From Unofficial Stationeers Wiki
Atmospherics is one of the main simulated systems in Stationeers. The game world consists of many individual units of atmosphere that interact with each other as well as structures and items that are in contact or intersecting with them.
Each unit of atmosphere simulates a number of properties, these properties generally change over time as the atmosphere interacts with the surroundings.
Each unit of atmosphere contains its' own composition of gasses and liquids represented in quantity by mol. Common gasses are Oxygen, Volatiles, Nitrogen, Carbon Dioxide and Pollutant. Water is the only liquid currently simulated.
Stationeers attempts to simulate thermodynamics by having atmospheres contain heat energy. The effective temperature of one atmosphere depends on the heat energy relative to the amount of gasses in the atmosphere. This means that a very small atmosphere can reach very high temperatures with a small amount of added heat.
Pressure is a product of the contents of the atmosphere adjusting by temperature/heat.
Large Grid Atmosphere
The most common type of atmosphere is the large grid atmosphere. In the main game world, each large grid unit (the size of a Frame) contains one unit of atmosphere. The atmosphere in one large grid will exchange contents and heat with neighbouring atmospheres in order to equalize their content. An atmosphere in a vacuum will eventually spread out and dissipate in within a few large grid atmospheres of distance.
Each individual pipe network is simulated with one atmosphere. If you break up a pipe network with a device such as a pump or valve, you effectively control the interaction of gasses between the two atmospheres.
Individual structures that contain atmospheres (static tanks, etc) will interact either with a pipe network or directly with the surrounding atmosphere, it depends on the configuration.
Some items in the game contain their own units of atmosphere, such as Canisters, Suits and even the players' Lungs. Items with atmospheres, just like other atmospheres, can be heated by direct sunlight, leading to canisters bursting by pressure, or fuel autoigniting(exploding) at high pressure/temperature.