Decompression, Stage & Bailout Cylinders

BY CHRISTINE TAMBURRI

Diving equipment often goes by different names, depending on the training agency or the part of the world where you were trained: What some divers call a dive light, for example, others might call a dive torch These names are synonymous, and the worst that can happen by interchanging them is that it might give away where you were trained (and possibly provoke minor jesting) or lead to minor misunderstandings However, actual harm is very unlikely.

On the other hand, sometimes, terms that seem to be synonyms refer to entirely different devices For instance, a spool and a reel might seem similar but are not: Reels do contain spools, but spools – as such – are functionally different from reels. Hence, the term you use has a direct bearing on its method of operation and application. Interchangeable use may, therefore, not be innocuous and may even result in injuries..

In some cases, a piece of equipment has multiple uses Divers might describe the same object as a decompression cylinder, a stage cylinder, or a bailout cylinder Although the device may be identical, its application and the training required to use it safely may differ vastly.

So, divers need to know the difference between simple synonyms and particular technical use of terms when referring to a piece of diving equipment.

Cylinder Similarities

Technical divers may use decompression cylinders, stage cylinders, and bailout cylinders during complex dives involving a variety of gas mixes and applications Depending on the dive they are planning, these cylinders are typically carried in addition to the primary configuration such as doubles, side mounts, or rebreathers. Special contingency gas planning is necessary when diving with such cylinders to ensure that, in case of a catastrophic failure, all divers can return to the surface safely.

The size of the cylinder may vary with its use Twelve-litre aluminium cylinders are popular, but often cylinders are used that are half that size Ten-litre cylinders may also be used as decompression or bailout applications Because steel cylinders are negatively buoyant, aluminium ones are generally preferred Regardless of the size, however, the rigging is typically similar, with slight variations from diver to diver to meet their individual needs.

Cylinder Differences

Decompression cylinders: As the name suggests, decompression cylinders contain gas that divers use during staged decompression dives, which include stops at various depths for predetermined lengths of time before surfacing to allow for efficient off-gassing Decompression gas typically contains more than 40 percent oxygen A diver may carry more than one decompression mix on longer, deeper dives.

In non-overhead environments, divers typically carry decompression cylinders throughout the dive and breathe from them after reaching a safe depth for the mix’s maximum operating depth (MOD) Divers try to avoid dropping these cylinders when diving in open water so they can ascend at any point during the dive if an emergency arises.

In overhead environments such as caves, most divers leave their decompression cylinders at the beginning of the dive for use when they reach the exit This practice is acceptable because there is typically only one way in and out.

Stage cylinders: Stage cylinders allow divers to increase penetration distance in an overhead environment, such as a cave, wreck, or mine.

Divers breathe from cylinders that they place at predetermined intervals along their path Some divers drop these cylinders based on pressure, while others drop them based on time While making their way out, divers pick up the cylinders and use them Regardless of the divers’ gas management method, all team members must agree on a procedure before commencing the dive.

Note that environmental conditions may affect a chosen procedure, such as carrying a stage cylinder further into high-flow cave systems so that gas is more readily available in case it is needed quickly.

Bailout cylinders: Rebreather divers use bailout cylinders in case a catastrophic loop failure requires a switch to open circuit. Divers must be mindful of the bailout cylinder gas’s MOD, because they must be able to breathe it at the dive’s maximum planned depth.

Unlike stage cylinders, divers carry bailout cylinders throughout the dive to immediately access breathing gas if a rebreather failure occurs. Some dive plans for overhead environments include placing additional bailout cylinders at predetermined distances.

A diver must always have sufficient gas attached to them for the transport time needed to travel safely to their next previously dropped cylinder. The best practice is for each diver to carry enough bailout gas to perform a self-rescue and get back to the surface safely on their own.

Closing Thoughts

Divers need extra training to carry additional breathing gas. Whether decompression, stage, or bailout cylinders, each requires additional training Divers may take further training courses on decompression procedures, wreck penetration, or cave diving to expand their skills and knowledge Even though these cylinders may look the same in size and rigging, each has a unique function within a given dive plan It is important to note that divers may carry more than one type of cylinder on any given dive, such as having both stage and decompression cylinders on an open-circuit cave dive.

Divers are encouraged to abide by their training agency’s recommendations and stay within the scope of their training This helps ensure that every dive is as safe as possible Divers should strive to understand the terminology and use it appropriately Doing so helps decrease confusion, which ultimately increases a team’s safety.

Decompression cylinders, stage cylinders, and bailout cylinders are different pieces of equipment Correctly referring to each type will ensure everyone knows their intended use.