Carbon Dioxide & Methane

Carbon Dioxide (CO2) is a byproduct of respiration for both human-like and aquatic aliens, and must be managed by systems to remove it from the environment before it poisons the aliens aboard the station. CO2 is also produced by fires.

In Hydrogen atmospheres, the byproduct of respiration is instead Methane, which likewise needs to be removed before it poisons the aliens in those areas.

Similar to Heat, "supply" represents how much of the gas the station can remove, while "demand" is how much is generated. And similar to Water, excess takes more time to kill NPCs; unlike Water, they remain unaware for some time, until symptoms (and thus unhappiness) appear suddenly shortly before death. Excess CO2/Methane also rapidly accelerates suffocation if Oxygen/Hydrogen supplies are short.