From Discovered

Exposure to vacuum is survivable for a short time. It causes 1PS/5s exposure. This adds up to 3PS/turn, but the damage has to be soaked 1PS at a time. A normal human will take the 2|Con Passing out after 15s (1|2|PS, 2|Con) and die in 20-30s.

Creatures with +3HF or more may not die from vacuum exposure. They still need some plausible way to power their cells while unable to breathe.