Air Quality

The air envelope around a body or ship can be fresh, foul, or deadly. Air can change from one quality to another over time.

Fresh air is completely breathable. If a ship carries more creatures than its normal crew complement, they exhaust the supply of fresh air more quickly.

Foul air is stale and partially depleted. It is humid and smells bad. Any creature that breathes foul air becomes poisoned until it breathes fresh air again.

Deadly air is unbreathable. Any creature that tries to breathe deadly air begins to suffocate (see the rules on suffocation in the Player’s Handbook).

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Foul Air can be restored to fresh air using the Fog Cloud spell. However it has no effect on Deadly Air.