Stoves, Tents and Carbon Monoxide – Deadly or not?

[Cat Jasins]

Companion forum thread to:

Stoves, Tents and Carbon Monoxide – Deadly or not?
Part 1: Theory

[Michael von Gortler]

This excellent article also reminded me of the story of Commander Robert Byrd who spent some time alone near the South Pole. He was in a small hut and nearly succumbed to CO poisoning that was occasioned by snow blocking the flue vent for his indoor warming stove/cookstove.
Boulderman99

[Dale Wambaugh]

Were measurements of CO made at different places in the tents? The photo shows the meter next to the stove– I wonder if pockets of gas are formed in a tent, where a person sitting up may get a very different exposue that one laying down, dending on air circulation and/or the tendency of the exhaust to rise or fall.

[Roger Caffin]

Hi Dale

> Were measurements of CO made at different places in the tents? The photo shows the meter next to the stove– I wonder if pockets of gas are formed in a tent, where a person sitting up may get a very different exposue that one laying down, dending on air circulation and/or the tendency of the exhaust to rise or fall.

I missed your question – sorry.
This Part 1 of the series covers the Theory of why CO might be emitted. Part 2 will cover the testing of the Theory, and this is done under controlled conditions in an instrumented Test Chamber. Subsequent Parts will cover the testing of a whole range of stoves using all sorts of fuels. Finally we will cover the testing of some stoves in tents in the field.

We are doing it this way because, really, trying to control the test conditions in a tent in the field is almost impossible. But once we know how the stoves perform under controlled conditions we can then look at field tests with much more understanding.

What conclusions will be drawn? Well, you will have to read the following Parts of this Series, won’t you? :-)

But I can say here that we now have a real understanding of what causes CO emission and how to handle the hazard. Not all stoves are equal …. but some are very good.

Cheers

[Tony Beasley]

Hi Roger,

When is "Stoves, tents and carbon monoxide- deadly or not" part 2 going to be published.

Tony

[Einstein X]

Probably a bit late to respond but my attention to this article was drawn after the second part came onto the homepage, so i read this one first.

Roger,

In the table you show how the different carbon-hydrate chain molecules cobine with oxigen to create CO2 and H2O. If i count the number of molecules before and after the reaction i noticed that Propane has 3 C, 8 H and 14 O molecules before the reaction, after the reaction there are 3 C, 8 H and 10 O molecules. After reaction there are 5 O molecules missing for Butane and 6 for Pentane, etc. Now i assume that the 'missing' O molecules form harmless O2 molecules, but to me it seems that there are too many O molecules before reaction.

Could you explain why, in the case of (say) propane there are 14 O molecules required before reaction? It would seem to me more logic that the reaction is like:

C3H8 + 5 O2 => 3 CO2 + 4 H2O

Eins. On to part two.

[Mike Cecot-Scherer]

Hi Roger,

Enjoyed your Part1 of the winter stove quest but have found a rather serious mistake in your referenced carbon monoxide article.

Carbon monoxide in camping stoves is caused by exhaust getting into the intake by recirculation currents.

You can easily test this:
1) put an empty pot on the stove, let it get red hot and see if the CO stops
2) deliberately cause some recirculation with an obstruction and see if the CO goes up

I got this information from a Professional Engineer that specialized in forensic reconstruction of combustion events (usually for for use in lawsuits). BTW a Professional Engineer in the US is a multi-disiplinary engineer whose passed quite a gauntlet to be certified.

Exhaust recirculation also can be seen to be a factor in hanging stove or lantern CO creation as both types form an exhaust pool at the roof from which some can easily get back down to the intake. It also conjures a nightmare scenario where someone operates a stove in their tent beneath a gas lantern – CO in knock-you-out-and-kill-you doses could be quickly produced.

Best,
Mike Cecot-Scherer

[Roger Caffin]

Copied from the discussion at http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=79177&skip_to_post=674764#674764

> Carbon monoxide in camping stoves is caused by exhaust getting into the intake by recirculation currents.
I have to disagree with you here. Carbon monoxide results from incomplete combustion: that's basic chemistry.

For there to be incomplete combustion one of two conditions have to apply: flame quenching or insufficient oxygen. In the case of a small camping stove being run in open air or with adequate ventilation, I find it hard to imagine that 'inadequate oxygen' could apply.

> He QUITE disagrees with the cold pot quenching theory of CO production.
Tough. He needs to learn some basic chemistry.

> I got this information from a Professional Engineer that specialized in forensic
> reconstruction of combustion events (usually for use in lawsuits).
Sigh. Meaningless, and valueless.

My wife was on a jury once in a lawsuit about an injury. Both sides had qualified/certified engineers as technical witnesses. The two engineers testified radically differently: one had calculated that the forces involved were X (within OSHA limits) while the other had calculated that they were about double that (well outside OSHA limits). They could not both be right.

Later on I sat down and did the full analysis myself and I could see what each guy had done, and why one of the QUALIFIED engineers was wrong. 'Experts' have been wrong before.

> You can easily test this:
> 1) put an empty pot on the stove, let it get red hot and see if the CO stops
I have done that test many times, with continuous measurement. Yes, when the cold metal in the flame gets red hot the CO production often drops to ~0. Except when the stove is something like a Reactor, for which there is no hope.

> Exhaust recirculation also can be seen to be a factor in hanging stove or lantern
> CO creation as both types form an exhaust pool at the roof from which some can
> easily get back down to the intake.
Abstract theory, and using a false premise.
Practice is that the hot air circulates, and can be seen to drift out of the tent door. (Steam goes with it – makes a good photo with a flash.) If the tent was sealed and there was no wind at all, then you would have a real danger. But under such conditions who seals a tent up?

Sorry, but your theory does not apply to small camping stoves being used in bad weather.

Yours
Roger Caffin (BSc Hons, MSc, PhD, consultant research scientist)

[David Thomas]

Oh, can I join the fray? Even if I'm a PE? And a chemical engineer?

Quenching definitely happens on cold surfaces. It's why modern auto engines aren't "long stroke" and are often "over square" (shorter, squatter cylinders) – to reduce the surface area and the quenching that occurs on the cylinder walls. And those cylinders walls are hotter than even a pot of boiling water, much less a pot of snow.

Imbalanced air-fuel ratios in stoves, internal combustion engines and many other devices can cause CO production if too rich in fuel. A few of many possibilities on that front:

– a too-large fuel orifice

– a too-small / too-restricted path for pre-mix air

– low atmospheric pressure due to being at elevation

– lower air density due to hot weather (a smaller effect)

– excess exhaust-gas recycle (EGR is used in automotive engines to decrease peak temperatures and reduce NOx production. But a modern car is measuring O2 in the tailpipe and adjusting fuel injection to maintain 1% O2 to reduce CO).

The bounancy of such hot air is so significant, I'm having trouble imagining a scenario where O2 or CO2 levels in intake air could be significantly effected in BP stove use. Might 1% of the exhaust gases recirculate? Sure and it probably does in a tent. But 1% less O2 happens every time you move 100 meters up the mountain.

Stacking stoves and lanterns vertically would be a way to start getting 10%-20% EGR and that would concern me. Stacking stoves and lanterns is also a way to overheat the upper fuel canister and that's even more exciting. Don't ask how I know. Just don't do it.

[David Thomas]

Rereading the article and the comments again, years later.  “Einstein X” is right.  The stoichiometry shown for the oxidation reactions is wrong. For the 5 hydrocarbons shown, the coefficient for O2 is given as 7, 9, 11, 17, and 25, respectively, but should be 5, 6.2, 8, 12.5, and 18.5.  (if you don’t like the fractional coefficient, double all the coefficients in that equation.  The qualitative point is still completely valid: bigger hydrocarbons need more oxygen to completely combust.  A lot more.

Maybe it’s a regionalism or just a misplaced phrase, but the paragraph, “As an aside, when Australia switched from coal gas to ‘natural gas,’ which is a form of LPG, every stove in Australia had to have either the jet or the whole burner assembly changed. The fuel/air mixture required for safe operation had changed.”  implies to me that LPG is “natural gas” (that 85%-ish methane plus ethane plus other stuff that is piped to your house).  In American usage, LPG = liquified petroleum gas and is mostly propane, boiling off from the lighter ends of crude oil.  “Natural gas” is called that because American cities into the 1940s and 1950s (and Australia until the 60s and 70s) used to distribute “manufactured gas” or “town gas” consisting of vapors driven off of coal by heating it.

Oh, wow!  Two things just connected in my head.  I looked up the composition of town gas and yup, it contains carbon monoxide.  I remember “sticking your head in an (unlit) oven” being a euphemism for (and accurate description of) suicide.  Now, I’ve humanely killed a few critters by asphyxiating them with methane because it’s a nice cheap, oxygen-free gas piped to my house and somewhat of an anesthetic.  But that wouldn’t work in a open oven anymore.  Whereas 60+ years ago, the CO in that unburned town gas could be deadly pretty quickly.

[Author]

Posts