Against a character, vacuum damage possesses the armor-piercingThis quality applies to weapon damage, reducing damage reduction. (all) quality; against all other targets, it does not. Some gear is resistant to vacuum damage.
A character subjected to a vacuum suffers 5d6 lethal damage per round. This damage does not drop over time unless the conditions producing it change (e.g. a character reaches an area with pressurized air). During the first round only, a character may make a Fortitude save (DC 15) to reduce this damage to 1/2 (rounded down). The GC may determine that an area of extremely low pressure inflicts between 1d6 and 4d6 vacuum damage per round, but this is quite uncommon.
A character suffering from vacuum damage simultaneously suffers from suffocation.
Vacuum damage inflicts only one type of critical injury — each time a character suffers 25 or more points of uninterrupted vacuum damage from a single source (even if the damage is applied over time), he must make a Fortitude save (DC 15). With failure, he suffers 1 point of permanent Wisdom damage (i.e. brain and sensory damage).
Each character who loses 1 or more vitality or wounds to vacuum damage also suffers 1/2 as much stress damage (rounded up). A standard character suffers this stress damage each time he makes a Damage save against vacuum damage.