If more than one mixture is necessary for the ascent, redundant breathing gas is typically split between two or more cylinders carried by the diver, and in penetration diving where the diver is constrained to use the same route for exit as for entry, cylinders may be staged, which is a term meaning stowed along the route of the guideline, to be retrieved on the return.

Bailout to open circuit is commonly recommended while dealing with rebreather faults where the composition of the loop gas is uncertain.

[5] A well-known example of this class of bailout bottle is the "Spare Air" set, which can supply a few breaths to allow the diver to ascend at a safe rate, but not enough to do a decompression stop.

[6] "Spare Air" bailout bottles, introduced in the 1980s, are very small cylinders with integral scuba regulators.

[2][8] Surface-supplied divers usually carry the bailout set on a back-mount harness, as this leaves the arms unencumbered for work.

[2] This may be done through an off-board supply connected to the BOV or through a regular fully independent bailout set carried for the purpose.

In closed bell diving an unusually high oxygen partial pressure of 2.8 bar as used in therapeutic decompression was recommended by Association of Offshore Diving Contractors (AODC) and endorsed by the Diving Medical Advisory Council (DMAC) in 1981, on the assumption that if the diver does not make it back into the bell on the bailout gas, or loses consciousness to acute oxygen toxicity, the chances of successful resuscitation will be better than in the case of hypoxia.

[12] This strategy only holds when bailout is at constant pressure, the diver's airway is secured by a helmet, and there is a bellman to assist, as the risk of losing consciousness is relatively high.

The Diving Medical Advisory Council has more recently (2016) made a more conservative recommendation of an oxygen partial pressure for open circuit bailout for saturation divers of between 1.4 and 0.4 bar.