Gases are transported, generated, mixed or split via ventilation. Based on Duplicant needs they can be sorted into breathable and unbreathable. There are currently four Unbreathable gases in Oxygen Not Included:
Denoted by a black color, Carbon Dioxide is heavier than Oxygen and will sink to the lowest levels of the duplicants' colony. It is exhaled by duplicants upon consuming Oxygen and as a byproduct of the Coal Generator.