What is saturation diving?

What is meant by saturation and decompression in diving?

Rather than get into the complexities of diving science, I like to use a simple analogy to explain saturation.

Imagine you have a bottle of carbonated drink. The drink has gas dissolved into it to make it fizzy. You shake the bottle and open it. A geyser of foam erupts, causing a mess. Not ideal.

You take a second bottle and shake it, only this time you’re more careful. You let the drink sit for a while before slowly twisting the cap off the drink. Bubbles appear and dissipate gently.

When you dive underwater you are at a greater pressure than on the surface. Like the carbonated drink, you start to absorb that higher pressure gas into your tissues, blood – your whole body.

Saturation is where you stay at any given depth for long enough for your body to have absorbed as much gas as is possible, because the gas absorbed into tissues is equal to the pressure around you.

When you return to the surface from depth, all that dissolved gas wants to make its way out of your body in a process known as decompression. Like in the fizzy drink analogy, if this is too rapid and uncontrolled, you’ll suffer from decompression sickness, which you might have heard called “the bends.”

Once you reach saturation, the time for decompression is the same. It doesn’t matter whether you spend one day at depth, two days, or twenty. So, if you have an underwater task that will take 12 hours, for example, it’s safer and more efficient to stay saturated for the entire task and decompress once, rather than cycling through multiple dives and decompressions.

What is decompression sickness or “the bends”?

Decompression sickness happens when dissolved gases form bubbles in the body due to rapid pressure reduction, usually from surfacing too quickly after a dive. It can cause joint pain, dizziness, and serious complications in severe cases.

The way we mitigate the risks of decompression sickness is by controlling our exposure to pressure and our ascent. We might limit bottom time, ascend slowly, and make a series of stops on the way to the surface, almost like climbing a staircase.

What this means is our time underwater is very limited, and the deeper you go the less productive time you have.

The solution to this a saturation diving system such as a closed diving bell and pressurised living chamber, or an ambient pressure subsea habitat, such as Vanguard. Using these systems, divers can live at depth and decompress once at the end of their shift, which greatly reduces the risk of decompression sickness and is a gamechanger for productivity.

^{A diagram showing productive time and decompression requirements at different depths.}

How does saturation diving from a closed bell work?

Closed bell saturation diving allows you to live under pressure for days or weeks at a time. Instead of making multiple long ascents and descents - which would increase the risk of decompression sickness - divers are transported to and from the worksite in a sealed, pressurised chamber known as a diving bell.

Once you are lowered to the intended depth, you can exit the bell and dive. An umbilical provides breathing gas, communications, and heating (hot water).

In a three-person bell set up, you’ll have diver one and diver two who will be in the water completing their tasks. A third person, known as the bellman, will stay inside the bell monitoring the life support systems and communicating with the divers and the surface.

At the end of a shift the divers re-enter and seal the bell before being winched back to the surface still under pressure. The bell is then reconnected to the chamber that sits on the surface (on either a vessel or platform). This chamber is kept at the same pressure you dive at, and it means you can eat, sleep, and rest between shifts without needing to undergo decompression.

Because you’re under constant pressure, you can decompress once at the very end of the job, making deep-sea operations safer and more efficient.

How deep do saturation divers go?

Commercial saturation diving operations typically take place between 100 and 300 meters. This is the range where oil, gas, and subsea construction work is often carried out.

In theory, it’s possible to dive to greater depths than this. But the risk, cost, and complexity of going significantly beyond 300–350 meters usually outweighs the benefits.

Saturation diving makes it possible to work at greater depths than scuba allows. To make these greater depths possible, saturation divers will breathe carefully calculated and controlled gas mixtures rather than normal air.

At great depth, nitrogen becomes narcotic (producing a dangerous drowsy effect) and oxygen can become toxic at high pressures. What’s more, as pressure increases, air becomes heavier, making the physical effort of breathing increasingly strenuous.

To avoid these dangers, the nitrogen is replaced with helium, creating what’s called heliox (helium–oxygen). Helium is lighter than air, non-narcotic, and allows divers to function safely under extreme pressure.

What are some common myths and misunderstandings about saturation diving?

Myth: Deep-sea divers always live on the seafloor for weeks at a time

This depends on the method of saturation diving. For commercial diving from a closed bell, the pressurised living chamber sits on the water’s surface, either on a purpose-built vessel or platform.

When diving from a subsea habitat, the living chamber sits on the ocean floor and divers will live underwater for the duration of their mission.

Myth: Divers can just surface and go home when the job is done

Unlike recreational scuba, saturation divers can’t simply ascend at the end of the job. Because their bodies are saturated with gases, decompression can take days to over a week depending on the depth. This must take place in a carefully controlled process while inside the living chamber.

Myth: Saturation diving is just scuba, but deeper.

The systems are very different for scuba and saturation diving. Saturation diving relies on specialised gas mixtures, complex life-support systems, and closed environments that keep divers under pressure around the clock. It’s a highly technical operation managed by a large support team on the surface.

Myth: Becoming a saturation diver is just about diving skills.

Physical diving skills are only part of the picture. Training also covers mental resilience, handling confinement, and being able to perform complex, high-pressure tasks for weeks at a time inside a controlled, pressurised environment.

How do you train to become a saturation diver?

Most saturation diving training takes place in dedicated commercial diving schools. These are equipped with complete closed bell training systems, which provide a high-fidelity, controlled environment for learning.

It’s not just about learning the diving skills, but the technical skills surrounding complex life-support systems, gas management, closed bell operations, and emergency procedures. It also involves learning to live in pressurised chambers for weeks and working long hours under high pressure.

Saturation systems are complex and expensive to build and maintain. They also take a great deal of expertise to operate. For these reasons, there is a short supply globally of high-quality facilities for training – something that DEEP is helping to alleviate by bringing a training facility to the market in 2026.

^{A render of DEEP’s saturation training facility expected in 2026.}

Does DEEP offer saturation diving training?

Yes! Work is underway at DEEP to construct a state-of-the-art saturation diving facility at its Campus facility in the Southwest of the UK. Once operational, it will be a world-class modern saturation system offering training with a globally recognised qualification.

The system, three years in the making, has been fully designed and specified to DEEP’s training requirements, with a three-person diving bell, nine-person hyperbaric rescue craft, and split living and sleeping chambers for comfort.

How does saturation diving fit into DEEP’s mission?

The concept of saturation is central to the idea of humans living and working underwater.

I completed my saturation training in Fort William on the west coast of Scotland, not far from Ben Nevis. The reason for doing so was in preparation for a media job where we would use a pressurised chamber to live in, and the closed bell to go to a site to film.

This saturation capability was transformational. Instead of a brief 20 or 30 minutes on the bottom because of decompression requirements, we could spend six hours on the bottom, stay pressurised, sleep, eat and wash – then do another six hours and decompress once at the end.

To give you an idea of the difference in productivity, a project that would take six weeks to accomplish in 70 meters of water with traditional surface diving methods, would take about four days with a closed bell system or subsea habitat.

Bringing a comprehensive saturation system to DEEP Campus is a critical step to train both commercial divers and individuals who will spend time in one of our subsea habitats.