Well, there's a low grade vacuum outside so you probably don't want to.

It's a failure of the onboard steam tanks that scares me. ("The steam is stored onboard until reaching the station. Water and steam tanks are changed automatically at each stop")

I don't want to think about what the result of that would look like for the cleanup crew. Eeeewww.

It's a big self-contained pod, they'd just pull it off the line and bury the whole thing.

Well the pod might contain the steam initially, but I doubt it would be engineered to survive the increased heat and pressure for very long.

They're just gonna have to send in a crew of astronauts to chisel the freeze-dried human stew off the inside of the tube.

I really doubt the steam tank will be inside the pressurised volume. If they fail they would vent overboard. While an explosive failure would probably cause problems it wouldn't expose the passengers to high pressure steam.

The failure mode for composite overwrap pressure vessels is a slow leak, due to the overwrap containing the metal.

A vehicle near the end of its ride will be carrying up to 818 kg (1800 lb) of superheated steam (127 C, 260 F). The 4000 kg (8,900 lb) of onboard batteries and 1800 kg compressor will be dumping heat too. This is 6600 kg of "hot stuff", whereas the entire capsule is projected to have a mass of 15000 kg.

The current design has the passengers in an enclosed capsule in between the compressors and the batteries, with a pressurized air channel running right down the center isle.

Keeping the cabin cool will be a challenge. If that emergency braking is activated, it could get a little warm in there before they are rescued.

I think they may have to quickly repressurize the loop if a car ever gets stuck.

I wonder why they do not use ice. Melt it as a heat sink in normal operation, and vent it to the tunnel for emergency evaporative cooling.

Room-temperature water is readily available, easier to handle, and works almost as well.

The output of the compressor is at 1000 deg. F and 300 psi. That is pretty scary.

The combustion temperature of JP-4 is 3,688 °C.

Sure - but that is happening dozens of feet away inside a can designed to contain it. This extremely high temperature and pressure air will be flowing right under your butt. Serious question, Is any kind of breakthrough in insulation needed?

Well, if the can fails you're toast either way. :-)

The pressure ratio for the compressors in the CFM56 engines in current model 737-800 models is 32.8:1, so somewhere in the neighborhood of 400-500 psi (will depend a lot on altitude).

Seriously, we've been building machinery to operate safely in this pressure and temperature range for a long time.

Yes, and it involves a lot of the considerations we're bringing up here.

Engines do fail on passenger jetliners from time to time. There are numerous stories of planes landing safely after an engine catches fire. But the plane is travelling at a good speed through the atmosphere. How would things be different in a much smaller vehicle sitting stationary in a mild vacuum?

How would passengers escape a battery fire? (as has been seen multiple times on very modern jets)

If the tube had to be repressurized in an emergency, how long would the tube be out of service to be pumped back down again?

Is it worth building a three tube system for such a possibility?