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Comment by 1e1a | Hacker News Reader

It looks like they are actually using nitrogen: https://youtube.com/watch?v=22rvpUecLts&t=1134s

Air is mostly nitrogen, about 80%. Pure oxygen as you might be thinking, would be quite dangerous - not only for long-term consumption but also in terms of its effects. Oxygen is fuel for fire so a 100% oxygen environment would quite create the pyrotechnic show! The 'white' you see from the exhaust isn't the exhaust itself - nitrogen is obviously colorless, but the moisture in the surrounding air freezing. It's going to be coming out quite chilly to keep the nitrogen liquified ( boiling temp of something like -196F).

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Whoa, was just watching the video (great link btw). People have been debating the specs, but they're shown unambiguously right here. [1] It has 95 kn peak thrust, 6g peak acceleration, pressure of 5500 PSI, and a min operating temp of -200F.

[1] - https://youtu.be/22rvpUecLts?t=1339

Of course air is mostly nitrogen. But if you replace 10% of the air with pure nitrogen you go into OSHA-angering levels of oxygen depletion, and if you replace 25-30% you get into serious danger.

Not easily achieved in a tunnel, but much more easily achieved in a garage.

10% of the air replaced with pure nitrogen would be 0.8 * 0.9 + 1.0 * 0.1 = 82% nitrogen, 18% oxygen. That's perfectly safe for brief exposure, which is all it would be before you return to ambient levels.

To create a dangerous scenario you've gotta do something like somehow gas out your entire tank in a garage and then just stand around for a while breathing it in. Kind of an improbable scenario unless somebody is trying a really weird suicide attempt.

The bigger tank apparently holds 250kg of air. That's about 200 cubic meters. A two car garage is likely less than 100 cubic meters.

You wouldn't need to dump nearly an entire tank of nitrogen to reach levels that are immediately dangerous. And oxygen deprivation makes you stupid well before it makes you pass out, with no "lack of air" panic since that is based on CO2 levels, so even when it would be survivable for a couple minutes you might not even think to escape.

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