User:Pbsouthwood/North Sea diving

The history of offshore diving on the Norwegian sector of the North Sea covers an era of rapid development of equipment and procedures, often in response to new requirements for deeper diving in newly opened oilfields, and the failure of existing procedures, which had previously sufficed, to prevent serious accidents. Development was driven by the profit motive and by health and safety requirements, which were not always well coordinated.

Background
The first offshore pretroleum exploration licences were issued for work off the coast of Louisiana in 1945. At this time there were no recognised methods for drilling under water.

Successful trials were conducted in 1946 from a fixed drilling rig in six metres depth ofwater in 1947 The drilling company, Kerr McGee, struck oil after a few weeks and reported that crude oil could be extracted from the seabed, starting the new industry of offshore drilling contractors.

In 1959 a large gas field was discovered at Groningen in the Netherlands, under a geological structure which extended out to sea. This discovery caused the oil companies to become interested in the North Sea. Shell, Esso and Phillips Petroleum started conducting seismic surveys in the Norwegian sector from 1962, and their geological findings indicated that exploratory drilling would be justified. Esso and Shell began exploratory drilling off the Netherlands coast in 1962, and in 1964 drilling on the UK continental shelf was started. Water depths were down to 30 metres and diver intervention was surface oriented diving on air, following well established practice.

Drilling on the Norwegian continental shelf was started in 19 July 1966 from the drilling rig Ocean Traveller, operated by the American contractor ODECO (Ocean Drilling & Exploration Company). Along with sister ship Ocean Viking, also operated by ODECO, it was responsible for most of the exploration wells before Ekofisk was found. Odeco was contracted to various oil companies involved in the first two licensing rounds.

At this time diving in the 70 to 100 m depth range was commonly done as bell-bounce dives with two divers in the bell, a supervisor on deck and a winch operator. The bell remained unpressurised until it reached depth to minimise pressure exposure and decompression obligation. Diving below 50 m was on heliox breathing gas, and the divers used unheated expanded neoprene diving suits, which lost most of their insulating properties at this pressure. Dive times were limited to 45 minutes due to heat loss in the cold water.

Diving depths and procedures for offshore diving were in the experimental and development stages. Initial research on the physiological effects of deep diving were done largely by the US and British navies, but from about 1970, this role was taken on by the diving contractors.

In the mid-1960s the deepest diving was being done off California, where a record was claimed for diving at 117 metres in 1966, using heliox, by Ocean Systems International Inc., a company which was soon to be diving off Norway. Block awards off Norway 1in 1965 and 1968 required drilling in water depths from 50 to 130 metres, which was beyond the acceptable range for air diving, and further out to sea in more demanding weather conditions than in the Gulf of Mexico or California. Rough seas required tough equipment, and the water temperature averages 5 to 7°C throughout the year, and imposed severe limits on in-water decompression time.

Ocean Systems and Compagnie maritime d'expertises (COMEX) had previous experience in offshore diving operations from work on the UK continental shelf before they started operating in the Norway sector. The UK work had included surface oriented surface-supplied and scuba operations, which were practicable due to the relatively shallow depth.

Early equipment and procedures
Divers were deployed from small dive vessels or directly from the drilling rigs on diving stages, and initially decompressed in the water below 12 metres before transferring to a deck decompression chamber for surface decompression on oxygen. The transfer between the 12 m stop and recompression in the chamber had to be completed within 5 minutes to avoid excessive risk of developing symptomatic decompression sickness.

Low intensity work was often done on scuba, with a dive team comprising the diver, a standby diver, and the supervisor, often with an additional diver's attendant.

Standard helmet diving was also used, particularly for work on the seabed or fixed installations, using air or a mixed breathing gas. Decompression was also based on surface decompression in a chamber after the initial in-water stops. A disadvantage of this system was that the standby diver was stationed at the surface: in an emergency the standby diver was significantly delayed in reaching the working diver.

Both Ocean Traveler and Ocean Viking carried deck decompression chambers fitted with connectors so that a pressurised bell could lock onto them for decompression from bell-bounce dives.

The working diver left the bell to do the job, and the other diver, known as the bellman, remained inside as standby diver and to operate the bell gas panel.

On Ocean Viking, the Comex bell supplied the divers with gas from cylinders mounted on the outside of the bell, controlled through the gas panel. There was no surface gas supply. The bell had wired communications with the surface and an electrical cable for lighting, but no heating. There was no communications between the working diver and the surface. Communications between bellman and diver were by pulls on the umbilical hose and in good visibility, by hand signals, visible through the viewports on the bell, illuminated by external floodlights on the bell. The working diver also carried a torch. In poor visibility the floodlights were often turned off because they made it more difficult to see the diver from the bell. Bottom time was still limited with bell bounce dives, so work was often under time pressure.

In the late 1960s and early 1970s, divers wore a tight-fitting rubber dry suit, often choosing the Norwegian "Viking" suit or the British "Dunlop"suit. In 1970 the Swedish "Unisuit" was introduced, which was a looser cut dry suit worn over insulating undergarments, such as the "Helly-Hansen" "woolly bear" undersuit designed for this purpose. The suits often leaked, and when flooded, were less effective for keeping warm, and very heavy when climbing back into the bell.

An alternative was the wetsuit, made from closed cell foam neoprene, which worked in shallow water but was compressed at depth so it became less effective as an insulator. The diver was wetted by the water which penetrated the suit at the cuffs, collar and closures, but restricted flushing out the water warmed by the diver's body heat.

The helium based gas in the bell was also a good conductor of heat, and divers continued to feel cold even after return to the bell. During decompression the bell atmosphere was replaced by air, which felt noticeably warmer, as it is a better thermal insulator.

The main advantage ofclosed bell bounce diving was the the thermal protection of the divers during decompression, and avoiding the critical stage between in-water and deck chamber decompression. The disadvantages were that only one team could decompress at a time in a DDC, more personnel were required, and the procedure was more expensive. Haste and financial considerations tended to push the operators to minimise decompression, and reduce safety margins.

Diving in support of exploratatory drilling
During the exploratory phase, divers worked in support the rig and of drilling operations. Activity increased over the years: one well was drilled in 1966, and 16 in 1969. The diving team on a rig was usually six people, so with five rigs working in 1969, an estimated diving workforce of 30 people would likely have been employed at any given time.

The dive is the diver's means of accessing the job site, where the work is done. The diver must be competent to do the necessary work while diving safely. The work included inspections, repairs, collecting samples, and making inspections, using a wide range of mechanical, hydraulic and electrical tools, flame cutters, and welding equipment. General seamanship skills, and the ability to work in a team are also necessary. Tools might be carried by the diver, carried in a basket or strapped to the outside of the bell, or lowered from the surface as needed.

At the start of a drilling operation divers would be involved in the setup and inspection of a base plate as a foundation for further drilling. During idle days they would do cleaning and maintenance work on the diving equipment, prepare gas mixtures, and practice emergency procedures. The divers were on permanent standby and when drilling problems occurred, might be working for several days with little sleep.

Diver recruitment
When the American drilling companies started working in Norway, they brought American divers with them, but started recruiting British divers fairly soon, as the working language of the oil industry was English, and competent communications under difficult conditions is necessary for diving safety. Norwegian divers were also recruited, who had been trained in the Norwegian Navy - the best diver training available in Norway in the 1960s, and were initially unfamiliar with offshore procedures and equipment.

The American diver training system had a junior diver working under the supervision of an experienced diver and getting theoretical instruction and practical experience instruction in gas mixing and decompression with a heliox mixture.

In September 1968, three of the Norwegian divers were involved as shareholders in founding the first Norwegian diving contractor, 3X or ThreeX. These were Odd Gåskjenn, Gunnar Møllegaard and Leif-Tore Skjerven. Initially, they worked out of a small office and warehouse in Strømsteinen, in Stavanger. In 1969, 3X invested in its first deck decompression chamber, followed in 1971, by its first diving bell with deck decompression chamber, made in Stavanger by AS Alfred Paulsen to a design from 3X, and using a side lock for transfer under pressure to the decompression chamber.

The transition of Ekofisk from exploration to development, and the ongoing exploration on other blocks caused rapid growth of the industry. The number of diving contractors rose to 15 by 1973. Ekofisk development helped 3X and other Norwegian diving companies to become established.

Ekofisk and Frigg
The development of the Ekofisk and Frigg gas fields included constructing and setting up the platforms. Groundbreaking new technology was developed to open these fields to production. Divers performed many essential services, including installing, inspecting and repairing equipment, underwater welding and cutting operations, and helping to lay pipelines and connect components. There was more work to be done than divers to do it, and underwater work became a limiting factor. Drilling operations and other critical work were delayed until divers had done their underwater work. The established procedures of surface-oriented bell-bounce diving were inefficient as they only allowed the diver a short time doing useful work for a long decompression, so saturation diving was adopted for improved efficiency, as shifts were not limited by decompression obligations, and could be changed in the time it took to bring the working divers to the surface, transfer them under pressure to the accommodation chambers, transfer the next shift into the bell and lower them to the worksite. Off shift divers were able to clean up, eat, sleep and relax until their next shift, all at a relatively constant pressure equivalent to the pressure at the worksite for the job in hand. The risky procedure of decompression was only necessary at the end of the tour of duty, which could be weeks long, and there was less rush to decompress, so more conservative, less risky, decompression schedules became reasonably practicable.

Rising oil prices and a demand for stable supplies put considerable pressure on the companies to get the oil-fields into production.