History of underwater diving

The history of

Limitations in the mobility of the surface-supplied systems encouraged the development of both open circuit and closed circuit scuba in the 20th century, which allow the diver a much greater autonomy. These also became popular during World War II for clandestine military operations, and post-war for scientific, search and rescue, media diving, recreational and technical diving. The heavy free-flow surface-supplied copper helmets evolved into lightweight demand helmets, which are more economical with breathing gas, which is particularly important for deeper dives and expensive helium based breathing mixtures, and saturation diving reduced the risks of decompression sickness for deep and long exposures.

An alternative approach was the development of the "single atmosphere" or armoured suit, which isolates the diver from the pressure at depth, at the cost of great mechanical complexity and limited dexterity. The technology first became practicable in the middle 20th century. Isolation of the diver from the environment was taken further by the development of remotely operated underwater vehicles in the late 20th century, where the operator controls the ROV from the surface, and autonomous underwater vehicles, which dispense with an operator altogether. All of these modes are still in use and each has a range of applications where it has advantages over the others, though diving bells have largely been relegated to a means of transport for surface-supplied divers. In some cases, combinations are particularly effective, such as the simultaneous use of surface orientated or saturation surface-supplied diving equipment and work or observation class remotely operated vehicles.

Although the pathophysiology of decompression sickness is not yet fully understood,

Underwater diving was practiced in

The diving bell is one of the earliest types of equipment for underwater work and exploration.^[10] Its use was first described by Aristotle in the 4th century BC: "...they enable the divers to respire equally well by letting down a cauldron, for this does not fill with water, but retains the air, for it is forced straight down into the water."^[11] According to Roger Bacon, Alexander the Great explored the Mediterranean on the authority of Ethicus the astronomer.^{[citation needed]}

Diving bells were developed in the 16th and 17th century as the first significant mechanical aid to underwater diving. They were rigid open-bottomed chambers lowered into the water and ballasted to remain upright and to sink even when full of air.^[12]

The first reliably recorded use of a diving bell was by Guglielmo de Lorena in 1535 to explore Caligula's barges in Lake Nemi.^[13] In 1616, Franz Kessler built an improved diving bell.^{[14]: 693 [15]}

In 1658, Albrecht von Treileben was contracted by King Gustavus Adolphus of Sweden to salvage the warship Vasa, which sank outside Stockholm harbor in about 32 metres (105 ft) of water on its maiden voyage in 1628. Between 1663 and 1665 von Treileben's divers were successful in raising most of the cannon, working from a diving bell with an estimated free air capacity of about 530 litres (120 imp gal; 140 US gal) for periods of about 15 minutes at a time in dark water with a temperature of about 4 °C (39 °F).^[16][17] In late 1686, Sir William Phipps convinced investors to fund an expedition to what is now Haiti and the Dominican Republic to find sunken treasure, despite the location of the shipwreck being based entirely on rumor and speculation. In January 1687, Phipps found the wreck of the Spanish galleon Nuestra Señora de la Concepción off the coast of Santo Domingo. Some sources say they used an inverted container as a diving bell for the salvage operation while others say the crew was assisted by Indian divers in the shallow waters. The operation lasted from February to April 1687 during which time they salvaged jewels, some gold, and 30 tons of silver which, at the time, was worth over £200,000.^[18]

In 1691, Edmond Halley completed plans for a greatly improved diving bell, capable of remaining submerged for extended periods of time, and fitted with a window for the purpose of undersea exploration. The atmosphere was replenished by way of weighted barrels of air sent down from the surface.^[19] In a demonstration, Halley and five companions dived to 60 feet (18 m) in the River Thames, and remained there for over an hour and a half. Improvements made to it over time extended his underwater exposure time to over four hours.^[20][21]

In 1775, Charles Spalding, an Edinburgh confectioner, improved on Edmond Halley's design by adding a system of balance-weights to ease the raising and lowering of the bell, along with a series of ropes for signaling to the surface crew.^[22] Spalding and his nephew, Ebenezer Watson, later suffocated off the coast of Dublin in 1783 doing salvage work in a diving bell of Spalding's design.^[22]

In 1689, Denis Papin had suggested that the pressure and fresh air inside a diving bell could be maintained by a force pump or bellows. His idea was implemented exactly 100 years later by the engineer John Smeaton, who built the first workable diving air pump in 1789.^[14][15]

In 1602, the Spanish military engineer Jerónimo de Ayanz y Beaumont developed the first documented diving dress.^{[clarification needed]} It was tested the same year in the Pisuerga river (Valladolid, Spain).^{[clarification needed]} King Philip the Third attended the demonstration.^[23]

In the early 18th century, the Englishman Andrew Becker made a leather-covered diving suit with a windowed helmet. The suit used a system of tubes for inhaling and exhaling, and Becker demonstrated his suit in the River Thames at London, during which he remained submerged for an hour. These suits were of limited use as there was still no practical system for replenishing the air supply during the dive.^[24]

In 1405,

In 1800, Peter Kreeft presented his diving apparatus to the Swedish king, and used it successfully.^[26][27][28]

In 1819, Augustus Siebe invented an open diving suit which only covered the top portion of the body. The suit included a metal helmet which was riveted to a waterproof jacket that ended below the diver's waist. The suit worked like a diving bell—air pumped into the suit escaped at the bottom edge. The diver was extremely limited in range of motion and had to move about in a more or less upright position. It wasn't until 1837 that Siebe changed the design to a closed system with only the hands left out of the suit with air-tight seals around the wrists.^[29]

The first widely successful diving helmets were produced by the brothers Charles and John Deane in the 1820s.^[30] Inspired by a fire accident he witnessed in a stable in England,^[31] he designed and patented a "Smoke Helmet" to be used by firemen in smoke-filled areas in 1823. The apparatus comprised a copper helmet with an attached flexible collar and garment. A long leather hose attached to the rear of the helmet was to be used to supply air – the original concept being that it would be pumped using a double bellows. A short pipe allowed excess air to escape. The garment was constructed from leather or airtight cloth, secured by straps.^[32]

The brothers had insufficient funds to build the equipment themselves so they sold the patent to their employer Edward Barnard. It was not until 1827 that the first smoke helmets were built by German-born British engineer Augustus Siebe. In 1828 they decided to find another application for their device and converted it into a diving helmet. They marketed the helmet with a loosely attached "diving suit" so that a diver could perform salvage work but only in a full vertical position, otherwise water entered the suit.^[32]

In 1829, the Deane brothers sailed from Whitstable for trials of their new underwater apparatus, establishing the diving industry in the town. In 1834, Charles used his diving helmet and suit in a successful attempt on the wreck of HMS Royal George at Spithead, during which he recovered 28 of the ship's cannon.^[33] In 1836, John Deane recovered from the Mary Rose shipwreck timbers, guns, longbows, and other items.^[34] By 1836, the Deane brothers had produced the world's first diving manual Method of Using Deane's Patent Diving Apparatus which explained in detail the workings of the apparatus and pump, as well as safety precautions.^[35]

In the 1830s, the Deane brothers asked Augustus Siebe to improve their underwater helmet design.

In the early years of the diving suit, divers were often employed for cleaning and maintenance of seagoing vessels which could require the efforts of multiple divers. Ships that did not have diving suits available would commission diving companies to do underwater maintenance of ships' hulls, as a clean hull would increase the speed of the vessel. The average time spent diving for these purposes was between four and seven hours.[38]

The Office of the Admiralty and Marine Affairs adopted the diving suit in the 1860s. Divers duties included underwater repair of vessels, maintenance, and cleaning of propellers, retrieval of lost anchors and chains, and removing seaweed and other fouling from the hull that could hinder movement.^[38]

Royal George, a 100-gun first-rate ship of the line of the Royal Navy, sank undergoing routine maintenance work in 1782. Charles Spalding used a diving bell to recover six iron 12-pounder guns and nine brass 12-pounders in the same year.^[39] In 1839, Major-General Charles Pasley, at the time a colonel of the Royal Engineers, commenced operations. He had previously destroyed some old wrecks in the Thames and intended to break up Royal George with gunpowder charges and then salvage as much as possible using divers.^[40] The Deane brothers were commissioned to perform salvage work on the wreck. Using their new air-pumped diving helmets, they managed to recover about two dozen cannon.^[41]

Pasley's diving salvage operation set many diving milestones, including the first recorded use of the

The US Navy developed a variant of the Mark V system for heliox diving. These were successfully used during the rescue of the crew and salvage of the USS Squalus in 1939. The US Navy Mark V Mod 1 heliox mixed gas helmet is based on the standard Mark V Helmet, with a scrubber canister mounted on the back of the helmet and an inlet gas injection system which recirculates the breathing gas through the scrubber to remove carbon dioxide and thereby conserve helium.^[45][46]

The US Navy replaced the Mark V helmet in 1980 with the Morse Engineering Mark 12 deep water helmet which has a fibreglass shell with a distinctive large rectangular front faceplate for a better field of vision for work. It also has side and top viewports for peripheral vision. This helmet can also be used for mixed gas either for open circuit or as part of a modular semi-closed circuit system, which uses a back mounted recirculating scrubber unit connected to the lower back of the helmet by flexible breathing hoses. The helmet uses a neck dam or can be connected directly to a dry suit, and uses a jocking harness to keep the helmet in position, but is ballasted to provide neutral buoyancy and a centre of gravity at the centre of buoyancy for stability. Airflow is directed over the faceplate to prevent fogging.^[47] Both the Mk V and the Mk 12 were in use in 1981.^[48] The Mk 12 was phased out in 1993.^[49]

The application of the neck dam concept, a development of the dry suit neck seal, to the diving helmet by

A drawback to the equipment pioneered by Deane and Siebe was the requirement for a constant supply of air pumped from the surface. This restricted the movements and range of the diver and was also potentially hazardous as the supply could get cut off for a number of reasons. Early attempts at creating systems that would allow divers to carry a portable breathing gas source did not succeed, as the compression and storage technology was not advanced enough to allow compressed air to be stored in containers at sufficiently high pressures. By the end of the nineteenth century, two basic templates for

In 1912 the German firm

These systems were semi-closed and did not monitor partial pressures of oxygen. They used an injector system to recirculate the breathing gas and did not increase work of breathing.[52]

None of those inventions solved the problem of high pressure when compressed air must be supplied to the diver (as in modern regulators); they were mostly based on a constant-flow supply of the air. The compression and storage technology was not advanced enough to allow compressed air to be stored in containers at sufficiently high pressures to allow useful dive times.

An early diving dress using a compressed air reservoir was designed and built in 1771 by Sieur Fréminet of Paris who conceived an autonomous breathing machine equipped with a reservoir, dragged behind the diver or mounted on his back.^[53][54] Fréminet called his invention machine hydrostatergatique and used it successfully for more than ten years in the harbors of Le Havre and Brest, as stated in the explanatory text of a 1784 painting.^[55][56]

The Frenchman

An important step in the development of open-circuit scuba technology was the invention of the demand regulator in 1864 by the French engineers Auguste Denayrouze and Benoît Rouquayrol. Their suit was the first to supply air to the user by adjusting the flow according to the diver's requirements. The system still had to use surface supply, as the storage cylinders of the 1860s were not able to withstand the high pressures necessary for a practical self-contained unit.^[59]

The first open-circuit scuba system was devised in 1925 by Yves Le Prieur in France. Inspired by the simple apparatus of Maurice Fernez and the freedom it allowed the diver, he conceived an idea to make it free of the tube to the surface pump by using Michelin cylinders as the air supply, containing three litres (0.66 imp gal; 0.79 US gal) of air compressed to 150 kilograms per square centimetre (2,100 psi; 150 bar). The "Fernez-Le Prieur" diving apparatus was demonstrated at the swimming pool of Tourelles in Paris in 1926. The unit consisted of a cylinder of compressed air carried on the back of the diver, connected to a pressure regulator designed by Le Prieur adjusted manually by the diver, with two gauges, one for tank pressure and one for output (supply) pressure. Air was supplied continuously to the mouthpiece and ejected through a short exhaust pipe fitted with a valve as in the Fernez design,^[60] however, the lack of a demand regulator and the consequent low endurance of the apparatus limited the practical use of Le Prieur's device.^{[61]: 1–9}

Le Prieur's design was the first autonomous breathing device used by the first scuba diving clubs in history - Racleurs de fond founded by

In 1942, during the

In 1957, Eduard Admetlla i Lázaro used a version made by Nemrod to descend to a record depth of 100 metres (330 ft).^[68]

Early scuba sets were usually provided with a plain harness of shoulder straps and waist belt. The waist belt buckles were usually quick-release, and shoulder straps sometimes had adjustable or quick-release buckles. Many harnesses did not have a backplate, and the cylinders rested directly against the diver's back. The harnesses of many diving rebreathers made by Siebe Gorman included a large back-sheet of reinforced rubber.^{[citation needed]}

Early scuba divers dived without any buoyancy aid.

The alternative concept, developed in roughly the same time frame was closed-circuit scuba. The body consumes and metabolises only a part of the oxygen in the inhaled air at the surface, and an even smaller fraction when the breathing gas is compressed as it is in ambient pressure systems underwater. A rebreather recycles the used breathing gas, while constantly replenishing it from the supply so that the oxygen level does not get dangerously depleted. The apparatus also has to remove the exhaled carbon dioxide, as a buildup of CO₂ levels would result in respiratory distress due to hypercapnia.^[51]

The earliest known

Sir

In the 1930s,

Lambertsen later suggests that breathing gas mixtures of nitrogen or helium with oxygen greater than in air could be used in scuba to increase the depth range beyond that possible using pure oxygen rebreathers, at the same time reducing the requirement for decompression. In the early 1950s, Lambertsen developed a semiclosed-circuit scuba called the FLATUS I, which continuously added a small flow of oxygen-rich mixed gas to a rebreather circuit. The flow of fresh gas replenished the oxygen depleted by metabolic consumption, and exhaled carbon dioxide was removed in an absorbent canister. The added inert gas was not consumed by the diver, so this amount of gas mixture was exhausted from the breathing loop to maintain a constant volume and an approximately constant mixture in the loop.[49]

Once saturation is achieved, the amount of time needed for

This section needs expansion with: development of the closed bell and locking systems. You can help by adding to it. (April 2024)

The first commercial saturation dives were performed in 1965 by

This section needs expansion. You can help by adding to it. (April 2024)

The

Two English inventors developed diving suits in the early 18th century. In 1715, John Lethbridge constructed an enclosed "diving engine" to use in savage work. Essentially a pressure resistant air-filled wooden barrel about 6 feet (1.8 m) in length with two holes for the diver's arms sealed with leather cuffs, and a 4-inch (100 mm) viewport of thick glass.^[91] This suit was not surface supplied. Air was sealed in with the diver at the surface before the dive, and lasted up to half an hour at a push. After testing this machine in his garden pond specially built for the purpose, Lethbridge dived on a number of wrecks. It was reportedly used to dive as deep as 60 feet (18 m), and was used to salvage substantial quantities of silver from the wreck of the East Indiaman Vansittart which sank in 1718 off the Cape Verde islands.^[92] A similar suit made of copper, with a curved profile, was made by Jacob Rowe who also worked on the Vansittart.^[93]

Lethbridge became fairly wealthy as a result of his salvages. One of his better-known recoveries was on the Dutch Slot ter Hooge, which had sunk off Madeira with over three tons of silver on board.^[15] Lethbridge salvaged several Dutch East Indiamen under contract to the VOC, some at the Cape of Good Hope. Jacob Rowe moved north and worked on wrecks off the north coast of Scotland "Vansittart".^[93]

The first armored suit with real joints, designed as leather pieces with rings in the shape of a spring (also known as accordion joints), was designed by Englishman W. H. Taylor in 1838. The diver's hands and feet were covered with leather. Taylor also devised a ballast tank attached to the suit that could be filled with water to attain negative buoyancy. While it was patented, the suit was never actually produced. It is considered that its weight and bulk would have rendered it nearly immobile underwater.^[92]

Lodner D. Phillips designed the first wholly enclosed ADS in 1856. His design comprised a barrel-shaped upper torso with domed ends and included ball and socket joints in the articulated arms and legs. The arms had joints at shoulder and elbow, and the legs at knee and hip. The suit included a ballast tank, a viewing port, an entrance through a manhole cover on top, a hand-cranked propeller, and rudimentary manipulators at the ends of the arms. Air was to be supplied from the surface via a hose. There is no indication, however, Phillips' suit was ever constructed.^[92]

The first properly anthropomorphic design of ADS, built by the Carmagnolle brothers of

American designer MacDuffy constructed the first suit to use ball bearings to provide joint movement in 1914; it was tested in New York to a depth of 214 feet (65 m), but was not very successful. A year later, Harry L. Bowdoin of Bayonne, New Jersey, made an improved ADS with oil-filled rotary joints. The joints use a small duct to the interior of the joint to allow equalization of pressure. The suit was designed to have four joints in each arm and leg, and one joint in each thumb, for a total of eighteen. Four viewing ports and a chest-mounted lamp were intended to assist underwater vision. Unfortunately, there is no evidence that Bowdoin's suit was ever built or that it would have worked if it had been.^[92]

Atmospheric diving suits built by German firm Neufeldt and Kuhnke were used during the salvage of gold and silver bullion from the wreck of the British ship

In 1924, the Reichsmarine tested the second generation of the Neufeldt and Kuhnke suit to 530 feet (160 m), but limb movement was very difficult and the joints were judged not to be fail-safe, in that if they were to fail, there was a possibility that the suit's integrity would be violated. However, these suits were used by the Germans as armored divers during World War II and were later taken by the Western Allies after the war.

In 1952, Alfred A. Mikalow constructed an ADS employing ball and socket joints, specifically for the purpose of locating and salvaging sunken treasure. The suit was reportedly capable of diving to depths of 1,000 feet (300 m) and was used successfully to dive on the sunken vessel

Although various atmospheric suits had been developed during the Victorian era, none of these suits had been able to overcome the basic design problem of constructing a joint that would remain flexible and watertight at depth without seizing up under pressure.^{[citation needed]}

Pioneering British diving engineer, Joseph Salim Peress, invented the first truly usable atmospheric diving suit, the Tritonia, in 1932 and was later involved in the construction of the famous JIM suit. Having a natural talent for engineering design, he challenged himself to construct an ADS that would keep divers dry and at atmospheric pressure, even at great depth. In 1918, Peress began working for WG Tarrant at Byfleet, United Kingdom, where he was given the space and tools to develop his ideas about constructing an ADS. His first attempt was an immensely complex prototype machined from solid stainless steel.

In 1923, Peress was asked to design a suit for salvage work on the wreck of SS Egypt which had sunk in the English Channel. He declined, on the grounds that his prototype suit was too heavy for a diver to handle easily, but was encouraged by the request to begin work on a new suit using lighter materials. By 1929 he believed he had solved the weight problem, by using cast magnesium instead of steel, and had also managed to improve the design of the suit's joints by using a trapped cushion of oil to keep the surfaces moving smoothly. The oil, which was virtually non-compressible and readily displaceable, would allow the limb joints to move freely at depths of 200 fathoms (1,200 ft; 370 m), where the pressure was 520 psi (35 atm). Peress claimed that the Tritonia suit could function at 1,200 ft (370 m) although this was never proven.^[96]

In 1930, Peress revealed the Tritonia suit.^[97] By May it had completed trials and was publicly demonstrated in a tank at Byfleet. In September Peress' assistant Jim Jarret dived in the suit to a depth of 123 m (404 ft) in Loch Ness. The suit performed perfectly, the joints proving resistant to pressure and moving freely even at depth. The suit was offered to the Royal Navy which turned it down, stating that Navy divers never needed to descend below 90 m (300 ft). In October 1935, Jarret made a successful deep dive to more than 90 m (300 ft) on the wreck of RMS Lusitania off south Ireland, followed by a shallower dive to 60 metres (200 ft) in the English Channel in 1937 after which, due to lack of interest, the Tritonia suit was retired.

The development in atmospheric pressure suits stagnated in the 1940s through 1960s, as efforts were concentrated on solving the problems of deep diving by dealing with the physiological problems of ambient pressure diving instead of avoiding them by isolating the diver from the pressure. Although the advances in ambient pressure diving (in particular, with scuba gear) were significant, the limitations brought renewed interest to the development of the ADS in the late 1960s.^[96]

The Tritonia suit spent about 30 years in an engineering company's warehouse in Glasgow, where it was discovered, with Peress' help, by two partners in the British firm Underwater Marine Equipment, Mike Humphrey and Mike Borrow, in the mid-1960s.^[96][98][99] UMEL would later classify Peress' suit as the "A.D.S Type I", a designation system that would be continued by the company for later models. In 1969, Peress was asked to become a consultant to the new company created to develop the JIM suit, named in honour of the diver Jim Jarret.^[100]

The Tritonia suit was upgraded into the first JIM suit, completed in November 1971. This suit underwent trials aboard HMS Reclaim in early 1972, and in 1976, the JIM suit set a record for the longest working dive below 490 feet (150 m), lasting five hours and 59 minutes at a depth of 905 feet (276 m).^[101][90] The first JIM suits were constructed from cast magnesium for its high strength-to-weight ratio and weighed approximately 1,100 pounds (500 kg) in air including the diver. They were 6 feet 6 inches (2.0 m) in height and had a maximum operating depth of 1,500 feet (460 m). The suit had a positive buoyancy of 15 to 50 pounds (6.8 to 22.7 kg). Ballast was attached to the suit's front and could be jettisoned from within, allowing the operator to ascend to the surface at approximately 100 feet (30 m) per minute.^[102] The suit also incorporated a communication link and a jettisonable umbilical connection. The original JIM suit had eight annular oil-supported universal joints, one in each shoulder and lower arm, and one at each hip and knee. The JIM operator received air through an oral/nasal mask that attached to a lung-powered scrubber that had a life-support duration of approximately 72 hours.^[100] Operations in arctic conditions with water temperatures of -1.7 °C for over five hours were successfully carried out using woolen thermal protection and neoprene boots. In 30 °C water, the suit was reported to be uncomfortably hot during heavy work.^[103]

As technology improved and operational knowledge grew, Oceaneering upgraded its fleet of JIMs. The magnesium construction was replaced with

In addition to upgrades to the JIM design, other variations of the original suit were constructed. The first, named the SAM Suit (Designated A.D.S III), was a completely aluminium model. A smaller and lighter suit, it was more anthropomorphic than the original JIMs and was depth-rated to 1,000 feet (300 m). Attempts were made to limit corrosion by the use of a chromic anodizing coating applied to the arm and leg joints, which gave them an unusual green color. The SAM suit stood at 6 feet 3 inches (1.91 m) in height, and had a life-support duration of 20 hours. Only three SAM suits would be produced by UMEL before the design was shelved. The second, named the JAM suit (Designated A.D.S IV), was constructed of GRP and was depth-rated for around 2,000 feet (610 m).^[104]

In 1987, the "Newtsuit" was developed by the Canadian engineer Phil Nuytten.^[102] The Newtsuit is constructed to function like a "submarine you can wear", allowing the diver to work at normal atmospheric pressure even at depths of over 1,000 feet (300 m). Made of wrought aluminium, it had fully articulated joints so the diver can move more easily underwater. The life-support system provides six to eight hours of air, with an emergency backup supply of an additional 48 hours. The Newtsuit was used to salvage the bell from the wreck of SS Edmund Fitzgerald in 1995. A more recent design by Nuytten is the Exosuit, a relatively lightweight suit intended for marine research.^[105] It was first used in 2014 at the Bluewater and Antikythera underwater research expeditions.^[90][106]

The ADS 2000 was developed jointly with OceanWorks International and the US Navy in 1997,^[107] as an evolution of the Newtsuit to meet US Navy requirements. The ADS2000 provides increased depth capability for the US Navy's Submarine Rescue Program. Manufactured from forged T6061 aluminum alloy it uses an advanced articulating joint design based on the Newtsuit joints. Capable of operating in up to 2,000 feet (610 m) of seawater for a normal mission of up to six hours it has a self-contained, automatic life support system.^[108] Additionally, the integrated dual thruster system allows the pilot to navigate easily underwater. It became fully operational and certified by the US Navy off southern California on 1 August 2006, when a diver submerged to 2,000 feet (610 m).^[109]

• 
  Side view of Exosuit
• 
  Back view of Exosuit

A change in pressure may have an immediate effect on the ears and sinuses, causing pain and leading to congestion, edema, hemorrhaging, and temporary to permanent hearing impairment. These effects have been familiar to breath-hold divers since antiquity and are avoided by equalisation techniques. Reduction of ambient pressure during ascent can cause overpressure injury to internal gas spaces if not allowed to freely equalise. Health effects in divers include damage to the joints and bones similar to symptoms attributed to caisson disease in compressed air workers, which was found to be caused by too rapid a decompression to atmospheric pressure after long exposure to a pressurised environment^[110]

When a diver descends in the water column, the

The first recorded experimental work related to decompression was conducted by Robert Boyle, who subjected experimental animals to reduced ambient pressure by use of a primitive vacuum pump. In the earliest experiments, the subjects died from asphyxiation, but in later experiments, signs of what was later to become known as decompression sickness were observed. Later, when technological advances allowed the use of pressurisation of mines and caissons to exclude water ingress, miners were observed to present symptoms of what would become known as caisson disease, the bends, and decompression sickness. Once it was recognized that the symptoms were caused by gas bubbles and that recompression could relieve the symptoms, further work showed that it was possible to avoid symptoms by slow decompression, and subsequently, various theoretical models have been derived to predict low-risk decompression profiles and treatment of decompression sickness.

By the late 19th century, as salvage operations became deeper and longer, an unexplained malady began afflicting the divers; they would suffer breathing difficulties, dizziness, joint pain, and paralysis, sometimes leading to death. The problem was already well known among workers building tunnels and bridge footings operating under pressure in caissons and was initially called "

French

Research on decompression was continued by the US Navy. The C&R tables were published in 1915, and a large number of experimental dives done in the 1930s, which led to the 1937 tables. Surface decompression and oxygen use were also researched in the 1930s, and the US Navy 1957 tables developed to deal with problems found in the 1937 tables.[116]

In 1965, Hugh LeMessurier and Brian Hills published their paper, A thermodynamic approach arising from a study on Torres Strait diving techniques, which suggested that decompression by conventional models results in bubble formation which is then eliminated by re-dissolving at the decompression stops which is slower than off-gassing while still in solution. This indicates the importance of minimizing bubble phase for efficient gas elimination.^[117][118]

M.P. Spencer showed that doppler ultrasonic methods can detect venous bubbles in asymptomatic divers,^[119] and Andrew Pilmanis showed that safety stops reduced bubble formation.^[116] In 1981 D.E. Yount described the Varying Permeability Model, proposing a mechanism of bubble formation.^[120] Several other bubble models followed.^{[116][121][122]}