Solid Oxygen

Oxygen is a light, breathable gas that Duplicants need to survive. It rises above heavier gases like Carbon Dioxide, and Duplicants can breathe it only within a usable pressure range: below 50 g/tile it is unbreathable, while between 50 and 300 g/tile it is breathable but still stresses Duplicants. A typical Duplicant consumes 100 g/s, with several traits reducing or increasing that demand. If a Duplicant cannot breathe, they will hold their breath, stop working, and run for oxygen; if the breath meter empties, they suffocate.

Oxygen is one of the most important early- and mid-game resources because many systems depend on it directly. Atmo Suits, Jet Suits, Oxygen Masks, and Lead Suit Docks all require Oxygen to refill their suits, and the Telescope also needs Oxygen to operate. It is also used in the Oxylite Refinery, which converts Oxygen and Gold into Oxylite at a rate of 600 g/s Oxygen and 3 g/s Gold for 600 g/s Oxylite. In the critter economy, Puft Princes and Dense Pufts can breathe Oxygen and excrete Oxylite, while Longhair Slicksters consume large amounts of it and provide mobile Decor.

There are many ways to produce Oxygen. The most common include Oxygen Diffusers from Algae, Electrolyzers from Water, Algae Terrariums from Water and Algae, Oxyferns from Carbon Dioxide, and the Rust Deoxidizer from Rust and Salt. The Deodorizer also converts Polluted Oxygen into Oxygen using Sand or Regolith. Natural Oxylite emits Oxygen, and a cluster near the Printing Pod provides early breathing room for the first few cycles. Oxygen can also be harvested from some renewable space POIs in solid or gaseous form.

Oxygen can be useful in more specialized applications as well. When cooled into Liquid Oxygen, it becomes a strong rocket oxidizer for Petroleum Engines and Hydrogen Engines. It is not the best medium for rapid heat transfer, but it is practical for slow heat exchange loops because it can safely mix with surrounding Oxygen if the piping is opened for maintenance, making it easier to work with than many other gases. In those cases, Radiant piping at the heat source and sink is the usual setup.

• Oxygen is often preferred for base infrastructure because it is abundant and easy to route.
• Using Oxygen in a circuit is convenient during maintenance since any leaked gas simply blends with surrounding Oxygen.
• Liquid Oxygen is the relevant end-game form when high-performance rocket oxidizer storage is needed.
• The main downside is that Oxygen production must keep pace with Duplicant demand, especially as the colony grows.