Air Envelopes and Atmospheres

While in wildspace, all creatures and objects with weight retain an envelope of air around them depending on their size which lasts until it is depleted. This envelope roughly takes the shape of a ovoid bubble around the creature or object, with its boundary the same distance away from the surface of the creature or object as that creature or object is thick in that direction. Generally, a breathing creature will cycle through their personal envelope of air over the course of 1 minute. Since this is very little time to do anything of consequence, most creatures choosing to enter wildspace do so aboard a spelljammer.

The Air Envelope around a spelljammer is the limiting factor for the ship's Crew Rating. A ship with a full all-breathing crew will cycle through the ship's air envelope entirely over the course of 120 days. A ship with a crew numbering fewer than the ship's Crew Rating will deplete their air supply more slowly, while a ship with more crewmembers than their Crew Rating will deplete their breathable air more quickly; simply multiply the standard 120 days by the ratio of the ship's Crew Rating to the ship's total crew. Mechanically, this ship's air supply will transition between the following conditions:

Fresh Air. This is the highest quality of air and is completely breathable. Under nominal conditions, a ship's fresh air supply lasts for 40 days.

Stale Air. At the start of the 41st day of the crew breathing Fresh Air the air aboard the ship will become stale. A creature breathing stale air cannot remove any points of exhaustion. Under normal circumstances a ship's stale air supply lasts for 40 days.

Foul Air. At the start of the 81st day (or the 41st day of having Stale Air) the air aboard the ship will become foul. A creature breathing foul air still cannot remove any points of exhaustion and gains the poisoned condition. Under normal conditions a ship's foul air supply lasts for 40 days.

Toxic Air. At the start of the 121st day (or 41st day of having Foul Air), the air will become toxic to the crew. A creature that tries to breathe toxic air will begin to suffocate.

Overlapping Envelopes

When two bodies overlap their air envelopes, the envelopes merge and become the same quality as the air that was surrounding the body whose envelope had the greater volume. For example, a smaller ship with stale air overlapping envelopes with a larger ship that has foul air will have it's air supply depleted to foul upon the envelopes merging and once the two ships separate both ships will redevelop their own distinct envelopes, now with the same foul quality air. The only bodies whose air envelopes don't deplete are those of planets, who, without extensive intervention, constantly refresh their air supply to their characteristic quality -- these air envelopes are colloquially called "atmospheres".