Bailout

An independent open-circuit gas supply carried by rebreather divers, sufficient to abort the dive and complete decompression if the unit fails.

Bailout is the independent open-circuit gas a rebreather diver carries so that a failure of the unit never becomes a failure of the dive plan. If the rebreather floods, a sensor set becomes untrustworthy, or the scrubber is suspect, the diver bails out: switches to a regulator fed from separate cylinders and completes the ascent and any required decompression entirely on open circuit.

The core planning rule is that bailout must be sufficient to get you from the worst point of the dive to the surface, including all decompression stops, at a realistically elevated breathing rate, since a diver bailing out is stressed and working. Deep dives may require multiple bailout cylinders staged as side-slung stage bottles, often a deep mix plus one or more deco gases, each marked with its maximum operating depth. Teams sometimes plan shared team bailout on expedition dives, though many divers prefer full independent redundancy.

The term also appears loosely in open-circuit diving for any redundant escape gas, such as a pony bottle carried on deep recreational dives. The planning mindset transfers directly: a reserve only counts if it is truly independent of the primary supply, big enough for a realistic worst case, and reachable and deployable with cold hands and elevated breathing, not just on paper.