At or above the Armstrong limit, exposed bodily liquids
such as saliva, tears, and the liquids wetting the alveoli
within the lungs — but not vascular blood (blood within the
circulatory system) — will boil away without a pressure suit
As mentioned above, we have been boarding planes without pressure suits for decades, and the hyperloop has two security advantages: it has a large supply of compressed air to work with, and the tunnel can be quickly re-pressurized in the event of a severe rupture. A multitude of concurrent failures (much less likely than those in an airplane) would be necessary for a catastrophe.
You got to think that a decompression will happen. Something traveling that fast inside a tube is probable to develope vibrations and material fatigue if something is not working properly (like the compressor or a air cushion), also there can be small parts released from the front pod impacting on the next one.
It doesn´t need to be a huge crash, just a crack on the hull, it will decompress that small pod in seconds.
Also what will happen when of tens of pods traveling that fast, find that there is a sudden recompression of the tube? How fast are they going to stop due to the front overpressure (the compressor is relatively low powered)?. Is not going to be a gentle stop either.
I still think that it´s a great idea, and that there will be ways of solving those problems, but it´s going to be difficult and require lots of R&D.
Obvious engineering issues for further investigation. I would just point out that fatal failure mechanisms can be pointed out in any transportation system. The acceptance criterion is a sufficiently low fatality rate.
