A room's oxygen level decreases when:
- it contains a breach, fire, or Lanius.
- has a door open to space or another room without full oxygen.
- the Oxygen/Life Support system is unpowered or hacked.
The color of the room indicates its oxygen level -- white indicates maximum oxygen, red/pink indicates lower oxygen, and red lines across the room indicate suffocation danger at 5% oxygen or lower. The Oxygen/Life Support System replenishes and maintains the ship's oxygen, with higher levels speeding up the recovery process and even negating the loss from a hull breach. If the Oxygen/Life Support System is unpowered, the ship's oxygen levels will drop by about 1% every second.
Deliberately deoxygenating rooms has a few uses. Fires in red hatched rooms will be extinguished after a short time, and boarders can be killed by venting rooms, although this technique is unreliable if the Doors Subsystem is not sufficiently upgraded.
Note that certain ships, in particular some Slug ships, have the Oxygen/Life Support system inaccessible to crew (and therefore irreparable), which presents a great opportunity to destroy the system and leave them to suffocate in order to obtain higher rewards.
All Automatic Ships and Lanius Ships have completely vented rooms, meaning that fire-based weapons will be largely useless if the fire cannot be maintained enough to damage the system. Oxygen dependent boarding parties will also find it difficult to damage systems before suffocating.
- A level 1 Medbay will protect crew from suffocation if the ship is completely vented, but it will not regenerate their health. Upgrades to the Medbay can help them recover.
- If a room is totally vented, opening a nearby un-vented room will speed up oxygen recovery.
- The Crystal race takes considerably less damage from lack of oxygen.
- The Lanius race deplete oxygen where they are and takes no damage from lack of oxygen.
- Improved Life Support System can significantly delay oxygen loss caused by breach and Lanius crew.
- Advanced Life Support System can even fill oxygen up in fully vented room which has breach or Lanius Crew, although it takes a while.
- Providing full power to upgraded Life Support System is very useful when your ship is boarded by a party with Lanius, Boarding Drones, and Ion Intruders.
- Improved Life Support is paradoxically rather useful when you wish to save power by not powering Life Support. You can keep the power off for most of the battle, and only refill during a cloak or when it's safer. This can be done with a Level 1 Life Support as well, but the slower oxygen refill rate creates a somewhat larger risk, and required the system will need to be kept on longer to refill, in some cases even after the battle is over.