Why don't cats, small dogs and other small pets protect us like a canary in a mine?

[Francis_Vaughan]

Gas movement in and out of the blood is an equilibrium mechanism. This is good and bad.

If you are in a high CO[sub]2[/sub] environment the blood can’t get rid of its CO[sub]2[/sub] load, and you get distressed quickly. Even higher concentration in the air and the levels in your blood can rise fast because you are taking it in, as well as generating it from normal body operation.

But low oxygen levels are really nasty. Once the partial pressure of oxygen drops below a critical level the oxygen level in the blood will drop to another critical point - a point where the exchange of oxygen from the blood into the living cells stops. This level is not zero (about 80% from memory). And it is approached rather precipitously. Even with some oxygen in the air, useful respiration will stop entirely. You will go unconscious within seconds.

Bird blood has a lower affinity for oxygen. I suspect that this critical concentration is directly related to the affinity, and thus birds reach the point of zero useful respiration at a higher oxygen partial pressure than humans.

[Some_Call_Me.Tim]

@Machine_Elf

I am directly aware of one incident in which an individual entered a room in which a CO2 fire suppression system had just been activated.

He was quickly rendered unconscious.

His coworker, aware of what had happened, entered the room to try to drag the victim to safety. the coworker was nearly rendered unconscious, and had to retreat to fresh air before going back to finish dragging the unconscious victim to safety.

It’s not that you don’t know you’ve inhaled a lungful of pure CO2 - it’s that once you do, your brain can be rendered hypoxic so quickly that you can’t reach safety before lapsing into inebriation and then unconsciousness.

The problem in these cases isn’t particularly CO2 poisoning/hypercapnia, which takes some time. Instead, hypoxia is the killer.

The thing is, unlike CO or other atmospheric poisons, humans have pretty decent excessive CO[sub]2[/sub] detectors. So in the scenario in question of humans + dog walking down into a cave with too much CO[sub]2[/sub] there would be a gradient and they’d notice once when the CO[sub]2[/sub] had increased to uncomfortable levels as they walked. Uncomfortable levels are considerably below dangerous levels.

This doesn’t work in, say, a nitrogen atmosphere, where you can fall unconscious without noticing. Humans can’t naturally detect a lack of oxygen.

[Francis_Vaughan]

I think the point here is that with lots of CO[sub]2[/sub] in the air the problem ceases to be hypercapnia, with hypoxia becoming the dominant danger. You might become distressed with the high CO[sub]2[/sub] levels, but the very low oxygen levels are already about to kill you. There becomes a very fine line between realising you need to get out, and being unable to do so.

[DesertDog]

@crucible

I just shake my head each time a new weekly 40# bag of cat litter arrives on my son’s porch from Amazon, wondering how the drones are going to manage that.

Perhaps two of them could manage it by suspending it on a bit of string between them.

[TimeWinder]

@Chronos

If a cat is lying still, it’s probably asleep. Yeah, if you looked close, you might notice it’s not breathing, but you wouldn’t look close if it was sleeping under the couch, or behind the drapes, or just in another room.

Or just because you were already suffering effects yourself, which include confusion, sleepiness, and reduced cognition well before the lethal dose.

[Melbourne]

@iamthewalrus_3

Cite that this happens? The hypercapnia response, which is what feels like suffocating, is triggered by excessive carbon dioxide in the bloodstream.

There are lots of gases that you can suffocate on without noticing if you start breathing them and not oxygen because you don’t actually notice hypoxia. CO2 isn’t one of them. Someone going into a high CO2 atmosphere should immediately feel like they can’t breath and try to get the fuck out.

It was a “known” hazard of caving when I was a boy. Apparently, sometimes lower levels of caves fill up with higher levels of CO2 (possibly acidic rainwater in limestone caves contributes to the problem). We weren’t taught that people automtically recognised the nature of the problem and excaped: cometimes you are already doing heavy exertion while you’re scared breathless.

[iamthewalrus_3]

To all the people who responded to my requests for a cite, thank you for the additional explanations. I’m satisfied that this is a real danger.