Density - caraminden/anathema-roguelike GitHub Wiki

When a Gas is created it starts with a Density value between 10% and 100%, every Segment the Gas will propagate to adjacent Locations, decreasing the Density of that Location and increasing it in the adjacent Locations. Once Density drops below 10% the Gas is considered completely dissipated and will no longer spread or have an effect on the characters at that Location.