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In my story, I have need of a gas or gaseous compound that will knock out anyone who inhales too much of it and then kill them if they don’t reach clean air in a few minutes. I know of many gasses that are lethal upon inhalation and others that knock you unconscious upon inhalation, but is there some sort of substance that will knock you out then kill you?

Time is a factor here and ideally I need my characters to pass out within minutes of inhaling a concentrated amount of the substance, but death can come however fast after the initial inhalation. To get an idea, I would like my characters to be dead within fifteen minutes of inhalation in a concentrated amount.

Is there anything we know of in real life that fits under this description?

(Side note: I wouldn’t be too upset if it weren’t, but if said gas were flammable that would be amazing :p)

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closed as off-topic by sphennings, Aify, Vincent, JBH, L.Dutch Nov 15 '17 at 3:47

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about worldbuilding, within the scope defined in the help center." – sphennings, Aify, Vincent, JBH, L.Dutch
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Carbon monoxide works that way, and there are many other gases. $\endgroup$ – Alexander Nov 15 '17 at 1:36
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    $\begingroup$ Have you do some research on google? Many gas is lethal when inhaled "too much". Even oxygen can kills you. $\endgroup$ – Vylix Nov 15 '17 at 1:47
  • $\begingroup$ Sydney, the reason this question is going to be put on hold is that it's not about worldbuilding. It's a question about our real world. Those are off-topic beause there are plenty of places that can answer such a question. Thanks! $\endgroup$ – JBH Nov 15 '17 at 3:44
  • $\begingroup$ I'm not sure how this question isn't about worldbuilding. Granted, it's not a good question, but it's about worldbuilding nonetheless. We do have plenty of other questions like it. $\endgroup$ – HDE 226868 Nov 15 '17 at 3:58
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This might sound silly, but the answer is Nitrogen.

Nitrogen gas (N2) is (almost) inert and doesn't actually affect people at all at sea level pressures. We breathe it all the time and it's the single most common element that will ever enter our lungs. What it does is 'dilute' the concentration of oxygen entering our lungs to levels that don't burn out our lungs or introduce oxygen toxicity (this is why scuba divers have to use thinner O2 mixes at deeper levels because the density increases the ACTUAL O2 entering the bloodstream).

Let's say you find a way for the nitrogen 'mix' to be increased as a percentage in a particular space. What you'll feel is a bit drowsy at first, but you won't notice anything wrong with your breathing. It will take some time but effectively you'll suffocate through lack of oxygen, but you'll be breathing pretty much normally through to that point. I'm not sure the exact numbers of how long you can breathe close to pure nitrogen before passing out, but it's not like you'd be holding your breath because at first, you wouldn't even know anything was wrong. Additionally, nitrogen in levels slightly higher than can be achieved at sea level pressures has a narcotic effect, which means that it's even harder to think clearly.

This approach works great on space ships, where suffocation doesn't involve adding a new compound, merely restricting the important one.

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Carbon Monoxide

It's a colorless, odorless gas often created by the incomplete combustion of hydrocarbons. It is heavier than air, so it tends to pool in low places.

It kills lots of people every year, frequently in basements and other places where the low point in the dwelling is also where the gas fired heater is also located, or where a wood stove heater, or whatever else is used to heat the house.

Here is why it's so nasty. Since it is heavier than air, it pools and displaces the good air up over time. You can't smell it, so you have no idea. It also has a single carbon and single Oxygen atom, so it will bind with hemoglobin in the blood, and if I am not mistaken, it gets a better bond than oxygen. the body can't use the Carbon Monoxide, but since a gas exchange is happening, the bodies hypoxic drive to breath is dulled down.

The victim will probably get a headache, followed by sleepiness, then they will pass out. Once they pass out, they will likely be dropping into an area of an even higher concentration of Carbon Monoxide. Death follows shortly after. Victims of this kind of poisoning will frequently have bright red lips, due to the color of hemoglobin when bound with Carbon Monoxide.

If you get a person out before then, they are still going to be messed up for a while. It takes a while for the Carbon Monoxide to get out of their system. In particularly bad cases, a hyperbaric chamber is needed to knock the bonds to the hemoglobin loose.

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    $\begingroup$ Also, relevant to question but not mentioned, carbon monoxide is kind of flammable in that it burns fairly well (oxidizes to carbon dioxide). But the ignition point is kind of high, which is why it can escape slow burning fire. So it isn't really flammable, but can be in a specific circumstance. Which might be enough. $\endgroup$ – Ville Niemi Nov 15 '17 at 2:22
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    $\begingroup$ @VilleNiemi I don't know the flash point of CO, but I know its high. One of the features of the wood stove in my basement is that it has a sort of secondary burn chamber that makes it much more efficient, but you have to get the whole thing hot enough for the spit on thick cast iron to sizzle before you open the second chamber. Once the second chamber is going, the CO risk is supposed to drop severely, and the heat output goes WAY up. 185 sq meter (2000 sqft) house can be kept at 30 deg C (85 F) while outside it's -23 C (-10F) outside. $\endgroup$ – Paul TIKI Nov 15 '17 at 2:33
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    $\begingroup$ I think it is somewhere between six and seven hundred degrees centigrade. So as I said, not really flammable, but can happen in special circumstances. $\endgroup$ – Ville Niemi Nov 15 '17 at 2:50

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