alt Hacker NewsAir 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.
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.