Saturation diving system
A saturation diving system is the combined and installed equipment required to support a saturation diving operation. It may be an underwater habitat, or more commonly for commercial diving operations, a hyperbaric habitat complex, known in the industry as a saturation spread, assembled on a surface platform, supported by a range of surface support equipment, some of which is common to other surface-supplied diving activities, and some of which is used mostly or only for saturation diving. Much of the equipment can be classed as life-support equipment, and some of it is required for emergency and rescue functions.
The basic components include living space accommodations for the divers when they are not diving, with sanitation facilities and a means of providing supplies to the occupants. There are also facilities for compression and decompression, treatment of dysbaric maladies, transfer under pressure between accommodation and closed bell transportation modules for transport between the accommodation and workplace, and for emergency evacuation. Units are interconnected by trunking and can be isolated by airlock doors.
Auxiliary and support equipment includes:
- The hyperbaric life support systems
- *Breathing gas supply and distribution, and recycling and purification. The divers use surface-supplied umbilical diving equipment, using a breathing gas suitable for the depth, such as helium and oxygen mixtures, stored in large capacity, high pressure gas storage cylinders.
- *Thermal management and climate control: heating and cooling for the chambers and the divers in the water.
- Diving bell launch and recovery system
- Control rooms for diving operations and saturation system life support
- Diver voice communications systems, which may include helium speech unscramblers
- Built-in breathing systems
- Fire suppression systems
- Hyperbaric evacuation and rescue systems
Saturation diving
Besides the divers in saturation, the diving team includes diving supervisors, surface standby divers and their dive tenders, gas panel operators, life support technicians, and other diving systems technicians. medical support. food and laundry are usually provided by ship's services if available, and locked in and out of the accommodation.
Architecture of a surface saturation facility
Saturation diving systems are made up from a group of pressure vessels for human occupancy, and their support systems. The pressure chambers are subject to rules for life support, operations, maintenance, and structural design. The "saturation system", "saturation complex" or "saturation spread" typically comprises either an underwater habitat or a surface complex which includes one or more living chambers, a transfer chamber, at least one supply lock, and a submersible decompression chamber, which is commonly referred to in commercial diving and military diving as the diving bell, personnel transfer capsule, or submersible decompression chamber. The system can be permanently installed on a ship or ocean platform, but is more commonly capable of being moved from one vessel to another by crane. To facilitate transportation of the components, it is standard practice to construct the components as modular units based on the intermodal container system, some of which may be stackable to save deck space. The entire system is managed from a control room, where pressure, chamber atmosphere and other system parameters are monitored and controlled. The diving bell is the elevator or lift that transfers divers from the accommodations to the work site. Typically, it is mated to the system utilizing a removable clamp and is separated from the transfer chamber shell by a trunking spool through which the divers transfer between bell and transfer chamber. At the completion of a contract or mission, the saturation divers are decompressed gradually back to atmospheric pressure by the slow release of system pressure. The process normally involves only one decompression, thereby mitigating the time-consuming and comparatively risky process of in-water staged decompression, or surface decompression operations normally associated with non-saturation mixed gas diving. More than one living chamber can be linked to the transfer chamber through trunking so that diving teams can be stored at different depths where this is a logistical requirement. Extra chambers can be fitted to transfer personnel into and out of the system while under pressure and to treat divers for decompression sickness if this should be necessary.The divers use surface-supplied umbilical diving equipment, usually utilizing deep diving breathing gas, such as helium and oxygen mixtures, stored in large capacity, high pressure gas storage cylinders. The gas supplies are plumbed to the control room, from where they are routed to supply the system components. The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water. The bell is also fitted with externally mounted breathing gas cylinders for emergency use.
While in the water the divers will often use a hot water suit to protect against the cold. The hot water comes from heaters at the surface and is pumped down to the diver via the bell's umbilical and then through the diver's umbilical.
Accommodation chambers
The accommodation chambers are where the divers live when they are not diving. They include facilities for eating, personal hygiene, sleeping and recreation. It is also where the divers are compressed and decompressed, and where they prepare for diving and clean up after diving. An accommodation chamber may be as small as 100 square feet, but the chamber size of modular systems is mainly constrained by the space available in a 40 ft intermodal container frame for each modular component. The accommodation area is generally made of multiple compartments, each separate unit joined to the rest of the system by short lengths of cylindrical trunking for access. It is usually possible to isolate each compartment from the others using internal pressure doors at each manway and at each external access point. Catering and laundry are provided from outside the system and locked in and out as required. A modular chamber may be 2.3m diameter or less. Accommodation may be provided for up to 24 divers in a large system, which would probably have two 3-diver bells and allow for split level diving.Where a hyperbaric lifeboat or escape module is provided there will be escape trunking fitted between the accommodation and the rescue and escape system module. The rescue and escape module or modules must be sufficient for all divers in saturation, so there may be more than one of them.
Transfer chamber
The transfer chamber, also known as a , is where the bell is mated to the surface saturation system for transfer under pressure. It is a wet surface chamber where divers prepare for a dive and strip off and clean their gear after return. Connection to the bell may be overhead, through the bottom hatch of the bell, or lateral, through a side door. The transfer chamber may also serve as a shower and toilet compartment in a small system. In a more complex system each living chamber may have its own wet pot shower and toilet chamber, which makes split level diving more convenient. A large system with two bells may have two transfer chambers, which can be isolated from each other and used simultaneously at different storage pressures.Personnel transfer capsule
A closed diving bell, also known as personnel transfer capsule or submersible decompression chamber, is used to transport divers between the underwater workplace and the accommodations chambers. The bell is a domed end cylindrical or spherical pressure vessel with a hatch at the bottom, and may mate with the surface transfer chamber at the bottom hatch or at a side door. Bells are usually designed to carry two or three divers, one of whom, the, stays inside the bell at the bottom and is stand-by diver to the working divers. Each diver is supplied by an excursion umbilical from inside the bell. The bell has a set of high pressure gas storage cylinders mounted on the outside containing on-board reserve breathing gas. The on-board gas and main gas supply are distributed from the bell gas panel, which is controlled by the bellman. The bell may have viewports and external lights. The divers' umbilicals are stored on racks inside the bell during transfer, and are tended by the bellman during the dive.Bell handling system
The bell is deployed from a gantry or A-frame, also known as a bell launch and recovery system, on the vessel or platform, using a winch. Deployment may be over the side or through a moon pool.The bell handling system must be able to support the dynamic loads imposed by operating in a range of weather conditions, and must be able to move the bell through the air/water interface in a controlled way, fast enough to avoid excessive movement caused by wave action. It must have sufficient power for fast retrieval of the bell in an emergency, and fine control to facilitate mating of the bell and transfer flange, and to accurately place the bell at the bottom. It must keep the bell clear of the vessel or platform to prevent impact damage or injury. A bell cursor may be used to limit lateral motion through and above the splash zone.
The bell handling system must include a system to move the bell between the mating flange of the transfer chamber and the launch and retrieval position.
Heave compensation gear may be used to maintain a constant operating depth in a seaway.