cold fire

Factual Questions
21

people, look.

To say that ambient temperature will not affect a flame is, simply, just stupid. A flame is a self-sustaining combustion reaction. We all exist only because of such chemical reactions. If if gets too cold out, no matter how warm I may have been before, I will stop living at some point. All of the reactions within myself that generate heat will stop, mainly because they don’t generate enough heat.

We all know that there are places on earth cold enough to kill me. Philadelphia tonight may be just that (hoping to god not). Can it be cold enough on earth to snuff my last cigarette before passing onto the great eternal?

jb

22

Outer space isn’t really a good example. Temperature refers to the motion of molecules, so you can’t really define a temperature for a vacuum. There’s no ambient heat, but there’s also nothing to carry away heat.

It’s conceivable for the ambient temperature to be low enough that combustion could not occur, but I don’t know what that temperature would be for a cigarette.

23

Probably around the point where oxygen turns to a liquid, and like I said before, that is not a place where I want to be.

24

why is it just for oxygen to be a liquid? I understand that that would be a big breaking point for a flame, but aren’t there other considerations?

hypothetical: cigarette cherry needs to be above 150. if it’s normally 60 out, cigarette burns fine. that’s a temperature difference of 90 degrees.

let’s say ambient temp is 30 below. would the cigarette burn slower? well, if it were 110 degrees out (and the cigarette is also at that temp) wouldn’t the cig burn faster? I feel that it would (again, only feel- no real cites here- sorry).

I guess the question we’re looking for isn’t “can itbe too cold for a fire”, but “does ambient temp affect burning rate”? I won’t open my empty mouth until we can get a good answer to that.

peacables,

jb

25

Well, if you look at the chemistry of reactions…

For a reaction such as combustion to proceed, it needs starting materials and enough energy to get through the transition state. That is, there needs to be a certain amount of energy for the reaction to start. For a cigarette, that energy is provided by a lighter, or match, or hot engine, or something nice and hot.

Combustion is indeed an exothermic process. Normally, this reaction will proceed apace quite nicely, as long as the starting materials (oxygen and tobacco) remain extant. Cigars go out because the burnt material prevents oxygen from getting in. Cigarettes have additives that aid in keeping the reaction going.

However, just because a reaction is exothermic (ends at a lower energy state that it started at; gives off energy) doesn’t necessarilly mean that that reaction will spontaneously continue. For it to be spontaneous, the reaction given off needs to be equal to or greater than that needed to start the reaction.

Since the combustion is nicely contained in the cherry, that heat is, in almost all conditions, enough to keep the reacion going. However, it is very possible that there is a temperature here on Earth where the reaction cannot spontaneously proceed. I doubt, however, that anyone has ever found that temperature, if only because, on finding it, they tend to either die or get away from it before lighting a cigarette.

If you want corroboration on “heat is necessary for a combustion to continue”, find out how a fire extinguisher works. I believe the principal behind them is not that they use CO2, but that the rapid expansion of gas cools that gas considerably. They use CO2 because it’s cheap. I’ll look that up.

26

Okay, found info from
“Fire Extinguisher,” Microsoft® Encarta® Online Encyclopedia 2000
http://encarta.msn.com © 1997-2000 Microsoft Corporation. All rights reserved.

Four types of extinguishers. Two use the principal of cooling a fire until it can no longer proceed. The CO2 extinguisher is not one of these types, but is indeed used to flood the combustion site and drive away all oxygen.

27

I understand that Stuyguy argued against this point in the earlier thread, but doesn’t water put out fires:

not because it smothers them

and not because it removes burnable materials from the fire,

but,

because water takes up so much heat to move from a liquid to a gas?

jb

p.s.- okay, so I broke my promise. I have to pee badly as well. surely that makes up for a broken promise.

28

Bitte. On earth? Is there a trick to this OP? The tip of a cigarette burns at ~ 1100F to 1300F. We will use 1200F, which is 1660R. The coldest recorded temperature on earth is -129F or 331R. I have seen people smoke cigarettes at 0F, 460R, and below outside of buildings.

Thus, the heat transfer effect due to conduction and even forced convection, if the wind was blowing let’s say 5 to 10 mph, relative to 0F and -129F is h~(k/k)x(1660-331)/(1660-460) = 1.1075. The radiative heat transfer to the air and even to outer space on a clear night, can be assumed negligible to the transfer modes above. The boiling point of oxygen is 162.34R (-298F). It’s partial vapor pressure difference at 0F or -129F is relatively insignificant, there is more than sufficient oxygen for combustion at -129F.

Now is a ~11% potential increase in heat transfer from the tip of the cigarette to the ambient air enough to affect the its combustion … no. The cigarette would just use more of the available oxygen, being in excess, to continue its combustion. In fact, only near the liquid point of oxygen would the combustion be affected and this would not be due to ambient temperature effects.

Now if you qualifiy this OP by saying the wind is blowing a 190 ft/sec, then that could be a different story, but still not primarily due to the ambient temperature.

But then again, I may not know anything about this either, so … :slight_smile:

29

Wait. Do that again using real units…degrees K!

30

Are you jesting? I can never tell here! If it would really help, I will redo in C/K vs F/R. But I’m pretty sure you know that they are equally absolute measurements of temperature. :slight_smile:

31

  1. Yes, water puts out a fire by taking away heat. Water has a ridiculously high specific heat (the amount of energy it takes to raise the temp of water), and so will absorb heat like mad from a fire.

  2. What the hell is R?

32

Either I am getting way too old for this or you who have questioned this have never taken a thermodynamics course in the US, really don’t know. Both are equivalent! 0K (Kelvin) is -273C and 0R (Rankine) is -460F, e.g. 0C = 273K and 32F = 492R. Hope this helps – DD

33

When I first saw the title of this thread, I thought it was about a water additive for firefighting ( http://www.firefreeze.com/ )

Regardless, we’ve been through this before (with all due regards to stuyguy), and I’ll try to work through it again.

First, some very basic fire science stuff (I taught this to three 5th grade classes last week). We’ve all been taught about the Fire Triangle, you need fuel, heat, and oxygen for a fire to start. The one that the public isn’t taught about (but we teach in the fire service) is the Fire Tetrahedron: fuel, heat, oxygen, and an uninhbited chemical chain reaction. Too little of any one of these four, and the fire goes out. A balance is needed between the four elements. Also, you can start a fire with the Triangle, but you need the Tetrahedron to sustain it.

With that in mind, lets look at a fire (this is very generalized…I don’t have the energy to go into the minute details).
We have a small fire at the end of the cigarette. When we start it, we have the fuel (the cig.), the oxygen (ambient in the air) and the heat (first from the match/lighter, then generated from the fire itself). Once sustained burning begins, toss in the uninhibited chemical chain reaction that keeps it going.

Now, take this small fire at the end of the cigarette and move it into a cold (but tolerable by the smoker) enviroment. The cigarette is still going to produce enough heat to maintain that chemical chain reation. More heat is going to be lost to the enviroment through radiation and convection (not too much by conduction) since the air around the fire is colder, but its not going to be significant.

Now, instead of the cigarette being in a human-tolerable cold enviroment, put it in an ungodly cold enviroment. We’re talking -300 F here (thats a complete WAG, but you get the idea of freakin’ cold). Get down that low, the fire will lose so much heat to the enviroment that it no longer has enough heat* to feed back into itself and allow combustion continue.

I don’t have numbers to tell exactly what temperature that fire is going to go out at. Its going to depend on the rate of heat release of the fuel, available oxygen, air currents around the material, distance to nearby objects, and of course the ambient temperatre, amongst other things. But, cool down the enviroment around the fire enough, and the fire will go out.

While I’m here…
Surgoshan, there are 4 ways to put out a fire: remove the heat, remove the oxygen, remove the fuel, or interrupt the chemical chain reaction. Water removes the heat, CO2 removes the oxygen, removing the fuel is used in forest fires (firebreaks), dry chemical and halons interrupt the chain reaction. Pretty easy, huh? :slight_smile:

  • The heat from the fire heats up the fuel, pyrolizing the material into combustible vapors. If the fire can’t produce enough heat to continue pyrolosys (that spelling looks wrong, but I’m too tired to look it up), the fire’s going to go out.
34

We certainly can make this hard by considering ever possible effect known. Or, if I understand the problem, could someone have a cigarette at sea level on a nice, clear, calm evening in Anartica at -129F? And to simply the problem, how would it differ from having a cigarette at sea level on a nice, clear, calm evening in Chicago at 0F or 32F. Of course if someone here has smoked a cigarette in Anartica at -100F, maybe they could comment and make short order of this problem.

The problem would then reduce to, does this change in the ambient temperature from Chicago to Anartica, cause the cigarette to go out? What effects due to this change are significant and are they sufficient to extinguish the combustion. This would seem to involve primarily, dX/dT, oxygen concentration, adiabatic temperature (internal energy(@T) vs chemical Hr) and/or reaction kinetics (concentrations vs k[T]), delta heat transfer, maybe even in that order. Not nearly as difficult a problem. But then if I don’t understand the OP … :frowning:

35

Doubt this helps the discussion much, but I have smoked a cigarette outside at -50C in the Arctic. Subjectively speaking, the cigarette burns much faster, since the smoker is in one helluva hurry to get back inside.

Anecdotal research in my area (Arctic, not Antarctic) seems to indicate that in recent history, there have been no conditions in which people have been unable to have a smoke.

In the interests of science, I would be willing to help test this, if anyone cares. However, weather conditions will not be optimum until the end of January/beginning February. And if we have a warm winter, it may not get much past -40C.

We are just testing in ambient temperatures, right?

Tisiphone

36

The burning tobacco (cherry) of the cigarette ignites the tobacco closer to the filter using the heat of the cherry. If the not yet ignited tobacco of the cigarette - the tobacco closer to the filter were so cold due to ambient temperature I suppose the burning cherry may not produce enough heat to ignite any more tobacco.
In other words, I suppose it could be so cold that an ignited cigarette may not continue to burn; but as long as there is oxygen and fuel a fire will continue to burn. Unless acted upon by another consideration like wind blowing out a match or water extinguishing burning paper.
Although, in the Fire Protection Engineering field, there is a recognition that fire will pretty much do as it damn well pleases - which makes arson investigations that much harder for us.

37

**KCB615 wrote:

Now, instead of the cigarette being in a human-tolerable cold enviroment, put it in an ungodly cold enviroment. We’re talking -300 F here (thats a complete WAG, but you get the idea of freakin’ cold). Get down that low, the fire will lose so much heat to the enviroment that it no longer has enough heat* to feed back into itself and allow combustion continue.**

One thought. LOX (liquid oxegen) is used at the oxidizer in rocket fuel. I’m not an aero-space engineer (nor do I play one on TV :slight_smile: ) but I assume the liquid O2 is delivered into the combustion chamber still in liquid form, where it ignites with the fuel and BLAM another rocket into space.

Therefore, you can get down to pretty cold temperatures and still have fire?