The recompression chamber is the equipment that turns a dysbaric accident into a treatable incident. Having one is not enough: it has to be operational, pressurisable within minutes, with enough gas, with qualified personnel to run it, and close enough to the dive site to be used in time. All of that is set by the applicable regulations and the project's emergency plan.
On a professional dive site there is a lot of important equipment and one piece that you hope never to have to use. The recompression chamber is that piece. It sits there, takes up deck space, needs maintenance, uses up gas in testing and produces absolutely nothing, until the day it is the only thing that matters.
Its presence is also one of the clearest markers for telling a serious operation from one that isn't.
What it is and what it does
A recompression chamber is a steel enclosure capable of holding pressure above atmospheric inside it, with its own gas supply system, atmosphere control, communication with the outside, and devices for the occupants to breathe specific mixtures.
Its therapeutic use rests on two effects. Raising the pressure shrinks the gas bubbles that have formed in the body and redissolves them, which relieves the immediate mechanical problem. And breathing oxygen under pressure speeds up the elimination of inert gas and improves oxygenation of the affected tissues.
Treatment is not improvised: established tables are applied, setting what pressure the patient is taken to, how long they stay there, what they breathe at each stage and at what rate they are brought back to atmospheric pressure. Choosing the table and following it are medical decisions.
All of this is the outcome of a condition explained in more detail in the article on decompression sickness.
When you have to have one at the dive site
Here it pays to be precise and cautious at the same time: the specific requirements vary between jurisdictions and between certification schemes, and any figure given without saying which regulation it comes from is useless or dangerous information.
What can be said in general is the pattern. Professional schemes require a chamber on site, immediately available, for bell diving and for any dive involving planned decompression. For no-decompression diving at moderate depths, the requirement is set in terms of availability and maximum time to reach a suitable facility.
The underlying criterion is always the same: time. A serious dysbaric accident is treated better the sooner it is treated, and a chamber that takes hours to reach is a fundamentally different thing from one twenty steps away. That is why the project's emergency plan has to state, in writing and with names, where the chamber is, how to get there, how long it takes and who operates it.
The applicable reference is the regulations of the country where the diving takes place and the scheme set by the contract. Checking that is part of what any diver should verify before accepting a campaign, just as they check their medical or their insurance.
What a deck chamber looks like
The usual set-up in professional operations is the twin-lock chamber: two compartments connected by a lock with independent doors. The reason is practical. With a single compartment, anyone entering or leaving forces everyone to depressurise; with two, an attendant can enter mid-treatment and medication, water or equipment can be passed through without interrupting anything.
The main compartment houses the patient and their attendant, with bunks or seats, lighting, two-way communication, and masks or hoods for breathing oxygen. The lock is smaller and serves as the passage between them.
Around the chamber there is as much equipment as inside it, if not more: the control panel with its gauges and valves, the gas supply with its cylinders and reserve, the internal atmosphere analysis system, communications and, if the campaign requires it, temperature and humidity control. None of this is optional, and gas is managed with the same discipline as at the gas panel on the dive.
Who runs it
Operating a chamber is not just opening a valve. It requires personnel specifically trained and accredited for it, able to follow a table, control pressurisation and decompression rates, manage the internal atmosphere and respond to whatever happens inside.
On a diving operation, that responsibility sits within the chain of command: the diving supervisor directs the response, the chamber operator carries it out, and the treatment itself is conducted with the assistance of the designated doctor or hyperbaric medicine specialist, who may be present or reachable by communication as the plan provides.
Many operations also have a team member trained as a diver medic, able to give the first response and accompany the patient inside the chamber. It is one of the most useful additional qualifications a diver can hold, and one of the ones that carries the most weight on a CV.
Ready to use, not just present
Having a chamber and having an operational chamber are different things, and the difference is checked every day.
Before each day's work it is checked that the chamber pressurises, that there is enough gas for the worst-case scenario allowed for, that communications work, that the masks are in place, that access is clear and that the designated personnel are on board. All of it is logged. A daily record of these checks is, in practice, the best sign that an operation is being run properly.
The failures seen in practice are almost never in the chamber itself: they are in the surroundings around it. Gas that's cutting it too fine, a compressor that hasn't been started in weeks, a passage blocked with equipment that a stretcher can't get through, or a team that has never rehearsed moving an unconscious diver from the water to inside the chamber. That rehearsal is exactly what drills practise, which is why they are run.
Portable, fixed and transfer chambers
Not all chambers are the same, and they don't all serve the same purpose. The deck chambers used on surface-supplied diving operations are relatively compact units, meant to be set up at the work site and moved with the campaign. Those on a dive support vessel (DSV) are part of the vessel's fixed installation and are much larger, because they have to house the saturation team for weeks at a time.
There are also chambers designed to transfer a patient who is already under pressure, allowing them to be moved to a larger facility without being brought back to atmospheric pressure on the way. They are the hyperbaric equivalent of an ambulance, and their compatibility with the receiving chamber is not a minor detail: mating two systems that don't fit together is a problem that turns up at the worst possible moment.
That same mating principle governs transfer under pressure in saturation, where moving people between compartments without losing pressure is a routine, tightly regulated operation.
Its other role
It's worth remembering that the chamber is not only emergency equipment. In saturation diving the chamber system is where the team lives for the whole campaign, and on bell diving it is used for planned decompression at the end of each working day.
In other words, for a good part of the trade, going into a chamber is not the exception but the routine. And that means familiarity with it — how it sounds, how it smells, how you communicate from inside — is part of the basic training for anyone who wants to work in offshore professional diving.
This article describes how the resource is organised, not how a patient is treated. Any clinical decision is a matter for competent medical personnel.
Frequently asked questions
What is a recompression chamber?
A pressurisable enclosure where a person is put under pressure above atmospheric to treat decompression sickness or a gas embolism, following a treatment table and normally breathing oxygen under pressure.
When is it mandatory at the dive site?
It depends on the applicable regulations and the type of dive. Professional schemes require a chamber on site for bell diving and for dives with decompression, and set availability and proximity conditions for the rest. The valid reference is always the country's legal framework and the project's scheme.
Who can operate a chamber?
Personnel specifically trained and accredited as chamber operators, under the responsibility of the diving supervisor and with the assistance of the project's doctor or hyperbaric medicine specialist for the treatment itself.
What is a twin-lock chamber?
A chamber with two compartments separated by a lock, so that someone can enter or leave without depressurising the patient. It's what allows an attendant to enter mid-treatment or medication and equipment to be passed through.
Is the chamber only used to treat accidents?
No. In saturation diving the chamber is also where the team lives for the whole campaign, and on bell diving it is also used for planned decompression. Therapeutic use is only one of its functions.
What fails most often with a chamber?
Rarely the chamber itself. What fails is the surroundings: insufficient gas, a compressor that won't start, communications that don't work, personnel who haven't practised the procedure, or access blocked by equipment on deck. That's why the checks are done daily and logged.
Published 1 September 2026 · By Arthur More, professional saturation diver
Photo: stevesimo · CC BY via Openverse
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