Divers may use several special types of vehicles and living facilities. These include vehicles that are hoisted and lowered to transport divers to and from deep dive sites, propelled vehicles to increase the diver’s range and endurance (i.e. diver propulsion vehicles [DPVs], often used by technical divers) and machines to carry underwater equipment. The accommodations to be considered include underwater houses and pressurized houses at the surface.
Submersible decompression chambers (SDCs), often called personnel transfer capsules, are used to transport divers and any attendants from the surface to the work site, and they may also be used as a relay station and store for gas and equipment. The most complex SDC may carry the diver at constant pressure from a deck decompression chamber (DDC) to the work site and back. The simplest SDC consists of a bell chamber that is open at the bottom and allows the diver to decompress in a dry environment, exposed to the same pressure as the surrounding water.
Habitats are underwater houses that accommodate divers in air- or gas-filled environments. They are used by divers to rest between excursions. Divers have lived in some of these habitats for weeks at a time.
Deck decompression chambers (DDCs) can be small and used for surface decompression, a procedure that allows a diver to be decompressed in a dry chamber instead of in the water. Larger chambers can be used to treat divers with decompression illness and other diseases that respond to compression, in which case the chamber may be called a recompression chamber.
DDCs are also used to house divers for prolonged periods under elevated pressure. In this case, divers are carried to their work by an SDC or a small submarine that keeps the diver in a pressurized environment. At the end of the job, possibly after several weeks, the pressure in the DDC is lowered slowly to return the diver to atmospheric pressure.
Transport vehicles can carry the divers at normal atmospheric pressure, at ambient pressure in a dry environment or in a wet environment. These include vehicles towed by a boat. A small motor and propeller that pulls the diver along gives increased speed with reduced effort. Some submarines have a lock system to allow divers to leave and enter underwater.
One atmosphere diving equipment, such as the JIM suit, seals the diver in a pressure-resistant compartment. It has flexible arms with tools on the ‘hands’ for the diver to work underwater. The early types of suit had legs that gave the diver the ability to walk on firm surfaces if there was little current. The diver had no control in mid-water and had to be lowered and hoisted from the surface. In other designs, such as the Newtsuit and WASP system, the diver controls a set of propellers that make him or her a cross between a diver and a one-person submarine.
Life support systems are required to provide the occupants of all these vehicles, habitats and chambers with a respirable atmosphere. These work on the same principles as a diver’s breathing apparatus, and in some vehicles the diver may even be wearing a breathing apparatus. The system must be self-contained for transport vehicles, but for habitats and SDCs the gas is generally supplied from the surface.
Gas from the surface can be supplied in a free flow and escape out the bottom or be recirculated through a purifying system. Simple gas purifying systems can involve a hand-powered pump to force gas through a carbon dioxide absorption canister with a manually operated system for adding oxygen. The most complex systems are those found on large submersibles, nuclear submarines and chambers used for deep saturation dives. These have automatic closed systems with provision for removing trace contaminants and odours, and they also regulate temperature, pressure and humidity.
Gas reclaimers are mainly used to recover helium to be used again. They help to lower costs by reducing the amount of gas used. One type cools the gas until the other gases are liquefied, leaving pure helium to be stored and used again. Other types use a chromatographic technique to separate the gases.