According to this Wikipedia article, cabin pressure is normally maintained at 75kPa. The article suggests that at this pressure it would be difficult or impossible to maintain an open flame due to low oxygen concentrations (supposedly comparable to 15% oxygen in standard conditions). Obviously, things can still smolder, oxidize and overheat, not to mention non-gaseous oxidizers.

My basic question is: could a passenger who smuggled a regular butane lighter past security actually manage to light it after reaching cruising altitude, or would it just produce sparks?

clarification/details: this question from aviation.SE suggests 75kPa is a reasonable minimum, so let's assume that is the exact cabin pressure for this question. so the question becomes, will any mixture of butane, nitrogen and oxygen ignite into a flame if the ratio of nitrogen to oxygen is 78:21 (normal earth atmosphere) and the pressure is 75kPa. if not, then how low does the pressure have to get before the oxygen density is to low to outpace the heat lost to convection?

  • $\begingroup$ I regularly use butane lighters at altitudes from 5000 to 12000 feet. They work fine. Passenger airliners are pressurized to ~6000-8000 feet equivalent altitude. So, yes it will work just fine. $\endgroup$ – Jon Custer Sep 14 '16 at 13:48
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    $\begingroup$ (As a total aside comment, most smart phones have a pressure sensor and apps to give you the readout in feet or meters above sea level are readily available. So, while sitting on a plane you can see for yourself. Apparently, different airlines set it differently, but an estimate of 6000-8000 covers most of them. Above that some people will get in real trouble, below that is just a pain.) $\endgroup$ – Jon Custer Sep 14 '16 at 13:57
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    $\begingroup$ I remember when commercial flights used to have a smoking section in the back of the cabin. $\endgroup$ – Solomon Slow Sep 14 '16 at 14:39
  • $\begingroup$ A side note. The flame should be larger than at sea level. Liquid butane and the gas over the liquid is relatively low pressure and nozzle velocity is subsonic at sea level. Therefore no choking. So with the downstream pressure lower at altitude you would expect an increased mass flow rate. So the flame might also be less efficient (fuel rich) producing additional soot. $\endgroup$ – docscience Sep 14 '16 at 16:51
  • $\begingroup$ But is the nitrogen:oxygen ratio the same in an aircraft as it is at sea level? $\endgroup$ – Myridium Sep 14 '16 at 17:27

Yes you can. The vapor pressure of butane is (according to Wikipedia) 170kPa. Your difference in pressure becomes 170kPa-75kPa=95kPa. On that note, atmospheric pressure is 101kPa. The difference there is ~70kPa. As you can see, the butane will escape from the lighter more easily on the airplane. As for the oxygen composition in aircraft cabins, I wasn't able to find any data. I suspect that the percentage difference has a negligible effect on lighting a lighter.

  • $\begingroup$ i had no doubt that the butane would vaporize, my concern was that the oxygen density per square centimeter would be too low to maintain the plasma necessary for a standing flame. perhaps i can edit my answer to be more clear..... $\endgroup$ – james turner Sep 14 '16 at 14:55
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    $\begingroup$ In all fairness, you were concentrating mostly on pressure in your question. Now you talk about density of a gas, which is still dependent on pressure. What this comes down to is air-fuel ratio in your question. You will no doubt have a lower AFR under your circumstances. I think what you're asking though, which is a good question, is whether or not the flame would stay concentrated at the source and not dissipate under a lower pressure. FYI, not all flames are composed of plasma. $\endgroup$ – Kjdvlder Sep 14 '16 at 15:52
  • $\begingroup$ i love asking questions on physics.PE because i usually learn more while correcting my question than from the actual answer :) $\endgroup$ – james turner Sep 14 '16 at 16:26

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