At the end of a campaign, the team spends several days rising very slowly inside the chamber to atmospheric pressure. It's a slow process, measured and medically monitored, in which the body clears the dissolved helium. It can't be shortened: the pace is set by physiology, not the client's schedule.
After weeks living under pressure, working shifts and going down in the bell, the last working day arrives. And then comes the part that gets the least coverage: final decompression, several days shut in doing nothing while the gauge needle drops at a pace that feels maddening.
Why it's needed, and why only once
During the campaign, the diver's tissues have saturated with helium at the storage pressure. Saturated means exactly that: they've absorbed all the gas they can hold at that pressure, and beyond that point extra time no longer changes the amount dissolved. That's the property that makes the whole system possible, and it's explained in detail in why a saturation diver decompresses only once.
The consequence is that decompression doesn't depend on how many days have passed — ten or twenty-eight makes no difference — but on the storage depth. Bringing the body back to atmospheric pressure means clearing all that gas through breathing without it forming bubbles along the way. And that takes time.
How fast the ascent goes
The actual tables are each operator's own property and vary by depth, gas mix and applicable regulation, so any exact figure given as universal is false. The order of magnitude, though, is consistent across the industry: ascent runs a few metres an hour, with long hold periods, and the total duration is roughly a day for every twenty-five to thirty metres of storage depth.
In practice that means a saturation at a hundred metres decompresses in about four days, and a deeper campaign can take a week. With two particularities:
- The ascent stops at night. Pressure is held steady during the sleep period and resumed in the morning, because monitoring symptoms during rest is worse.
- The last few metres are the slowest. The relative pressure gradient grows the closer you get to the surface, so the final ten metres demand more care than the first fifty.
What happens during those days
Nothing, and that's the hard part. The work is finished, the team is still shut in the same space as always, and there are no more shifts to structure the day. People read, watch films, sleep a lot, talk to the surface. The chamber atmosphere gradually enriches with nitrogen as the pressure drops, so voices slowly recover their normal tone and the environment becomes more bearable thermally.
Many divers describe those days as the worst part of the campaign, worse than the work. It's a stretch where the body wants out and the clock won't cooperate. Anyone wanting a feel for the environment can read what life is like inside the saturation chamber.
Medical monitoring
Throughout decompression, the life support technician keeps the record of atmospheric parameters and the supervisor checks on the team's condition at fixed intervals. Symptoms are actively asked about: joint pain, tingling, skin changes, dizziness, altered sensation. A hyperbaric doctor is available, either on site or reachable, and the chamber itself is the treatment facility if needed.
The advantage of decompressing inside the system is obvious: if a sign of decompression sickness, the response is immediate. All it takes is recompressing — that is, undoing part of the ascent — stabilising, and resuming afterwards with a more conservative profile. There's no transfer, no wait, no ambulance. That's one of the reasons why, statistically, well-run saturation decompression is remarkably safe.
What it feels like
The most common thing isn't pain, but exhaustion. A deep fatigue that many put down to the process itself, which can last several days after coming out. Also common:
- Mild, diffuse joint discomfort, which usually settles on its own.
- Transient skin itching.
- A persistent feeling of cold during the upper part of the decompression.
- Irregular sleep and a feeling of grogginess.
- Occasionally, ear discomfort if there's congestion.
Any of these symptoms gets reported to the supervisor. The professional culture on this point is clear: keeping quiet about a niggle to avoid delaying the exit is the most costly mistake a diver can make, because what's at stake is potentially permanent spinal cord injury.
After the door opens
Leaving the chamber doesn't close out the process. There are restrictions afterwards that are part of the procedure and that industry guidelines set out explicitly:
- No volar for a minimum period after decompression, because an aircraft cabin means going up even higher.
- Not returning to saturation until a minimum surface interval has passed, related to the length of the previous exposure.
- Permanecer localizable and near a recompression facility during the first few hours.
- Avoiding intense physical exertion for the first few days.
Those restrictions shape the logistics of getting home and explain why offshore diver rotations always include a margin between leaving the chamber and the flight home.
Why it can't be sped up
It's the question that comes up most, usually from the client's side, when the vessel has a closing weather window or a contract running down. The answer is that the rate at which dissolved gas clears is set by the physiology of gas transport in the tissues, and there's no operational lever that changes it. Compressing again can be done in minutes; decompressing can't.
That's why final decompression is planned as a phase of the contract from day one, with its own cost in vessel time, crew time and schedule. It's one of the reasons a saturation job is expensive and gets worked out in pencil before anything is mobilised, as explained in the breakdown of what a diver earns and in the markets where the work happens.
What changes in the body during those days
Decompression isn't just waiting. It's an active process in which dissolved gas moves from the tissues into the blood and from the blood into the alveolar gas, to be expelled with each breath. That transfer doesn't happen at the same rate in every tissue: blood and well-perfused organs clear quickly, while fat, bone and cartilage take much longer. Decompression tables are nothing more than managing the slowest compartment.
That lag explains two things that puzzle newcomers. First, that the ascent rate has to be held even when everyone feels perfectly fine: the slow tissues give no warning. Second, that symptoms of a problem can appear hours after a specific manoeuvre rather than at the time.
Temperature, hydration and rest
Three variables the team controls that directly affect how effectively gas clears. Chamber temperature is kept within a narrow band, because cold reduces peripheral perfusion and slows the transfer exactly where it's needed most. Hydration is explicitly monitored, since dehydration worsens blood rheology. And rest matters because intense exercise during decompression encourages gas nuclei to form.
None of this is exotic: they're the same variables any diver would look after following an ordinary dive, only here they're managed continuously for days and logged shift by shift by the life support team.
Frequently asked questions
How long does saturation decompression take?
It depends on the storage depth, not on how long the campaign lasted. The usual order of magnitude is a day for every twenty-five to thirty metres, so a saturation at a hundred metres runs to around four days.
Why doesn't the duration depend on how many days were spent down there?
Because the tissues saturate with inert gas up to a limit set only by pressure. Once that's reached, staying longer doesn't add any more dissolved gas, so it doesn't lengthen decompression.
Does decompression continue at night too?
No. It's standard to stop the ascent during the sleep period and hold pressure steady, because monitoring symptoms and responding to a problem are both harder while the team is asleep.
What does final decompression feel like?
Mostly fatigue, along with mild joint discomfort, skin itching, a feeling of cold and irregular sleep. Any of these symptoms must be reported to the supervisor, since it could be the first sign of decompression sickness.
What happens if a symptom of decompression sickness appears?
The diver is recompressed inside the system itself, stabilised, and then brought back up on a more conservative profile. The advantage of decompressing in the chamber is that the treatment facility is the same place the patient is already in.
Can you fly right after leaving the chamber?
No. There's a minimum waiting period before flying, because an aircraft's cabin pressure is equivalent to continuing to ascend. That margin is built into the diver's return travel planning.
Published 24 August 2026 · By Arthur More, professional saturation diver
Photo: infomatique · CC BY-SA via Openverse
This article is part of our in-depth guide to commercial diver requirements: the medical, eyesight and age limit — the complete picture, with sources.
This article is part of our in-depth guide to commercial diver requirements: the medical, eyesight and age limit — the complete picture, with sources.
This article is part of our in-depth guide to commercial diver requirements: the medical, eyesight and age limit — the complete picture, with sources.
This article is part of our in-depth guide to commercial diver requirements: the medical, eyesight and age limit — the complete picture, with sources.