Rust

Rust is a general decay system that serves to amplify the effects of other threats on the station by compromising the integrity of the environment. Unlike other forms of decay, which work directly to injure players, rust is not inherently harmful. Since it's a lot more slow-moving, rust can spread and begin to destroy the station long before people notice it and begin to fix it.

Additionally, rust is a strong thematic element that is instantly understandable. Rusty walls, tiles, and machines create strong mental images of decay and ruin. Their compromised functionality is easily understandable, as it mirrors the real-world interaction of struggling to manipulate or protect something which has been attacked by rust.

Buildup

Rust buildup is characterized by 3 distinct stages that progress both visually and in function:

• Stage 1: The object begins to show visible rusting. No other effects are present, as this is simply a warning that there is an issue that has to be taken care of.
• Stage 2: The object becomes worse at its function. The rust visuals are more prevalent and the object no longer functions as well as it should. Walls become significantly weaker, doors get stuck and must be pried, and atmos floor devices lose throughput. This creates another warning that, while reversible, begins to compromise the functionality of structures.
• Stage 3: The object has completely rusted off. At this point, the object is completely unable to function and can trivially be destroyed. Doors become little more than walls, walls become functionally grilles, and machines become little more than set dressing. Reversing rust at this point is not possible and the object must be entirely replaced.

The goal with the progression of buildup is to create a distinct warning and consequence. As rust begins to form, the crew are given a good amount of time to respond to its source, removing the decay vector and working to repair damage done. This is pretty easy to do, and can be accomplished either with a basic welder or through some specialized rust-removal tool. If they manage to contain the source, the department will be left mildly compromised yet still functional, with the ability to repair it to restore it to its original state.

Only by completely ignoring the rust and allowing it to grow are the crew left with the worst outcome, where the area will become completely rusted and nonfunctional. Due to the nature of the damage and sources, this will then likely cause it to spread to other areas, causing further decay across the station.

Water Vapor

Rust is spread through the presence of water vapor on station. When a rustable object is adjacent to or covered by water vapor, it has a chance to rust, consuming a small amount of water vapor.

Water vapor is a good source of rust and decay since it interfaces with key simulation systems while also having inherent beneficial properties. Namely, it's the logical byproduct of a variety of reactions and machines, giving it varied sources which can logically accumulate in different parts of the map. On top of that, the natural flow of gas works in tandem with the rusting of walls, allowing the water vapor to spread further into the station.