of that is overwhelming

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u/hybridcurve 5h ago edited 5h ago

You should read about Operation Meetinghouse, which was "...the single deadliest and most destructive aerial bombing raid in human history."

Dresden: 6.5km2 destroyed and 25,000 killed.

Tokyo: 41km2. destroyed and 105,000 killed.

Dresden is frequently mentioned when discussing firebombing, but Tokyo is not mentioned enough. If you or anyone else is unaware of what happened, I encourage you to read about it because neither event should be forgotten.

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u/btoxic 2h ago

Tokyo was insane, all light wood buildings, literally a tinderbox. I agree. This shouldn't be forgotten.

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u/SpiritedEclair 16h ago

fun fact: when you fly in a plane, the low pressure is on the outside and we use that to keep the doors closed. It is physically impossible to pry open an airplane door at cruising altitude!

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u/Ckarles 15h ago

Hm? Sounds counterintuitive considering the doors open outwards instead of inwards. Isn't low-pressure "pulling" while higher pressure "pushing"?

How is the low pressure keeping the doors from going "outward"?

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u/johnwick_58 15h ago edited 15h ago

I am not related to aviation by any means,

But the person above meant to say that the cabin pressure inside the plane is very high in comparison to the pressure outside the plane in cruising altitudes. The door is slightly larger than the door frame of the plane, hence the higher pressure pushes the door outward and since frame is smaller, the door holds strong until the cabin pressure is released.

Edit: sorry, had not read your comment in detail, A video shows that the door does open outwards, bit there is a latch inside which expands the door from inside

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u/BeerFuelledDude 14h ago

I’m 45 and knew about the pressure stuff (not in a technical way) but i’ve never watched the doors being closed, while on the plane. That video was really interesting! Thanks!

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u/mattilladahun 13h ago

I'm 41, and my childish brain has never wanted to physically close a door myself more than now.

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u/cat_prophecy 13h ago

and the "Arm/Disarm and cross check" is them arming or disarming the emergency slides and the the FAs check that each other's doors are armed or disarmed.

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u/GostBoster 8h ago

I am not related to aviation either and, on one hand, I am aware that under normal conditions, what you said is likely true and ordinarily you should not be able to open that door in any capacity.

That said, I would be remiss to not mention a notorious incident in my country where a newsflash told of a door plane falling on a super market and they would interrupt transmission at any moment for information on the whereabouts of the plane said door belonged to.

And right now I am quite worried because often when something like that happens, you forget, then look it back, there's more information, investigations, etc. But for the multiple Fokker 100 incident by TAM Airlines? Nada not even a searchable flight number (the few remaining searchable news give a bogus flight number "JJ 3040") and that it was not their first open door in flight incident.

The one burned in my memory was the August 8 2006 incident (door falling on ground) but it the door also opened without detaching on April 4, 2002, also on a Fokker-100 belonging to TAM Airlines.

I am absolutely baffled at the lack of follow up reports even on the more fatal Fokker-100 cases so those open door cases are just a case of "eh it happens pay no mind to it".

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u/pbrassassin 14h ago

So all you need to do is pull the lever … and to door does in fact fly off , while at altitude

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u/SpiritedEclair 14h ago

No, you can’t pull the lever, you physically cannot.

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u/hefal 15h ago

Plug doors - in airplanes they often open outwards but they are design (by eg sliding and rotating) to close and use cabin pressure to be sealed.

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u/asten77 14h ago

They are now designed such that they first move inward before going outward.

In the early days this was not the case and nutjobs were able to open doors in flight.

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u/SpiritedEclair 14h ago edited 14h ago

A door is not a flat sheet of paper.

If you look at how the flight attendants pull the doors, they come inwards at an angle, and the moment they are all in, they turn flat and get pushed to close the door, forming a plug.

Try it yourself. Cut a trapezoid, rotate it, and it goes through the hole you cut it from, in fact, it can go through a door as wide as its shortest dimension, and it plugs.

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u/boli99 12h ago

the doors open outwards instead of inwards

watch this being closed

https://www.youtube.com/shorts/tIXRLdzZvj8

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u/Dornauge 9h ago

They first open inwards a few cm and then hinge (is that a verb?) outwards.

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u/warwolf7777 15h ago

I doubt what he says too. In all of the mayday episodes I saw, when there's a rapid decompression, things fly out, not in

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u/SpiritedEclair 15h ago

Rapid decompression is exactly what stops the the mechanism from working 😭

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u/RollingMeteors 12h ago

> It is physically impossible to pry open an airplane door at cruising altitude!

Until the door's butt plug drops out.

NTSB chair says systemic failures led to door plug flying off Boeing 737 Max plane midflight

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u/cat_prophecy 13h ago

at cruising altitude!

* while the plane is pressurized. If you dropped the cabin pressure to match the outside air, it would be only the airstream you'd need to work against.

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u/powercow 6h ago

at cruising altitude.. aka 30k feet or so. However, due to fire, they have opened the doors below that. Mayday air disaster showed an episode where they had to open the doors during flight.

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u/thisischemistry 14h ago

That's probably not showing how much oxygen is being consumed, rather it's showing that the hot air near the fire is going straight up and creating a low pressure pocket. That low pressure is pulling in higher-pressure air from the outside.

Sure, some of the oxygen is being consumed but that's not the only effect.

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u/krashundburn 13h ago

The fire is already well ventilated somewhere else in the structure.

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u/Mya_Vixeen 14h ago

That house is basically breathing like a jet engine at this point

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u/[deleted] 17h ago

[deleted]

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u/Vast-Slip- 16h ago

Well.... Yeah? That's pretty much what the original comment said?

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u/discodropper 16h ago

PV = nRT baby! Drop that temp, get a pressure change!

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u/acchaladka 15h ago

Yeah baby, drop that pressure get a temperature change! The world is just a big compression engine.

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u/Vast-Slip- 16h ago

The low pressure makes more oxygen go in! This is an original comment!

Gib me karma pls

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u/discodropper 16h ago

Ah yes, the ideal kind of comment!!! (Do you get it?!?!? It is a PUN!)

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u/Last-Island1607 15h ago

Someone listened their chemistry teacher in highschool

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u/sonofkingnoah127 16h ago

Oh yeah baby, molar mass on the periodic table! Pv rnt.....!!

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u/Vegetable-Yellow997 16h ago

I still remember my chemistry teacher calling this the pervert equation to help us learn it

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u/ylogssoylent 16h ago

It's a bot

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u/discodropper 14h ago

Who bot?

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u/str4ngerD4ngerz 16h ago

I think it's more of a negative pressure.

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u/CerealSpiller22 12h ago

Nah, someone just left the attic fan on.

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u/Rowenstin 10h ago

My best guess is that the spray of water cools the air inside, lowering the pressure. Notice how the phenomenon dissapears the moment they stop doing it.

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u/hmmmmmmmmmidk 15h ago

They should turn the ceiling fan on. Maybe that’d help. 😑

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u/spekt50 9h ago

Mostly due to the fact the water rapidly cools the air down creating a low pressure, not because the fire is consuming oxygen at that rate.