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On Pandora, humans have to wear oxygen masks when moving about in the open air. On arrival, the soldiers are told, "you lose that mask you're unconscious in 20 seconds, you're dead in four minutes." This suggests that the death occurs from suffocation rather than poisoning. I'd assume the suffocation results from an oxygen concentration that is lower than humans require.

The wiki says the air is toxic containing gases such as hydrogen sulfide. Wouldn't this kill a person faster than suffocation?

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  • See also scifi.stackexchange.com/questions/32511/…
    – Andrew Thompson
    Commented Mar 18, 2013 at 5:05
  • This question is not a duplicate. The question referenced asked why the atmosphere is so toxic. This question asks about specific effects of that toxicity on humans. Apples and oranges !
    – Stan
    Commented Mar 18, 2013 at 20:59
  • the entire movie is a propaganda piece for the AGW lobby and their perverse obsession with CO2 being a toxic pollutant. Of course they had to generate a planet where CO2 was shown to be toxic to humans, so they created one with levels many times higher than on earth, hoping people will think "wow, we have to reduce our CO2 emissions or we'll kill ourselves".
    – jwenting
    Commented Mar 19, 2013 at 8:14
  • Related: Why were the humans unable to breathe the air in Pandora?
    – TARS
    Commented Oct 14, 2016 at 10:10

2 Answers 2

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The oxygen concentration and pressure are suitable for humans. It's the high concentration of Carbon Dioxide and Hydrogen Sulfide that cause problems. See Exopack

Carbon Dioxide binds to human red blood cells as part of normal metabolism here on Earth. However, given the low concentration in our atmosphere (<.04%) it poses no problem especially in comparison to our Oxygen concentration (~21%). When Carbon Dioxide concentrations get about 4% (Pandora is 18%) that decreases the amount of Oxygen that binds to blood cells leading to Oxygen deprivation and asphyxiation.

Hydrogen Sulfide is a hemotoxin. It forms an irreversible complex bond with the hemoglobin in red blood cells destroying their ability to bind with and transport Oxygen. This also leads to cellular Oxygen deprivation. The concentration on Pandora is > 1%. The Pandora page states that concentrations greater than 1000 ppm (0.1%) can cause immediate collapse even after a single breath. And we're talking a 1% concentration, 10x greater. I think your point is well taken. If Hydrogen Sulfide really is present at a 1% concentration, it's bye-bye rather quickly. You wouldn't have to wait for asphyxiation due to the excessive Carbon Dioxide. With that said, it's all Oxygen deprivation of one form or another so you could consider it suffocation.

Additional references here's a Hydrogen Sulfide Toxicity Chart & Carbon Dioxide Toxicity Chart

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  • I didn't know how lethal CO2 can be! Always thought carbon monoxide was the one to watch out for.
    – KalenGi
    Commented Mar 21, 2013 at 14:37
  • You got something wrong there. Carbon Dioxide doesn't bind with the blood cells. It does something with your nerves but can't remember exactly what. However carbon monoxide does what you described.
    – Clayn
    Commented Oct 14, 2016 at 7:40
  • @KalenGi Both are dangerous, it's just that CO2 hurts like hell (Carbonic Acid buildup is why holding your breath for so long hurts) while CO just makes you tired (but you won't wake up if you keep breathing it). Gotta watch out for CO because you won't notice it (CO2, you'll notice. Rather quickly.)
    – Delioth
    Commented Oct 14, 2016 at 20:29
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The collapse would be due to the high carbon dioxide concentration, which is greater than 18% according to the Avatar Wikia site. At that concentration under Pandora's 0.9 Earth standard atmospheric pressure, more CO2 would be diffusing into your bloodstream than out of it. I can't say whether you'd hit the deck in twenty seconds, but that much CO2 would certainly wreck the calibration of the body's oxygen transport system and kill a human in short order.

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