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Comment by ovi256 | Hacker News Reader

> storing a lot of dense, pressurised CO2

In my understanding, there's only enough CO2 to use as a working medium in the closed loop. No storage as such.

Still, if it leaks out it will displace a lot of air, just because of how dense it will have to be.

It will, but it's easy for people to detect and needs to be around 10% to kill someone, about a hundred times more than hydrogen sulfide or chlorine or carbon monoxide.

If the baseline is superheated steam, I'm not very worried.

One that, and two, emergency oxygen masks work really well against CO2. It's only toxic at concentrations far above what you notice, not at all toxic at concentrations you clearly notice it (and take care to fix the seat/seal of your oxygen mask), and you shed it very quickly once you get a low-CO2 breathing atmosphere.

It's literally the one thing you don't necessarily need a sensor for if you get regular training to remember how you perceive dangerously elevated CO2.

How is elevated CO2 perceived? Does it have a smell?

Bad air/fatigue. It's the headache/mind-numbing effect you remember from walking into a poorly ventilated classroom or such.

It's not hard to detect, especially if sudden or strong, but to reliably act you need to regularly train to judge actionable concentrations, so you remember the feelings/perception for the specific actionable levels.

When you hold your breath, it's not decreased oxygen that triggers the burning sensation in your lungs and the desperate need for air; it's elevated CO2. So it's pretty easy to perceive if you're at all aware of the signs.

However, reliably detecting 1000~2000 ppm isn't hard, but will require some training.

And that's the level where you want to leave the place in a state that's not dangerous, followed by getting out of there and waiting for someone with an oxygen mask to go leak searching.

But yeah, CO2 is the thing that makes you want to open a window long before acute toxicity.

We have chemical plants all around the world where a leak of one kind or another can (and has) cause a terrible catastrophe. We've gotten to the point where large scale incidents are at least rare even dealing with highly reactive chemicals.

The sudden decompression will cool down the CO2 rapidly. To the point where it will become dry ice. This will slow down the release speed significantly. It is still not nice and probably a risc, but not als large as you estimate.

Actually you can make dry ice like this: get a CO2 cinder upside down and open valve into a cloth bag.

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