Quick answer: Decompression vs recompression chambers are both specialized hyperbaric pressure vessels, but they serve opposite functions in the diving and medical worlds. A decompression chamber lowers pressure slowly after a dive, so nitrogen can leave the body safely. A recompression chamber, by contrast, raises pressure again to treat an injured diver, often for the bends or a gas embolism. Then it lowers pressure slowly while the diver breathes oxygen. In real life, though, one dual-lock hard-shell chamber often does both.
Decompression vs Recompression Chambers at a Glance
Here’s the short version first.
Decompression chamber
Recompression chamber
Main job
Safe return to surface pressure
Treat a pressure injury
Pressure
Goes down slowly
Goes up first, then down
Who’s inside
A healthy diver
An injured diver or patient
Where
Dive boats, platforms, dive sites
Hospitals, Navy units, dive and tunnel sites
Gas
Air or oxygen, per the dive table
Mostly oxygen, per a treatment table
Who runs it
Dive supervisor and operator
Trained staff, led by a doctor
Still, the line between them is thin. In fact, US rules for commercial diving talk about “a decompression chamber capable of recompressing the diver.” That one phrase shows how much the two jobs overlap.
What Is a Decompression Chamber?
A decompression chamber lets a diver finish decompressing on the surface instead of in the water. When you dive deep or long, your body soaks up extra nitrogen. If the diver comes up too fast, that gas can form bubbles. So the chamber lowers pressure on a set schedule, step by step.
Dive teams use decompression chambers in three main ways, and each also links to recompression.
Surface decompression
First, the diver skips some stops in the water and climbs out. Then they get into a chamber, which the operator quickly brings back to depth pressure. So the rest of the decompression happens there, in a dry and warm space, often on oxygen. Time matters a lot. For that reason, OSHA wants the chamber within 5 minutes of the dive site for many commercial dives.
Deck decompression chambers
A deck decompression chamber, or DDC, is simply a chamber fixed to a ship or platform. It’s where decompression vs recompression chambers overlap most. It handles surface decompression. It also gives the dive team a way to recompress a diver on the spot if something goes wrong.
Saturation diving
In saturation diving, divers live under pressure for days or weeks. Meanwhile, they stay in a chamber complex on the vessel. A closed bell then takes them down to work and back. They also move between the bell and the living chambers under pressure. Finally, at the end of the job, the whole team decompresses together, and that can take several days.
What Is a Recompression Chamber?
A recompression chamber works the other way, because it treats injuries caused by pressure changes. First, it raises the pressure again. Then it lowers it slowly while the patient breathes oxygen.
Two problems drive most of this work, so let’s name them:
- Decompression sickness (DCS): Also called “the bends.” It happens when nitrogen forms bubbles in the blood or tissue.
- Arterial gas embolism (AGE): In this case, gas gets into the arteries, often after a fast ascent hurts the lungs.
Both are on the FDA’s list of cleared uses for hyperbaric oxygen therapy, and the UHMS lists them too. So when people ask about a hyperbaric chamber for decompression sickness, they almost always mean a recompression chamber with trained staff.
One warning, though. If you think someone has DCS, don’t just drive to the closest chamber. Divers Alert Network (DAN) says to call emergency services first. Then call the DAN Emergency Hotline at +1-919-684-9111. Many chambers can’t take diving cases, so a doctor should choose where the diver goes.
How Do Decompression and Recompression Chambers Work?
Both chambers control pressure. But each one leans on a different gas law.
Decompression follows Henry’s law. Under pressure, more nitrogen also dissolves in the body. So pressure has to drop slowly, which gives that nitrogen time to leave through the lungs. Breathing oxygen helps, because each breath then carries less nitrogen in.
Recompression also uses Boyle’s law. When pressure goes up, a gas bubble gets smaller. Here’s how much:
Pressure | Depth | Bubble volume | Bubble width |
1.0 ATA (surface) | 0 FSW | 100% | 100% |
2.8 ATA | 60 FSW | About 36% | About 71% |
6.0 ATA | 165 FSW | About 17% | About 55% |
So pressure shrinks the bubble first. Then oxygen helps clear out the nitrogen inside it. For example, US Navy Treatment Table 6 is the most common table for DCS. It starts at 60 feet of seawater, or about 2.8 ATA. Then, without extensions, it lasts around 4 hours and 45 minutes. If you’d like the unit math, our guide to hyperbaric chamber pressure explains ATA, PSI, and FSW.
In decompression and recompression chambers alike, operators watch the pressure, the oxygen level, and the people inside. They also stay in voice contact the whole time.
Is a Hyperbaric Chamber the Same as a Decompression Chamber?
Need a chamber for diving or treatment work?
Your dive depths and site decide the pressure rating, lock count, and breathing setup. So tell us what you need, and our engineers will help you plan a chamber that meets the rules from day one
Types of Decompression and Recompression Chambers
When you compare decompression vs. recompression chambers, split them two ways. First, look at how the chamber is built. Then look at where it’s used.
How it’s built:
- Monoplace: One person, so no attendant can sit inside.
- Multiplace: Two or more people, so a nurse or tender can sit inside.
- Single-lock: One room, so no one can enter while it’s under pressure.
- Dual-lock: A main room plus an entry lock, so staff can come and go without bringing the patient up.
- Triple-lock: One more room, which helps large sites run more than one treatment.
Where it’s used:
- Deck decompression chambers on dive boats and platforms, since crews work far from shore.
- Transportable recompression chambers for remote or military dive sites, when no hospital is near.
- Medical recompression chambers in hospitals, which also treat other cleared conditions.
- Tunnel medical locks for workers in compressed-air tunnels, along with man locks for daily decompression.
That last group gets less attention. Yet tunnel workers face the same decompression risks as divers. For example, our tunneling chambers include dual-lock man locks rated to 10 bar. They also include a medical air lock built into an ISO container and rated to 5 bar, plus a saturation system rated to 18 bar.
What to Look For in a Decompression Chamber for Divers
For commercial diving in the US, start with OSHA, because its rules set the floor. Its rules in 29 CFR 1910.423 and 1910.430 call for:
- Enough pressure to reach at least 165 FSW (6 ATA) for air dives deeper than 100 feet, mixed-gas dives, and dives past no-stop limits.
- Two locks and room for more than one person.
- A spot within 5 minutes of the dive site, so surface decompression stays on time.
- A pressure gauge for each room that people sit in, too.
- A built-in breathing system (BIBS) with at least one mask per person, since treatment uses oxygen.
- Two-way voice contact, as well as a viewport and lights inside.
- A way to keep oxygen in the chamber air below 25%, because fire risk rises with oxygen.
- Mufflers and suction guards, plus a build that meets the ASME Code.
Beyond the legal basics, however, a few design choices change daily use. For example, the inside width decides whether people can stand up, or whether a patient fits on a stretcher. Door shape matters too. Square doors work better for wheelchairs and gurneys than round ones. Also look at seat count, cooling, noise, and the medical air supply.
Safety, Standards and Recertification
Whether it handles decompression or recompression, every chamber we build follows ASME Section VIII, Division 1, for the vessel. It also follows ASME PVHO-1, the safety standard for chambers that hold people. Our clinical chambers meet NFPA 99, Chapter 14, so each multiplace chamber we build has fire suppression. Then, after a chamber goes into service, ASME PVHO-2 covers its inspections.
Decompression and recompression chambers at dive sites take a beating. After all, salt, shaking, and travel all wear them down. So regular checks, new seals and windows, and recertification matter even more there. We also service chambers from other makers, not just our own. As a result, older or “orphan” diving chambers can often go back into service after testing.
Dive gear needs testing as well, so our breathing simulators test breathing equipment for diving, firefighting and mine rescue at up to 1,000 psi.
Which Chamber Do You Need?
When picking between decompression vs recompression chambers, start with the job, not the name:
- Commercial or offshore diving: You need a two-lock, multi-person decompression chamber that can also recompress to 6 ATA.
- Surface decompression: Then you need a chamber close enough to meet the 5-minute rule, with BIBS for oxygen.
- Diving medicine or emergencies: Instead, you need a medical recompression chamber, a doctor in charge, and room for a tender.
- Tunnel work under compressed air: In that case, you need man locks for decompression and a medical lock for treatment.
- Research: Finally, you need a chamber built around your test plan.
Where PCCI Hyperbaric Systems Fits
We design, build, install, and maintain hard-shell chambers, and that’s all we build. So our lineup is focused. It covers decompression and recompression chambers, including multiplace systems with one to three locks. It also covers tunnel man locks, medical locks, and research chambers. Also, our division head, Ramesh Dixit, PE, sits on the ASME PVHO committee, including its diving subcommittee. He also serves on NFPA and UHMS safety committees.
Frequently Asked Questions
Is a decompression chamber the same as a recompression chamber?
Often, it’s the same chamber. A decompression chamber brings a diver back to surface pressure slowly, while a recompression chamber raises pressure first to treat an injury. In fact, many dual-lock, multiplace hard-shell chambers do both jobs. That’s why OSHA describes “a decompression chamber capable of recompressing the diver.”
Can a hyperbaric chamber treat decompression sickness?
Yes, as long as it can reach the right pressure and trained staff run it. Decompression sickness and arterial gas embolism are both FDA-cleared uses for hyperbaric oxygen therapy, and the UHMS lists them too. But not every center takes diving cases, so a doctor or DAN should guide the referral.
How long do divers stay in a decompression chamber?
It depends on the dive or the treatment, since decompression and recompression chamber schedules differ. Surface decompression times also follow the dive table. US Navy Treatment Table 6 for the bends takes about 4 hours and 45 minutes. After saturation diving, though, decompression can take several days inside the chamber system.
What is a deck decompression chamber?
A deck decompression chamber, or DDC, is a chamber fixed to a dive boat or offshore platform. Divers then use it for surface decompression after a dive. Since it can usually recompress a diver as well, it also acts as the team’s emergency treatment chamber at sea.
Why do recompression chambers need two locks?
A second lock lets a tender, a doctor, or supplies get in while the patient stays under pressure. Without it, though, staff would have to bring the patient back up just to enter, and that could make symptoms worse. That’s why OSHA requires dual-lock, multiplace chambers for many commercial dives.
