Rebreather

A breathing system that recycles exhaled gas, scrubbing carbon dioxide and adding oxygen, producing few or no bubbles and long dive times.

A rebreather recycles your breath instead of venting it into the water. Exhaled gas passes through a scrubber canister of soda lime that removes carbon dioxide, oxygen is added to replace what your body consumed, and the refreshed gas returns to you through a breathing loop with counterlungs. The result is remarkable efficiency, since a diver metabolizes only a small fraction of the oxygen in each open-circuit breath and wastes the rest as bubbles.

On a closed-circuit rebreather, electronics or a manual diver hold the oxygen partial pressure at a chosen setpoint, commonly around 1.2 to 1.3 bar, which optimizes decompression at every depth. The gains are silence and gas economy, letting divers approach wary wildlife and run long deep dives on little gas. The costs are complexity and unforgiving failure modes: hypoxia, hyperoxia, and hypercapnia can all develop with little warning, so training and disciplined checklists are non-negotiable.

Every rebreather diver carries open-circuit bailout to escape a failed loop. Once a technical niche, rebreathers now appear in recreational forms, but the checklist culture stays the same everywhere.