Saturation diving is a specialized technique that allows divers to work at significant underwater depths for extended durations. Divers remain at high pressure for days or weeks without daily decompression. This method enhances efficiency and safety for prolonged underwater tasks, such as those in offshore energy, construction, and scientific research.
The Science of Saturation
The human body absorbs inert gases, like nitrogen and helium, when exposed to increased pressure underwater. As a diver descends, the ambient pressure rises, leading to higher partial pressures of the gases in the breathing mixture. These gases then dissolve into the blood and tissues, a process described by Henry’s Law. This principle states that the amount of gas dissolved in a liquid is directly proportional to its partial pressure above the liquid.
Over time, if a diver remains at a constant depth, their body tissues will absorb the maximum amount of inert gas possible for that pressure, reaching a state known as saturation. Once saturated, further exposure at that depth does not increase the amount of dissolved gas, meaning the required decompression time remains constant regardless of how much longer the diver stays. This makes extended deep-water operations feasible by eliminating the need for repeated, lengthy decompressions after each work period.
The Saturation System and Equipment
Saturation diving relies on a sophisticated system of components to maintain a pressurized environment for divers. The core of this system includes living chambers, often called habitats or Deck Decompression Chambers (DDCs), located on a support vessel or offshore platform. These chambers are pressurized to match the ambient pressure at the working depth, providing a dry, controlled living space for divers.
Divers are transported to and from the underwater worksite using a specialized vessel called a diving bell, also known as a Submersible Decompression Chamber (SDC) or Personnel Transfer Capsule (PTC). This bell is a pressure-resistant chamber that locks onto the living chambers, allowing divers to transfer under pressure without exposure to surface conditions. Once at the worksite, the bell maintains the divers’ pressurized environment while they exit to perform tasks. Breathing gas mixtures, typically heliox (helium and oxygen) or trimix (helium, oxygen, and nitrogen), are supplied to both the chambers and the bell, carefully tailored to prevent issues like nitrogen narcosis and oxygen toxicity at depth.
The Saturation Diving Process
Saturation diving begins with divers entering pressurized living chambers, where they are slowly pressurized, or “blown down,” to the target storage depth. This initial compression can take a few hours, depending on the depth, allowing their bodies to gradually adapt to the increased pressure. Once at storage depth, divers live within these comfortable, controlled habitats, which include areas for sleeping, eating, and hygiene, often for periods ranging from several days to several weeks.
From the habitat, divers transfer into a diving bell, which is then sealed and deployed to the underwater worksite. The bell is lowered to the designated depth, maintaining the same pressure as the living chambers, ensuring divers remain at constant pressure. Divers then exit the bell to perform their tasks, connected to the bell by an umbilical that supplies breathing gas, hot water for suits, communication, and power for tools. After completing their work, which can last several hours per shift, divers return to the bell and are transported back to the living chambers, remaining under pressure until the mission is complete.
Decompression and Return to Surface
Once the underwater work phase of a saturation dive is finished, divers undergo a single, carefully managed decompression process to safely return to surface pressure. This critical phase occurs within the saturation chambers, which function as hyperbaric decompression facilities. The decompression is performed very slowly to allow the inert gases dissolved in the divers’ tissues to gradually leave the body without forming bubbles. Rapid ascent would cause these gases to come out of solution too quickly, leading to decompression sickness.
The rate of decompression is precisely controlled, typically ranging from 3 to 6 feet of seawater (approximately 0.9 to 1.8 meters) per hour. This slow, continuous reduction in pressure, often with planned rest stops, ensures the safe off-gassing of inert gases through the lungs. Depending on the depth and duration of the saturation dive, the total decompression time can range from several days to over a week. For instance, a dive to 650 feet might require approximately eight days of decompression. Monitoring of the chamber environment, including oxygen partial pressures, is maintained throughout this process to ensure diver safety.