Air
From Starbounder - Starbound Wiki
Air is a limited resource that the player will slowly lose when they are underwater or in environments with no oxygen. Available air is measured through a UI element that appears when the player is losing breath. The breath meter decreases at a rate of 1 bar every 5 seconds when air is unavailable. Once it is empty the player will lose health and eventually die.
The air meter will refill itself when the player returns to a breathable environment at a rate of 2 bars per second.
Breathing Enviro Protection Pack
The Breathing EPP supplies endless air to the player. This is vital for moon travel or ocean exploration, and can be useful when stuck under a solid tile such as Silt.