Monster Slayer Stan, we are in dire need of your help! The caves in our nearby mountain are filling up with a dense but non-toxic gas that is protecting a monster's nest. The monsters are weak but are hiding deep in the caves. We need you to go in and destroy their nest.

In another world building answer it states that people who breathe in argon have a risk of asphyxiation. With that in mind, how soon would Stan notice the environment was 95% argon? After breathing in that much argon and escaping, how long until Stan can breathe properly again?

  • $\begingroup$ You don't specify the level of technology available to Stan the Monster Slayer. $\endgroup$
    – RonJohn
    Commented Oct 16, 2018 at 19:28
  • $\begingroup$ @RonJohn assume medieval tech, but Stan is a brave fool. He will run in the first time without any preparation $\endgroup$
    – Reed
    Commented Oct 16, 2018 at 19:30
  • 4
    $\begingroup$ @Reed if the Monsters are weak and hiding in their nest in the caves, why do you need Monster Slayer Stan to risk his life to slay the weak monsters who are hiding? Are your people prejudiced against monsters? Is some sort of genocide of monsters happening? $\endgroup$ Commented Oct 17, 2018 at 17:02
  • $\begingroup$ @M.A.Golding the villagers pride their land on its beauty and monsters are all ugly $\endgroup$
    – Reed
    Commented Oct 18, 2018 at 7:04

2 Answers 2


Stan will not notice he is suffocating. He will pass out and die.

Our need to breathe is triggered by accumulation of CO2. High levels of CO2, even with adequate oxygen, will provoke the sensation of shortness of breath and suffocation.

In contrast (for normal healthy people like Stan), if there is not high CO2 you feel no particular need to breathe from progressively lower levels of O2. When your O2 gets low enough you just pass out. This is called shallow water blackout.


Shallow water blackout which occurs when all phases of the dive have taken place in shallow water (i.e., where depressurisation is not a significant factor) and typically involves dynamic apnea distance swimmers, usually in a swimming pool. The mechanism for this type of shallow water blackout is hypoxia expedited by hypocapnia caused by voluntary hyperventilation before the dive. Blackouts which occur in swimming pools are probably driven only by excessive hyperventilation, with no significant influence of pressure change. This can also be described as constant pressure blackout or isobaric blackout.

This happened to me once from breathing helium to make my voice high. I blew out my air and breathed a lungful of helium and talked squeaky. When it was gone I took another breath of helium. Then I came to under a table.

In this circumstance, Stan has argon instead of helium. Argon does fine clearing CO2 out of the lungs and so he will not notice anything wrong. It is a pretty good defense for those monsters.

  • 2
    $\begingroup$ Such a good answer, I deleted my own. $\endgroup$
    – RonJohn
    Commented Oct 16, 2018 at 19:47
  • 2
    $\begingroup$ It is denser than air, so if he's in the habit of singing/whistling while he works he might notice a small change - not sure the 1.5x density will be as noticable as the 5x of SF6 youtube.com/watch?v=d-XbjFn3aqE $\endgroup$
    – JRaymond
    Commented Oct 16, 2018 at 21:28
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    $\begingroup$ If it's denser than air, I wonder if someone could use it to make a cave lethal to creatures like halflings and gnomes but safe for taller ones $\endgroup$
    – Loupax
    Commented Oct 17, 2018 at 7:36
  • 6
    $\begingroup$ Add treasure scattered around floor for extra defense effectiveness against those super-tall heroes. $\endgroup$
    – wondra
    Commented Oct 17, 2018 at 7:53
  • 1
    $\begingroup$ If it is dark inside he might bring a light - maybe a torch. Could this warn him that there is no oxygen? $\endgroup$
    – Risadinha
    Commented Oct 17, 2018 at 19:08

With 95% argon (oxygen can be 5% or can be 0%), Stan would likely lose consciousness within a minute - without feeling any suffocation alarms. If he is somehow brought into the normal atmosphere, it will take him a few minutes to get back no normal, assuming there was no permanent damage to his nervous system.

Inert gas asphyxiation is a more sneaky killer than typical (smog or excessive carbon dioxide) asphyxiation because a person does not feel much until losing consciousness.

  • 1
    $\begingroup$ Also do note that as Stan is a foolhardy monster hunter who is engaged in spelunking, Stan's respiratory rate is probably quite high, which will serve to increase the speed with which his bloodstream is forcibly de-oxygenated. The chances of Stan surviving a brief forray into this cave are essentially 0 unless he was already aware of this possibility. $\endgroup$ Commented Oct 17, 2018 at 1:09

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