[everforward]

I don't think a "leak" would cause decompression sickness. Decompression sickness is caused by bubbles forming when pressure decreases too quickly for the body to expel now-excess nitrogen. A slow, gradual decrease would provide plenty of time to expel excess nitrogen.

A leak in a pressure vessel is basically how deep saturation divers re-acclimate to standard pressure, and they're making a much, much larger change in pressure (maximum of 14.5 psi delta on the ISS, ~429.06 for a saturation diver at 1000 ft). It's really a delta P of 10 psi though, since the American space suits are 4.5 psi. There's not really much point in talking about decompression sickness without a space suit; they'd die of lack of O2 or exposure even without DCS.

Current recommendations for space walks are a 4 hour denitrogenation period breathing 100% oxygen, and that's pretty cautious. That's based on the denitrogenation rate of the slowest tissues; it could likely be done significantly faster without presenting dramatically increased risks of DCS, and especially so if you only need to avoid type 2 DCS where the bubbles present a risk of dying.

[ethbr1]

Also, this is helium from the propulsion system.

>> Helium is used in the spacecraft’s thruster systems to allow the thrusters to fire without being combustible or toxic.

I'm assuming it's used to backfill tanks as they're emptied?

[CableNinja]

Theres 2 use cases:

1) To keep the fuel/oxidizer pressurized and liquid (by pressure) as the tanks content empties.

2) for RCS thrust, as a cold gas thruster.