A quick FIRE question

[David Evil Overlord]

A quick question about FIRE.

Fire burns fuel, and needs oxygen. Fire produces carbon dioxide. CO2 is lighter than air, so it rises up above the heavier oxygen, and the oxygen "falls" relative to the CO2, and feeds the flames below.

In zero gravity, the CO2 won't rise above the heavier oxygen, and this will smother the flames like a CO2 extinguisher (only with less white foamy stuff).

Correct?

 

[Fishbowl Helmet]

http://m.io9.com/5779127/how-does-fire-behave-in-zero-gravity

 

[David Evil Overlord]

*places hands in finger-pyramid-of-evil-contemplation*

Excellent!

Thanks, Fishbowl Helmet.

 

[alchemist]

Well, that's what I learned today. DEO and FH - the question and answer team!

 

[David Evil Overlord]

I had a certain plot point hinging on fire behaving a certain way under zero-g conditions. And it works just the way I'd hoped.

 

[Fishbowl Helmet]

I'm a librarian. It's what I do.

 

[Vertigo]

Actually I believe CO2 is heavier than air (I've seen it demonstrated) I suspect it only rises because of the heat.

 

[The Ace]

Thanks, Vertigo - yes coal miners used to test for, 'Black Damp,' (Carbon Monoxide and Carbon Dioxide) by placing a Davy lamp on the floor (ever wonder why electrically-lit coal mines always had a ready supply of the things ?).

If the flame went out, it was time to evacuate.

The Davy lamp also flared in the presence of, 'Fire Damp,' (methane) long before it reached dangerous levels.

 

[David Evil Overlord]

That's okay. As long a a fire gets smothered by it's own CO2 in zero-g, the plotline works.

 

[Mirannan]

One thing that might be worth mentioning:

What applies to flames applies to some extent to living, respiring organisms as well. Which includes humans, and this (among other reasons) means that any vaguely realistic zero-g structure meant for living in would have some sort of ventilation system. This system would have some of the effects of gravity; in particular, it would carry away combustion products and allow a fire to continue burning. The flame would likely look odd to the eyes of someone living in normal gravity, I suppose.

The only way, IMHO, that a flame would go out in the way described in a spaceship or space habitat would be if the fire was in a space not normally inhabited (machinery spaces, maybe?) or if the ventilation system was off line as well - which would cause other, severe, problems for anyone who likes breathing.

 

[David Evil Overlord]

That could work, too.

 

[TheEndIsNigh]

One thing that might be worth mentioning:

What applies to flames applies to some extent to living, respiring organisms as well. Which includes humans, and this (among other reasons) means that any vaguely realistic zero-g structure meant for living in would have some sort of ventilation system. This system would have some of the effects of gravity; in particular, it would carry away combustion products and allow a fire to continue burning. The flame would likely look odd to the eyes of someone living in normal gravity, I suppose.

The only way, IMHO, that a flame would go out in the way described in a spaceship or space habitat would be if the fire was in a space not normally inhabited (machinery spaces, maybe?) or if the ventilation system was off line as well - which would cause other, severe, problems for anyone who likes breathing.

One could argue that an area that contained machinery or something that was likely to catch fire would 'normally' be 'air locked' (IE in vacuum) so that any fire wouldn't have a chance to get going in the first place.

This could be countered by the requirement for cooling so that hot machinery wouldn't just keep getting hot, but I would expect that a machine that was likely to overheat wouldn't be desirable in a space situation. In any case a Nitrogen or CO2 atmosphere would act as a cooling agent and reduce the risk of a fire getting a hold. Having free O2 or air in an area where fire could happen would just leave the spaceship in the position where all it's limited O2 would be used up. The cure would be to seal it off and let the fire extinguish itself. Why risk it. The norm on a space ship should be prevention.

This is common on Earth. N2 atmospheres are often used on drill platforms and other situations where even the smallest spark would spell disaster

O2 could always be introduced into the room if human servicing was required.

 

[Mirannan]

One could argue that an area that contained machinery or something that was likely to catch fire would 'normally' be 'air locked' (IE in vacuum) so that any fire wouldn't have a chance to get going in the first place.

This could be countered by the requirement for cooling so that hot machinery wouldn't just keep getting hot, but I would expect that a machine that was likely to overheat wouldn't be desirable in a space situation. In any case a Nitrogen or CO2 atmosphere would act as a cooling agent and reduce the risk of a fire getting a hold. Having free O2 or air in an area where fire could happen would just leave the spaceship in the position where all it's limited O2 would be used up. The cure would be to seal it off and let the fire extinguish itself. Why risk it. The norm on a space ship should be prevention.

This is common on Earth. N2 atmospheres are often used on drill platforms and other situations where even the smallest spark would spell disaster

O2 could always be introduced into the room if human servicing was required.

Or the people doing the servicing could wear breathing masks. The point is that free oxygen is a constant threat. Incidentally, another reason for filling non-inhabited spaces with inert gas is to prevent corrosion.

I don't think that (without some other good reason) such places as machinery tunnels would be evacuated as a matter of routine. One reason is that such a policy would mean some internal walls having to be just as strong as the external walls of the ship; another is that having large volumes of vacuum inside the ship has a potential for accidents. Another is that vacuum causes other problems, such as needing exotic materials as lubricants, vacuum welding, that sort of thing.

 

[TheEndIsNigh]

Or the people doing the servicing could wear breathing masks. The point is that free oxygen is a constant threat. Incidentally, another reason for filling non-inhabited spaces with inert gas is to prevent corrosion.

I don't think that (without some other good reason) such places as machinery tunnels would be evacuated as a matter of routine. One reason is that such a policy would mean some internal walls having to be just as strong as the external walls of the ship; another is that having large volumes of vacuum inside the ship has a potential for accidents. Another is that vacuum causes other problems, such as needing exotic materials as lubricants, vacuum welding, that sort of thing.

Good points all, although the walls of machine rooms would probably be fairly strong to resist exploding machinery and the like. Plus the ultimate fire damper would be the vacuum.

However, I agree with you, inert atmosphere would be the way to go. I like the idea of breathing masks too. This would remove the likelyhood that if something did go wrong, there would be less risk of blowback when a hot spot was exposed to the air rushing in.

 

[David Evil Overlord]

Thanks for all the input, guys. I think I know how to work this now. The atmosphere will be a serious consideration, along with ventilation.

 

[Glen]

I'm a librarian. It's what I do.

If that line doesn't deserve to have a very special place in a story somewhere...no line does.

 

[David Evil Overlord]

I think I can place that line in my super hero WIP.