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Today, most animals in slaughterhouses are killed by CO2 poisoning. That's thanks to the HSA (Humane Slaughter Association) and similar organizations.

Critics of HSA, including but not limited to BiteSizeVegan, claim that killing animals via CO2 is not humane, that being exposed to high levels of CO2 causes the feeling of suffocation and burning of the eyes.

However, one student at my university is developing a low-cost electronical device for detecting elevated levels of CO2 for his bachelor thesis. He says that human beings can't detect lethal levels of CO2, that countless people have been exposed to lethal levels of CO2, mostly in the wine industry, and that many have died that way.

So, who is telling the truth here? I can imagine that both of them are true, that perhaps if you are exposed to air with 2% of CO2 for hours you die without feeling anything, whereas animals in slaughterhouses are exposed to around 70% CO2, which they can and do feel. However, I have no evidence for that.

FlatAssembler
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Hypoxia is notoriously difficult to detect post-mortem, which indicates that it doesn't cause damage per se: the brain shuts down first.

Generally, CO2 >10% is considered lethal (for humans), and at these concentrations it causes death due to its own toxicity. If I were to bet, this is more likely to be painful than high concentrations like 70%, which work mostly by displacing oxygen, causing very quick brain collapse.

Hypoxia due to oxygen deprivation is very well studied: it regularly kills pilots, miners, etc. It is so insidious exactly because we don't feel anything. It doesn't cause sensation of suffocation (provided that pressure is reasonable). Only by high conscious effort can we detect the onset of hypoxia. Pilots are trained for this and still die from time to time, or cause incidents.

Zeus
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  • The source you linked has little to do with my question, and so does your answer. – FlatAssembler Sep 29 '23 at 12:33
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    @FlatAssembler, true, but I doubt there is [correct scientific] research that does. Nevertheless, everything we know about this condition suggests that the death is painless. It starts from complete loss of consciousness. Or in other words, there is (likely) no evidence that "death by CO2 poisoning is painful", nor a strong reason to believe so. If somebody finds it, welcome. – Zeus Sep 29 '23 at 16:09