I mean, cold itself (within Earthly limits) doesn't put out fires. In fact, it might make them burn better due to convection.
That said, this reminded me of a lake in Chelyabinsk that is so polluted you can set it on fire according to some locals (I don't remember the video, it was a few Russians filming a short tour of the city)
Sorry that was ambiguously worded. My point was that nothing like the CWA was even floated afterwards, since everyone knows the politics of today wouldn't allow it.
Fires are less likely to ignite in very cold weather as the environment is taking energy out of the reaction. Once it gets going cold doesn't matter much.
It appears humidity doesn't really impact an already burning wildfire, but lower humidity means drier fuel which makes the fire more likely to spread. Conversely, higher humidity can make a fire less likely to spread to moister fuel[1]
But any fire is magnitudes hotter than -50. That cold is a blip on the fire's radar. Once started, and as long as there's fuel and oxygen, it won't stop because of negative Celsius temperatures.
It can significantly slow down wild fires which need to heat a constant supply of fuel to ignition temperatures. Wood burns at 180 degrees Celsius, so the difference between 20c and -50c is +160C vs +230C or over 40% more heat.
This is especially impactful when looking at how easily sparks propagate fires across gaps.
A typical wildfire is not putting much of its overall energy output into bringing fuel up to combustion temperature, though. The combustion energy in a kilo of wood is measured in megajoules; the amount of energy needed to elevate the temperature of a kilo of wood by a degree is measured in kilojoules. So while you're right that the energy budget needed to combust new fuel goes up by 40% or so if the fuel is at -50°C, the energy budget going into that is only a percent or so fo the total energy the wildfire is putting out. The rest of the energy beyond what's needed to bring fuel up to combustion point is going into making massive walls of glowing flames, mile-high convection columns of air, sending smoke thousands of miles, etc., etc...
That is, in many ways, precisely what makes it a wildfire, rather than a smouldering ember.
In the limit - when a fire is dying out - then I guess, for sure, changing the fuel temperature can sap a larger part of the energy budget.
The point is propagation speed. A burning tree surrounded by acres of burning trees is largely irrelevant at that point. It might happen to produce spark that travels miles, but that’s relatively rare. Which is why firebreaks can be useful.
My uncle used to joke that his car ran better in the mountains because the air was cleaner and thus had more oxygen. He was not serious, but in case of cold air there would be more oxygen per unit volume due to density so that might improve the combustion.
Ignoring, of course, the fact that "in the mountains" means an increase in altitude and thus a decrease in air density. My carbureted vehicles that were jetted for sea level always ran like shit in the mountains. And fuel injected vehicles run fine (because they can adjust for the altitude on the fly), but with noticeably less power.
Apologies for pedantically deconstructing what your uncle meant as a smart-assed joke.
Lower air density means old carburetted engines run leaner - which since most such engines are tuned to run slightly rich for reliability in favour of slightly lean, gives you more power up until the point they overheat and if they're a 2 stroke motor relying on the oil mixture in for lubrication the fuel, seize.
One of the old traditional racetracks here in Australia is Mt Panorama at Bathurst. It's got about a 180m elevation change between the start/finish/pit straight and the top of the mountain. Back when they were allowed to race motorcycles there, old 2 stroke racebikes were notorious for seizing at the top of the hill if they'd been jetted down at the bottom and hadn't been set "rich enough" to allow for the altitude change. Many many riders crashed and said "It was running really strong, til it locked up on me and spat me down the road..."
(No apologies at all for my off topic response to pedantry...)
Mmm, pretty sure sea level carbs run rich at altitude. Less air means a need for less fuel for the same ratio. But the fuel side didn’t change because we didn’t rejet, so now too much gets pumped in. If I’m guessing the bikes might have seized at the bottom of the hill instead? Or it just took until the top before the damage was done.
Ahhh, yeah - you're right. I've got it back to front there.
In my defence it's been a long time singe they've been allowed to race motorcycles there. At least 20 years. And now you mention it I do recall bikes seizing at the end of pit straight, right down the bottom of the hill.
Could the lower air pressure at altitude still end up pushing less fuel in through the jets? It's not obvious to me how this would behave when deviating from normal conditions.
Some Rotax two-stroke engines running pre-mix have been used in ultralight aircraft, so I think appropriately sized altitude-compensating carburetors designed to run a petrol-lubricant mixture may be commercially available. However, I imagine it's pretty expensive to put aircraft parts (even ultralight parts) on a racing motorcycle.
These carbs use an aneroid to move a needle valve at the base of the jet as the atmospheric pressure changes, effectively dynamically re-jetting the carb on the fly.
> And fuel injected vehicles run fine (because they can adjust for the altitude on the fly)
A bit of pedantry: modern automotive electronic fuel injection with exhaust oxygen sensors adjust much better to altitude, but the first aircraft and automotive fuel injection systems used the Venturi effect acting on a spring-loaded diaphragm to estimate mass flow rate, and simple mechanical computer to adjust fuel flow needle valves. Early aircraft mechanical fuel injection systems contained an altitude-compensating aneroid, but I doubt early automotive models did.
Many small recreational aircraft still use altitude-compensating carburetors that contain aneroids that act on needle valves to compensate for altitude.
Even today, the oxygen sensor is a relatively expensive part, and it's possible that early electronic automotive fuel injectors didn't measure and compensate for oxygen concentration in the exhaust.
So, an old automobile retrofitted with an aircraft altitude-compensating carburetor may very well compensate for altitude better than an early fuel injected automobile. Though, I assume only a handful of cars have ever been retrofitted with altitude-compensating carburetors.
Heat engines generate power from a difference in temperature. The larger the temperature difference, the more power. You can increase the temperature difference by making the heat source hotter or by making the heat sink colder.
The air pressure is also higher at colder temperatures so if the fire is underground it'd have more forces working in its favor to cycle fresh air to it and the relative temperature difference between the freshly heated and exhausted air and the fresh air would be wider causing there to be more turbulence cycling the air around.
The turbocharger is what helps at high altitudes, not the intercooler which just cools the air. The turbo packs more air in to the engine, which helps at sea level but makes a big difference at high altitude. Superchargers do the same.
It's actually one way of putting out otherwise very persistent fires, especially the ones that like to only smoulder (really nasty chemicals, metal compounds, etc.) Removing heat from the reaction lowers the ignition temperate of the surrounding material to a point that fire dies out on its own.
Side note: it doesn't work that well on burning plutonium.
I think heat is meant to represent the ignition source. The reaction creates heat which then disapates into cold, right?
If this were to happen in absolute 0, would it be possible to sustain a fire? From learning more (just now) about absolute 0 seems it wouldn't but for other reason.
Can someone answer this, I find it a really fascinating question. How does cold effect fire if at all?
Cold affects the speed at which molecules are moving around. Fire is a phenomenon produced generally by exothermic chemical reactions between molecules. The part of the fire you see is, if I understand correctly, the photons emitted by excited electrons moving to a lower energy state after the reaction.
All other things being equal, the colder it is, the less the candidate molecules are moving, and thus the less likely they are to encounter each other and react. IIUC almost all chemical reactions are less vigorous at lower temperatures, disallowing convection of course.
It would go out. In a room cold enough for Oxygen to turn solid, there would be no gaseous oxygen to sustain the match’s combustion as it falls. The wood would have some latent heat, but not enough to re-ignite itself in a room that cold.
Pure oxygen won't burn anyways. What would it oxidize? If you had frozen a mix of oxygen and hydrogen (without the two separating) it would be possible to ignite and burn it.
Truly pure oxygen won't burn, it needs fuel. So, what would probably happen is it would burn super bright for a split second as the match itself was consumed, and then extinguish itself as it has no more fuel.
> I mean, cold itself (within Earthly limits) doesn't put out fires
This is not a meaningful phrase when cold is the absence of heat. You need to describe the motion of the cold air against the warmer system to get a meaningful phrase.
Being able to set a river on fire is not terribly unusual for a polluted river. I remember about ten years ago I posted up at the schuylkill, waited for an oily patch, and was able to set it on fire for about 5 seconds. These oily patches are uncommon. I have no clue where the oil came from but with the schuylkill it's anyone's guess. The patch itself is necessary for lighting the river on fire; you can't just set fire to an arbitrary section of river.
Things that are deemed to be fuels emit way more energy than energy needed to heat air from ANY temperature. The fire would continue even if the air was liquid.
Smouldering happens on the surface of the material and not in the gas like in the flaming combustion. Compared to flaming combustion smouldering combustion is slower, lower temperature (900 C) vs and flameless. Smouldering is typical for porous fuels like peat.
The burning is sustained by heat. The burning beat is little underground. The burning peat is insulated so that the heat does not escape and the smouldering can continue.
Peat fire is much like gunpowder fire, just much slower. Peat naturally accumulate nitrates (saltpeters among others) which are essential in the gunpowder burning process.
I recall making plenty of fires while camping well below freezing, even below -10F. There really wasn't a significant difference in the behavior of the fire at any temperature. Unless you count difficulty in starting it due to numb fingers.
>Pillars of smoke filmed over the areas hit by last summer’s wildfires despite the current long spell of extremely cold weather.
Wouldn't cold weather amplify the effects of large fires? After all, cold air is more dense, thus provides more of the oxygen necessary to burn hotter. It also has less moisture.
Not an expert. Just a random guy thinking out loud.
To burn you have to dry out the fuel matter and warm it up to its combustion T.
If the air is -50, the fire has to give up enough enthalpy to not just dry up and warm up the wood, but also melt the water in the fuel. That energy cost is huge.
That cold air is dense won’t come close to overcoming the enthalpy of melting and having to dry the fuel.
Also that the air is “dry” is irrelevant at -50C. The air is dry because it can’t hold onto moisture so it won’t dry out the fuel. Also, the water in the fuel is frozen so even if the air was relatively dry there would still be a huge kinetic barrier to sublimation.
I’m not an expert either but I have experience with getting fires to burn. Starting a fire in the cold is quite a bit harder. Mostly because if it’s cold, then it’s the middle of winter, and that means the kindling is covered with ice and snow, which has to be melted and evaporated off. A dry log has a lot of potential energy in it. A frozen log full of water and snow has zero or even negative potential energy, as in, even if you get it to burn it might take more heat out of the fire because of the ice than it adds back by burning.
But, that might not apply to peat fires because 1) larger, hotter fires make more efficient use of fuel, especially if they are in some insulated space where all the heat is not going straight into the atmosphere and 2) the peat might be dry.
Scouts learn to start a fire in any weather - even cold rain. You split the log and use the dry wood inside for kindling. Wood takes a season to dry in the first place, and isn't going to get wet (inside) just because it's raining. FWIW
And peat is nowhere near as dense or insulating as wood. Wood doesn’t really want to change temperatures easily, which is partially why we make floors out of it.
Any fire with flames is something around 600C and up to even double that. Air is relatively cheap to heat up. I'd wager the combustion process, once fully started, won't suffer much if the ambient temperature is -30C or +30C: the fire is still on a temperature scale that's an order of magnitude higher.
Even on a summer day a good breeze of wind or just blowing into the fire too hard yourself will put it out but only if it was just starting. Once the fire is rooted in something more solid, combustible material it will easily heat up any fresh air that is conveyed into the fire.
Though if this is a peat fire the water in the peat may have partially evacuated during the freezing process - I'm not so certain that the volume needing to be sent from ice -> water -> vapor would take more energy than the larger volume sent from water -> vapor... I really have no knowledge of ratios here but there are at least some processes working against increasing the amount of energy that needs to be expended to heat the surrounds.
Additionally, if this fire is mostly underground then it's likely that you've got some oven action going on where a lot of the heat produced by the fire isn't just whisked away by air to dissipate to nothingness - instead it's trapped by the insulation of earth and being converted into phase changes more efficiently.
We see record low temps for weeks in Dec/Jan combined with the worst fires for 40 years. I don’t think the article is saying “it’s hard to have fire in colder terrestrial temperatures,” it’s saying “despite ‘cooling off’ we are still burning.”
A couple thoughts come to mind, the first of which is that this seems like an unfortunate head start on the next burn season. To the extent these are still burning as things warm up and thaw, I assume they start to significantly spread and grow.
in the ground the temperature doesn't swing that much, and Yakutia is permafrost zone. It is just a juxtaposition of the forest in the snow which usually means no fire and the fire under that forest that looks strange at the first look.
The submitted title was "Zombie fires in northeastern Yakutia continue to burn at air temperature of -50C". We changed it to what the article says.
Submitters: please don't rewrite titles like that—this is in the guidelines: https://news.ycombinator.com/newsguidelines.html. (But if the article title itself changed, obviously that's different.)
I have a feeling the Siberian Times updated the headline. Normally I spot when the HN title differs from the headline of a news article, and i think I’d be especially observant with this unfamiliar "zombie fire" phrase. But I didn't notice anything amiss when I opened this one up originally.
I think the Centralia fire is a great reference - or really any coal seam fire. The interesting thing to me is how this fire is continuing among blisteringly cold surface temperatures - but then again those fires have very little exposure to the surface and earth insulates extremely effectively. It only takes a few feet of earth to effectively dampen surface temperature changes - which is why ice houses were such a commonly used tool.
Every single Putin's friend has become a dollar billionaire and they build multiple big palaces/resorts/etc. for him. But no money for fighting wildfires...
Regardless of any involvement of a government or any factors of corruption - I'm just purely interested in the fact that nature could sustain a fire like this in -50C weather.
I am confident enough in my general knowledge that I can be interested in an article on a thing that I can rationally explain but never imagined independently. It's interesting that this fire is happening in blisteringly cold temperatures which is against my intuition as a being that feels like 110F is pretty hot and 40F is pretty cold.
That said, this reminded me of a lake in Chelyabinsk that is so polluted you can set it on fire according to some locals (I don't remember the video, it was a few Russians filming a short tour of the city)