There are two related terms that reflect particular usages rather than technically different types: When used underwater there are two ways to prevent water flooding in when the submersible hyperbaric chamber's hatch is opened.

[citation needed] In addition to the diving bell and hyperbaric chamber, related Pressure Vessels for Human Occupancy (PVHOs) includes the following:[2] As well as transporting divers, a diving chamber carries tools and equipment, high pressure storage cylinders for emergency breathing gas supply, and communications and emergency equipment.

It provides a temporary dry air environment during extended dives for rest, eating meals, carrying out tasks that cannot be done underwater, and for emergencies.

The ability to return to the surface without in-water decompression reduces the risk to the divers if the weather or compromised dynamic positioning forces the support vessel off station.

They have airlocks for underwater entry or to form a watertight seal with hatches on the target structure to effect a dry transfer of personnel.

Rescuing occupants of submarines or submersibles with internal air pressure of one atmosphere requires being able to withstand the huge pressure differential to effect a dry transfer, and has the advantage of not requiring decompression measures on returning to the surface, allowing a more rapid turnaround to continue the rescue effort.

[citation needed] Lightweight portable hyperbaric chambers that can be lifted by helicopter are used by military or commercial diving operators and rescue services to carry one or two divers requiring recompression treatment to a suitable facility.

In cases such as circulatory problems, non-healing wounds, and strokes, adequate oxygen cannot reach the damaged area and the body's healing process is unable to function properly.

[citation needed] If the diver notes significant improvement in symptoms, or the attendant can detect changes in a physical examination, a treatment table is followed.

[citation needed] U.S. Navy Table 9 consists of compression to 45 feet (14 m) with the patient on oxygen, with later decompression to surface pressure.

[citation needed] The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water.

This is used to transfer personnel from portable recompression chambers to multi-person chambers for treatment, and between saturation life support systems and personnel transfer capsules (closed bells) for transport to and from the worksite, and for evacuation of saturation divers to a hyperbaric lifeboat.

[citation needed] Diver training and experimental work requiring exposure to relatively high ambient pressure under controllable and reproducible conditions may be done in a water-filled or partially water-filled hyperbaric chamber, referred to as a wet pot, usually accessed via a dry hyperbaric chamber at the same pressure, with airlock access to the outside.

It is sometimes necessary to transport a diver with severe symptoms of decompression illness to a more suitable facility for treatment, or to evacuate people in a hyperbaric environment which is threatened by a high risk hazard.

The component chambers are mounted on wheeled trolleys and have a design pressure of 110 pounds per square inch (7.6 bar) gauge which is suitable for most of the US Navy treatment schedules that are relevant for bounce dives.

At 1,268 pounds (575 kg) It is not truly portable by manpower in most circumstances, but the wheels make it fairly easy to move around on a horizontal surface.

2 The rescue chamber or hyperbaric lifeboat will generally be recovered for completion of decompression due to the limited onboard life support and facilities.

This preventative measure allowed divers to safely work at greater depths for longer times without developing decompression sickness.

A medical or stores lock may be present to provide access to the main chamber for small items while under pressure.

These PVHO safety codes focus on the systems aspect of the chambers such as life support requirements as well as the acrylic windows.

[28] Viewports are generally provided to allow the operating personnel to visually monitor the occupants, and can be used for hand signalling as an auxiliary emergency communications method.

These are a pressure vessel feature specific to PVHOs due to the need to see the people inside and evaluate their health.

Other material have been attempted, such as glass or synthetic saphhire, but they would consistently fail to maintain their seal at high pressures and cracks would progress rapidly to catastrphophic failure.

[28] A clearly visible dedicated pressure gauge and vent valve must be provided for all hyperbaric trunking and locks that may be closed at both ends, so that outside support staff can be sure that the internal space is depressurised before attempting to disconnect joints.

Either fire extinguishers specially made for hyperbaric environment with non-toxic contents, or a pressurised internal water spray system can be used.

[31][32][33] A caisson gauge is also the type used on a pneumofathometer to monitor diver depth, and is commonly calibrated in msw or fsw for convenient reference to decompression tables.

Accurate monitoring of the pressure in the chamber and associated airlocks is essential for the safety of the occupants and for safe and effective decompression.

Mechanical interlocks that prevent opening airlocks or disconnecting trunking when there is a pressure differential may also be required by law or code of practice.

Chamber gas may be simply vented and flushed if it is air, but helium mixtures are expensive and over long periods very large volumes would be needed, so the chamber gas of a saturation system is recycled by passing it through a carbon dioxide scrubber and other filters to remove odours and excess moisture.

[citation needed] Non-portable chambers are generally constructed from steel,[28] as it is inexpensive, strong and fire resistant.