Air Tank (5e Equipment)
From D&D Wiki
An air tank is a lightweight, highly pressurized tank containing a breathable mixture of air that can be attached to a sealed or airtight suit of armor or clothing. While the air supply holds out, you are immune to the effects of inhaled chemicals, toxins, or particles. Your air supply is also entirely self-contained, allowing you to breathe without issue in an environment where there is no air at all, or the air is completely unbreathable (an alien atmosphere that completely lacks oxygen, for example). Air tanks use sophisticated rebreather systems to recycle and reuse air, significantly expanding their lifespan
An air tank lasts for 24 hours of use, after which it must be refilled in order to provide further benefit.
Weight: 4 lb.
Variant. The above statistics assume that the air tank is designed for a Medium creature. For every size category a creature possesses above Medium, it breathes four times as much air. The weight of air tanks for larger creatures increases proportionately. For example, an air tank sized for a Large creature would weigh 16 pounds. Meanwhile, small creatures breathe¼ as much air, and tiny creatures breathe 1/16 as much air; decrease the weight of air tanks for such creatures appropriately.