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138-552: The Tektite habitat was an underwater laboratory which was the home to divers during Tektite I and II programs. The Tektite program was the first scientists-in-the-sea program sponsored nationally. The habitat capsule was placed in Great Lameshur Bay , Saint John, U.S. Virgin Islands in 1969 and again in 1970. "Tektite III" refers to an educational project in the 1980s, using the original habitat capsule used by scientists, which

276-751: A Villanova electrical engineering graduate who served as Habitat Engineer. The Tektite II missions were the first to undertake in-depth ecological studies from a saturation habitat. Medical and human research oversight for Tektite II was well documented in a series of reports covering a project overview, saturation diving, lessons learned from Tektite I, application to Tektite II, medical responsibilities and psychological monitoring, medical supervision duties medical and biological objectives project logistics, lessons learned, excursions to deeper depths from storage pressure, decompression tables , general medical observations, psychological observations, blood changes and general program conclusions. There were nine studies on

414-403: A starfish -shaped house for 30 days. The undersea living experiment also had two other structures, one a submarine hangar that housed a small, two-man submarine named SP-350 Denise , often referred to as the "diving saucer" for its resemblance to a science fiction flying saucer, and a smaller "deep cabin" where two oceanauts lived at a depth of 30 metres (100 ft) for a week. They were among

552-411: A "no-decompression" dive is a dive that needs no decompression stops during the ascent according to the chosen algorithm or tables, and relies on a controlled ascent rate for the elimination of excess inert gases. In effect, the diver is doing continuous decompression during the ascent. The "no-stop limit", or "no-decompression limit" (NDL), is the time interval that a diver may theoretically spend at

690-443: A certain generosity can not hurt. In an underwater habitat, observations can be carried out at any hour to study the behavior of both diurnal and nocturnal organisms. Habitats in shallow water can be used to accommodate divers from greater depths for a major portion of the decompression required. This principle was used in the project Conshelf II. Saturation dives provide the opportunity to dive with shorter intervals than possible from

828-446: A dedicated decompression gas, as they are usually not more than two to three minutes long. A study by Divers Alert Network in 2004 suggests that addition of a deep (c. 15 m) as well as a shallow (c. 6 m) safety stop to a theoretically no-stop ascent will significantly reduce decompression stress indicated by precordial doppler detected bubble (PDDB) levels. The authors associate this with gas exchange in fast tissues such as

966-414: A deep stop profile suggests that the deep stops schedule had a greater risk of DCS than the matched (same total stop time) conventional schedule. The proposed explanation was that slower gas washout or continued gas uptake offset benefits of reduced bubble growth at deep stops. Profile-dependent intermediate stops (PDIS)s are intermediate stops at a depth above the depth at which the leading compartment for

1104-491: A degree of conservatism built into their recommendations. Divers can and do suffer decompression sickness while remaining inside NDLs, though the incidence is very low. On dive tables a set of NDLs for a range of depth intervals is printed in a grid that can be used to plan dives. There are many different tables available as well as software programs and calculators, which will calculate no decompression limits. Most personal decompression computers (dive computers) will indicate

1242-510: A depth of 100 metres (330 ft). In Germany, the Helgoland UWL was the first habitat to be used in cold water, the Tektite stations were more spacious and technically more advanced. The most ambitious project was Sealab III, a rebuild of Sealab II, which was to be operated at 186 metres (610 ft). When one of the divers died in the preparatory phase due to human error, all similar projects of

1380-663: A depth of 43-foot (13 m). Tektite II comprised ten missions lasting 10–20 days with four scientists and an engineer on each mission, including one all-female team. Ichthyologist and director of the Australian Museum , Frank Talbot , joined one of the missions. The fifth mission, designated Mission 6-50, was the first all-female saturation dive team. The elite team of scientist-divers included Renate Schlentz True of Tulane , team leader Sylvia Earle , Ann Hurley Hartline and Alina Szmant, graduate students at Scripps Institution of Oceanography , and Margaret Ann "Peggy" Lucas Bond,

1518-571: A detachment from Amphibious Construction Battalion 2 augmented by an additional 17 Seabee divers from both the Atlantic and Pacific fleets as well as the 21st NCR began the installation of the habitat in Great Lameshur Bay in the U. S. Virgin Islands . They had it completed on February 12. On February 15, 1969, three days later, four U.S. Department of Interior scientists (Ed Clifton, Conrad Mahnken, Richard Waller and John VanDerwalker) descended to

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1656-638: A diving chamber, culminating in the first aquanaut , Robert Sténuit , spending over 24 hours at a depth of 200 feet (61 m). Also inspired by Genesis, Jacques-Yves Cousteau conducted the first Conshelf project in France in 1962 where two divers spent a week at a depth of 10 metres (33 ft), followed in 1963 by Conshelf II at 11 metres (36 ft) for a month and 25 metres (82 ft) for two weeks. In June 1964, Robert Sténuit and Jon Lindberg spent 49 hours at 126m in Link's Man-in-the-Sea II project. The habitat

1794-405: A generation of smaller, less ambitious yet longer-term undersea habitats primarily for marine research purposes. Conshelf I (Continental Shelf Station), constructed in 1962, was the first inhabited underwater habitat. Developed by Cousteau to record basic observations of life underwater, Conshelf I was submerged in 10 metres (33 ft) of water near Marseille , and the first experiment involved

1932-410: A given depth without having to perform any decompression stops while surfacing. The NDL helps divers plan dives so that they can stay at a given depth for a limited time and then ascend without stopping while still avoiding an unacceptable risk of decompression sickness. The NDL is a theoretical time obtained by calculating inert gas uptake and release in the body, using a decompression model such as

2070-455: A new world's record for saturated diving by a single team. On 15 April 1969, the aquanaut team returned to the surface after performing 58 days of marine scientific studies. More than 19 hours of decompression were needed to safely return the team to the surface. Inspired in part by NASA's budding Skylab program and an interest in better understanding the effectiveness of scientists working under extremely isolated living conditions, Tektite

2208-429: A personal dive computer to allow them to avoid obligatory decompression, while allowing considerable flexibility of dive profile. A surface supplied diver will normally have a diving supervisor at the control point who monitors the dive profile and can adjust the schedule to suit any contingencies as they occur. A diver missing a required decompression stop increases the risk of developing decompression sickness. The risk

2346-669: A platform for a television game show. It was deployed for the first time in September 2005 for ten days, and six aquanauts lived in the complex for 14 days in 2007. The MarineLab underwater laboratory was the longest serving seafloor habitat in history, having operated continuously from 1984 to 2018 under the direction of aquanaut Chris Olstad at Key Largo , Florida. The seafloor laboratory has trained hundreds of individuals in that time, featuring an extensive array of educational and scientific investigations from United States military investigations to pharmaceutical development. Beginning with

2484-416: A precaution against any unnoticed dive computer malfunction, diver error or physiological predisposition to decompression sickness, many divers do an extra "safety stop" (precautionary decompression stop) in addition to those prescribed by their dive computer or tables. A safety stop is typically 1 to 5 minutes at 3 to 6 metres (10 to 20 ft). They are usually done during no-stop dives and may be added to

2622-774: A productive future, however, as Cousteau later repudiated his support for such exploitation of the sea and put his efforts toward conservation. It was also found in later years that industrial tasks underwater could be more efficiently performed by undersea robot devices and men operating from the surface or from smaller lowered structures, made possible by a more advanced understanding of diving physiology. Still, these three undersea living experiments did much to advance man's knowledge of undersea technology and physiology, and were valuable as " proof of concept " constructs. They also did much to publicize oceanographic research and, ironically, usher in an age of ocean conservation through building public awareness. Along with Sealab and others, it spawned

2760-790: A project initiated in 1973, MarineLab, then known as Midshipman Engineered & Designed Undersea Systems Apparatus (MEDUSA), was designed and built as part of an ocean engineering student program at the United States Naval Academy under the direction of Dr. Neil T. Monney. In 1983, MEDUSA was donated to the Marine Resources Development Foundation (MRDF), and in 1984 was deployed on the seafloor in John Pennekamp Coral Reef State Park, Key Largo, Florida. The 2.4-by-4.9-metre (8 by 16 ft) shore-supported habitat supports three or four persons and

2898-462: A remaining no decompression limit at the current depth during a dive. The displayed interval is continuously revised to take into account changes of depth and elapsed time, and where relevant changes of breathing gas. Dive computers also usually have a planning function which will display the NDL for a chosen depth taking the diver's recent decompression history, as recorded by that computer, into account. As

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3036-470: A repetitive dive. This means that the decompression required for the dive is influenced by the diver's decompression history. Allowance must be made for inert gas preloading of the tissues which will result in them containing more dissolved gas than would have been the case if the diver had fully equilibrated before the dive. The diver will need to decompress longer to eliminate this increased gas loading. The surface interval (SI) or surface interval time (SIT)

3174-504: A series of decompression stops, each stop being longer but shallower than the previous stop. A deep stop was originally an extra stop introduced by divers during ascent, at a greater depth than the deepest stop required by their computer algorithm or tables. This practice is based on empirical observations by technical divers such as Richard Pyle , who found that they were less fatigued if they made some additional stops for short periods at depths considerably deeper than those calculated with

3312-479: A steel cylinder, doing several excursions. In June 1964 Stenuit and Jon Lindbergh spent 49 hours at a depth of 126 metres (413 ft) in the Man-in-the-Sea II program. The habitat consisted of a submerged portable inflatable dwelling (SPID). Conshelf, short for Continental Shelf Station, was a series of undersea living and research stations undertaken by Jacques Cousteau's team in the 1960s. The original design

3450-399: A surface decompression schedule or a treatment table. If the diver develops symptoms in the chamber, treatment can be started without further delay. A delayed stop occurs when the ascent rate is slower than the nominal rate for a table. A computer will automatically allow for any theoretical ingassing of slow tissues and reduced rate of outgassing for fast tissues, but when following a table,

3588-414: A teaching tool. By 1980, the habitat was fully restored and certified to be used underwater, and named Tektite III; however, funds for actually submerging and operating the habitat again were not available. While the habitat was on display at Fort Mason, many school children were taken through the habitat free of charge by volunteers. Lack of funds ended the project and the habitat was moved to storage along

3726-471: A team of two spending seven days in the habitat. The two oceanauts, Albert Falco and Claude Wesly , were expected to spend at least five hours a day outside the station, and were subject to daily medical exams. Conshelf Two , the first ambitious attempt for men to live and work on the sea floor, was launched in 1963. In it, a half-dozen oceanauts lived 10 metres (33 ft) down in the Red Sea off Sudan in

3864-472: A trimix dive, and oxygen rich heliox blends after a heliox dive, and these may reduce risk of isobaric counterdiffusion complications. Doolette and Mitchell showed that when a switch is made to a gas with a different proportion of inert gas components, it is possible for an inert component previously absent, or present as a lower fraction, to in-gas faster than the other inert components are eliminated (inert gas counterdiffusion), sometimes resulting in raising

4002-434: A warning and additional decompression stop time to compensate. Decompression status is the assumed gas loading of the diver's tissues, based on the chosen decompression model , and either calculated by a dive computer or estimated from dive tables by the diver or diving supervisor, and an indication of the decompression stress that will be incurred by decompressing to a lower ambient pressure. The decompression status of

4140-436: Is a high concentration. The length of the stops is also strongly influenced by which tissue compartments are assessed as highly saturated. High concentrations in slow tissues will indicate longer stops than similar concentrations in fast tissues. Shorter and shallower decompression dives may only need one single short shallow decompression stop, for example, 5 minutes at 3 metres (10 ft). Longer and deeper dives often need

4278-518: Is also calculated and recorded, and used to determine the decompression schedule. A surface supplied diver may also carry a bottom timer or decompression computer to provide an accurate record of the actual dive profile, and the computer output may be taken into account when deciding on the ascent profile. The dive profile recorded by a dive computer would be valuable evidence in the event of an accident investigation. Scuba divers can monitor decompression status by using maximum depth and elapsed time in

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4416-581: Is also closely connected to the history of saturation diving . The original inspiration for the development of underwater habitats was the work of George F. Bond , who investigated the physiological and medical effects of hyperbaric saturation in the Genesis project between 1957 and 1963. Edwin Albert Link started the Man-in-the-Sea project in 1962, which exposed divers to hyperbaric conditions underwater in

4554-438: Is considered in some models to be effectively complete after 12 hours, while other models show it can take up to, or even more than 24 hours. The depth and duration of each stop is calculated to reduce the inert gas excess in the most critical tissues to a concentration which will allow further ascent without unacceptable risk. Consequently, if there is not much dissolved gas, the stops will be shorter and shallower than if there

4692-727: Is divided into a laboratory, a wet-room, and a 1.7-metre-diameter (5 ft 7 in) transparent observation sphere. From the beginning, it has been used by students for observation, research, and instruction. In 1985, it was renamed MarineLab and moved to the 9-metre-deep (30 ft) mangrove lagoon at MRDF headquarters in Key Largo at a depth of 8.3 metres (27 ft) with a hatch depth of 6 m (20 ft). The lagoon contains artifacts and wrecks placed there for education and training. From 1993 to 1995, NASA used MarineLab repeatedly to study Controlled Ecological Life Support Systems (CELLS). These education and research programs qualify MarineLab as

4830-428: Is generally allowed for in decompression planning by assuming a maximum descent rate specified in the instructions for the use of the tables, but it is not critical. Descent slower than the nominal rate reduces useful bottom time, but has no other adverse effect. Descent faster than the specified maximum will expose the diver to greater ingassing rate earlier in the dive, and the bottom time must be reduced accordingly. In

4968-461: Is generally not the fastest compartment except in very short dives, for which this model does not require an intermediate stop. The 8 compartment Bühlmann - based UWATEC ZH-L8 ADT MB PMG decompression model in the Scubapro Galileo dive computer processes the dive profile and suggests an intermediate 2-minute stop that is a function of the tissue nitrogen loading at that time, taking into account

5106-403: Is important to check how bottom time is defined for the tables before they are used. For example, tables using Bühlmann's algorithm define bottom time as the elapsed time between leaving the surface and the start of the final ascent at 10 metres per minute , and if the ascent rate is slower, then the excess of the ascent time to the first required decompression stop needs to be considered part of

5244-429: Is known as staged decompression. The ascent rate and the depth and duration of the stops are integral parts of the decompression process. The advantage of staged decompression is that it is far easier to monitor and control than continuous decompression. A decompression stop is the period a diver must spend at a relatively shallow constant depth during ascent after a dive to safely eliminate absorbed inert gases from

5382-435: Is limited by oxygen toxicity . In open circuit scuba the upper limit for oxygen partial pressure is generally accepted as 1.6 bar, equivalent to a depth of 6 msw (metres of sea water), but in-water and surface decompression at higher partial pressures is routinely used in surface supplied diving operation, both by the military and civilian contractors, as the consequences of CNS oxygen toxicity are considerably reduced when

5520-401: Is made at the recommended rate until the diver reaches the depth of the first stop. The diver then maintains the specified stop depth for the specified period, before ascending to the next stop depth at the recommended rate, and follows the same procedure again. This is repeated until all required decompression has been completed and the diver reaches the surface. The intermittent ascents before

5658-508: Is not easy to sharply define the term "underwater laboratory". One may argue whether Link's diving chamber which was used in the "Man-in-Sea I" project, may be called an underwater laboratory. But the Bentos 300, planned by the Soviets, is not so easy to classify as it has a certain ability to maneuver. Therefore, the possibility exists that this diving hull is classified elsewhere as a submersible. Well,

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5796-509: Is related to the depth and duration of the missed stops. The usual causes for missing stops are not having enough breathing gas to complete the stops or accidentally losing control of buoyancy . An aim of most basic diver training is to prevent these two faults. There are also less predictable causes of missing decompression stops. Diving suit failure in cold water may force the diver to choose between hypothermia and decompression sickness . Diver injury or marine animal attack may also limit

5934-462: Is seldom known with any accuracy, making the decision more difficult for the divers in the water. Continuous decompression is decompression without stops. Instead of a fairly rapid ascent rate to the first stop, followed by a period at static depth during the stop, the ascent is slower, but without officially stopping. In theory this may be the optimum decompression profile. In practice it is very difficult to do manually, and it may be necessary to stop

6072-577: Is the time spent by a diver at surface pressure after a dive during which inert gas which was still present at the end of the dive is further eliminated from the tissues. This continues until the tissues are at equilibrium with the surface pressures. This may take several hours. In the case of the US Navy 1956 Air tables, it is considered complete after 12 hours, The US Navy 2008 Air tables specify up to 16 hours for normal exposure. but other algorithms may require more than 24 hours to assume full equilibrium. For

6210-404: Is towards the use of dive computers to calculate the decompression obligation in real time, using depth and time data automatically input into the processing unit, and continuously displayed on the output screen. Dive computers have become quite reliable, but can fail in service for a variety of reasons, and it is prudent to have a backup system available to estimate a reasonable safe ascent if

6348-452: Is used for a range of applications, including some structures that are not exclusively underwater while operational, but all include a significant underwater component. There may be some overlap between underwater habitats and submersible vessels, and between structures which are completely submerged and those which have some part extending above the surface when in operation. In 1970 G. Haux stated: At this point it must also be said that it

6486-487: Is used to derive the appropriate decompression schedule for the planned dive. Equivalent residual times can be derived for other inert gases. These calculations are done automatically in personal diving computers, based on the diver's recent diving history, which is the reason why personal diving computers should not be shared by divers, and why a diver should not switch computers without a sufficient surface interval (more than 24 hours in most cases, up to 4 days, depending on

6624-426: Is used, and some concepts are common to all decompression procedures. In particular, all types of surface oriented diving benefited significantly from the acceptance of personal dive computers in the 1990s, which facilitated decompression practice and allowed more complex dive profiles at acceptable levels of risk. Decompression in the context of diving derives from the reduction in ambient pressure experienced by

6762-457: Is usually done by specifying a maximum ascent rate compatible with the decompression model chosen. This will be specified in the decompression tables or the user manual for the decompression software or personal decompression computer. The instructions will usually include contingency procedures for deviation from the specified rate, both for delays and exceeding the recommended rate. Failure to comply with these specifications will generally increase

6900-522: The Bühlmann decompression algorithm . Although the science of calculating these limits has been refined over the last century, there is still much that is unknown about how inert gases enter and leave the human body, and the NDL may vary between decompression models for identical initial conditions. In addition, every individual's body is unique and may absorb and release inert gases at different rates at different times. For this reason, dive tables typically have

7038-546: The Florida Keys National Marine Sanctuary . It is deployed on the ocean floor 62 feet (19 m) below the surface and next to a deep coral reef named Conch Reef . Aquarius is one of three undersea laboratories in the world dedicated to science and education. Two additional undersea facilities, also located in Key Largo, Florida , are owned and operated by Marine Resources Development Foundation. Aquarius

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7176-624: The German Oceanographic Museum where it can be visited at the Nautineum , a branch of the museum in Stralsund . Bentos-300 (Bentos minus 300) was a maneuverable Soviet submersible with a diver lockout facility that could be stationed at the seabed. It was able to spend two weeks underwater at a maximum depth of 300m with about 25 people on board. Although announced in 1966, it had its first deployment in 1977. [1] There were two vessels in

7314-834: The Hydrolab Journal . Dr. William Fife spent 28 days in saturation, performing physiology experiments on researchers such as Dr. Sylvia Earle . The habitat was decommissioned in 1985 and placed on display at the Smithsonian Institution 's National Museum of Natural History in Washington, D.C. As of 2017 , the habitat is located at the NOAA Auditorium and Science Center at National Oceanic and Atmospheric Administration (NOAA) headquarters in Silver Spring, Maryland. The Engineering Design and Analysis Laboratory Habitat

7452-592: The Mediterranean Sea near the Cap Ferrat lighthouse, between Nice and Monaco, for three weeks. In this effort, Cousteau was determined to make the station more self-sufficient, severing most ties with the surface. A mock oil rig was set up underwater, and divers successfully performed several industrial tasks. SEALAB I, II, and III were experimental underwater habitats developed by the United States Navy in

7590-471: The Oakland Estuary in 1984. After several years, the habitat again deteriorated. In 1991, the habitat was dismantled by welding school students and the metal was recycled. Underwater habitat An underwater habitat has to meet the needs of human physiology and provide suitable environmental conditions, and the one which is most critical is breathing air of suitable quality . Others concern

7728-652: The Office of Naval Research and the United States Department of the Interior . On 15 February 1969, four Department of the Interior scientists (Ed Clifton, Conrad Mahnken, Richard Waller and John VanDerwalker) descended to the ocean floor in Great Lameshur Bay in the United States Virgin Islands to begin an ambitious diving project dubbed "Tektite I". By 18 March 1969, the four aquanauts had established

7866-512: The ecology of coral reef fishes carried out during the Tektite series: A goal of the Tektite program was to prove that saturation diving techniques in an underwater laboratory, breathing a nitrogen-oxygen atmosphere could be safely and efficiently accomplished at a minimal cost. Lambertsen's "Predictive Studies Series" that started with Tektite I in 1969 and ended in 1997, researched many aspects of human physiology in extreme environments. When Tektite II ended, General Electric placed

8004-535: The physical environment ( pressure , temperature , light , humidity ), the chemical environment ( drinking water , food , waste products , toxins ) and the biological environment (hazardous sea creatures, microorganisms , marine fungi ). Much of the science covering underwater habitats and their technology designed to meet human requirements is shared with diving , diving bells , submersible vehicles and submarines , and spacecraft . Numerous underwater habitats have been designed, built and used around

8142-554: The 1960s to prove the viability of saturation diving and humans living in isolation for extended periods of time. The knowledge gained from the SEALAB expeditions helped advance the science of deep sea diving and rescue, and contributed to the understanding of the psychological and physiological strains humans can endure. The three SEALABs were part of the United States Navy Genesis Project. Preliminary research work

8280-463: The 80-minute tissue. The atmospheric pressure decreases with altitude, and this has an effect on the absolute pressure of the diving environment. The most important effect is that the diver must decompress to a lower surface pressure, and this requires longer decompression for the same dive profile. A second effect is that a diver ascending to altitude, will be decompressing en route, and will have residual nitrogen until all tissues have equilibrated to

8418-553: The Baltic Sea lasted 11 days. In June 1969, a one-week flat-water mission took place in Lake Constance. In attempting to anchor the habitat at 47 m, the structure was flooded with the two divers in it and sank to the seabed. It was decided to lift it with the two divers according to the necessary decompression profile and nobody was harmed. BAH I provided valuable experience for the much larger underwater laboratory Helgoland. In 2003 it

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8556-626: The United States Navy were terminated. Internationally, except for the La Chalupa Research Laboratory the large-scale projects were carried out, but not extended, so that the subsequent habitats were smaller and designed for shallower depths. The race for greater depths, longer missions and technical advances seemed to have come to an end. For reasons such as lack of mobility, lack of self-sufficiency, shifting focus to space travel and transition to surface-based saturation systems,

8694-558: The University of New Hampshire and NOAA used nitrox as a breathing gas. In the three FLARE missions, the habitat was positioned off Miami at a depth of 13.7 m. The conversion to this experiment increased the weight of the habitat to 23 tonnes. BAH I (for Biological Institute Helgoland ) had a length of 6 m and a diameter of 2 m. It weighed about 20 tons and was intended for a crew of two people. The first mission in September 1968 with Jürgen Dorschel and Gerhard Lauckner at 10 m depth in

8832-461: The accumulated nitrogen from previous dives. Within the Haldanian logic of the model, at least three compartments are off gassing at the prescribed depth - the 5 and 10-minute half time compartments under a relatively high pressure gradient. Therefore, for decompression dives, the existing obligation is not increased during the stop. A PDIS is not a mandatory stop, nor is it considered a substitute for

8970-410: The ascent is interrupted by stops at regular depth intervals, but the entire ascent is part of the decompression, and ascent rate can be critical to harmless elimination of inert gas. What is commonly known as no-decompression diving, or more accurately no-stop decompression, relies on limiting ascent rate for avoidance of excessive bubble formation. Staged decompression may include deep stops depending on

9108-403: The ascent occasionally to get back on schedule, but these stops are not part of the schedule, they are corrections. For example, USN treatment table 5 , referring to treatment in a decompression chamber for type 1 decompression sickness, states "Descent rate - 20 ft/min. Ascent rate - Not to exceed 1 ft/min. Do not compensate for slower ascent rates. Compensate for faster rates by halting

9246-522: The ascent." To further complicate the practice, the ascent rate may vary with the depth, and is typically faster at greater depth and reduces as the depth gets shallower. In practice a continuous decompression profile may be approximated by ascent in steps as small as the chamber pressure gauge will resolve, and timed to follow the theoretical profile as closely as conveniently practicable. For example, USN treatment table 7 (which may be used if decompression sickness has reoccurred during initial treatment in

9384-400: The blood and tissues of the diver if the partial pressures of the dissolved gases in the diver gets too high above the ambient pressure . These bubbles and products of injury caused by the bubbles can cause damage to tissues known as decompression sickness , or "the bends". The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of

9522-428: The body tissues sufficiently to avoid decompression sickness . The practice of making decompression stops is called staged decompression , as opposed to continuous decompression . The diver or diving supervisor identifies the requirement for decompression stops, and if they are needed, the depths and durations of the stops, by using decompression tables , software planning tools or a dive computer . The ascent

9660-458: The bottom time for the tables to remain safe. The ascent is an important part of the process of decompression, as this is the time when reduction of ambient pressure occurs, and it is of critical importance to safe decompression that the ascent rate is compatible with safe elimination of inert gas from the diver's tissues. Ascent rate must be limited to prevent supersaturation of tissues to the extent that unacceptable bubble development occurs. This

9798-400: The case of real-time monitoring by dive computer, descent rate is not specified, as the consequences are automatically accounted for by the programmed algorithm. Bottom time is the time spent at depth before starting the ascent. Bottom time used for decompression planning may be defined differently depending on the tables or algorithm used. It may include descent time, but not in all cases. It

9936-459: The compression chamber) states "Decompress with stops every 2 feet for times shown in profile below." The profile shows an ascent rate of 2 fsw (feet of sea water) every 40 min from 60 fsw to 40 fsw, followed by 2 ft every hour from 40 fsw to 20 fsw and 2 ft every two hours from 20 fsw to 4 fsw. Decompression which follows the procedure of relatively fast ascent interrupted by periods at constant depth

10074-478: The computer fails. This can be a backup computer, a written schedule with watch and depth gauge, or the dive buddy's computer if they have a reasonably similar dive profile. If only no-stop diving is done, and the diver makes sure that the no-stop limit is not exceeded, a computer failure can be managed at acceptable risk by starting an immediate direct ascent to the surface at an appropriate ascent rate. A "no-stop dive", also commonly but inaccurately referred to as

10212-410: The currently published decompression algorithms. More recently computer algorithms that are claimed to use deep stops have become available, but these algorithms and the practice of deep stops have not been adequately validated. Deep stops are likely to be made at depths where ingassing continues for some slow tissues, so the addition of deep stops of any kind can only be included in the dive profile when

10350-406: The decompression calculation switches from on gassing to off gassing and below the depth of the first obligatory decompression stop, (or the surface, on a no-stop dive). The ambient pressure at that depth is low enough to ensure that the tissues are mostly off gassing inert gas, although under a very small pressure gradient. This combination is expected to inhibit bubble growth. The leading compartment

10488-467: The decompression schedule has been computed to include them, so that such ingassing of slower tissues can be taken into account. Nevertheless, deep stops may be added on a dive that relies on a personal dive computer (PDC) with real-time computation, as the PDC will track the effect of the stop on its decompression schedule. Deep stops are otherwise similar to any other staged decompression, but are unlikely to use

10626-400: The decompression then further decompression should be omitted. A bend can usually be treated, whereas drowning, cardiac arrest, or bleeding out in the water is likely to be terminal. A further complication arises when the buddy must decide whether they will also truncate decompression and put themself at risk in the interests of helping the diver in difficulty. In these situations the actual risk

10764-424: The diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during this reduction in pressure. When a diver descends in the water column the ambient pressure rises. Breathing gas is supplied at the same pressure as the surrounding water, and some of this gas dissolves into

10902-483: The diver from their activity. The instrument does not record a depth profile, and requires intermittent action by the panel operator to measure and record the current depth. Elapsed dive time and bottom time are easily monitored using a stopwatch. Worksheets for monitoring the dive profile are available, and include space for listing the ascent profile including decompression stop depths, time of arrival, and stop time. If repetitive dives are involved, residual nitrogen status

11040-402: The diver has a secure breathing gas supply. US Navy tables (Revision 6) start in-water oxygen decompression at 30 fsw (9 msw), equivalent to a partial pressure of 1.9 bar, and chamber oxygen decompression at 50 fsw (15 msw), equivalent to 2.5 bar. Any dive which is started while the tissues retain residual inert gas in excess of the surface equilibrium condition is considered

11178-411: The diver must be known before starting the ascent, so that an appropriate decompression schedule can be followed to avoid an excessive risk of decompression sickness. Scuba divers are responsible for monitoring their own decompression status, as they are the only ones to have access to the necessary information. Surface supplied divers depth profile and elapsed time can be monitored by the surface team, and

11316-518: The diver's blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver's lungs , (see: " Saturation diving "), or the diver moves up in the water column and reduces the ambient pressure of the breathing gas until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again. Dissolved inert gases such as nitrogen or helium can form bubbles in

11454-512: The diver, and the long-term goal is to also avoid complications due to sub-clinical decompression injury. A diver who exceeds the no-decompression limit for a decompression algorithm or table has a theoretical tissue gas loading which is considered likely to cause symptomatic bubble formation unless the ascent follows a decompression schedule, and is said to have a decompression obligation. The descent, bottom time and ascent are sectors common to all dives and hyperbaric exposures. Descent rate

11592-475: The duration of stops the diver is willing to carry out. A procedure for dealing with omitted decompression stops is described in the US Navy Diving Manual. In principle the procedure allows a diver who is not yet presenting symptoms of decompression sickness, to go back down and complete the omitted decompression, with some extra time added to deal with the bubbles which are assumed to have formed during

11730-637: The effect of deep stops observed a significant decrease in vascular bubbles following a deep stop after longer shallower dives, and an increase in bubble formation after the deep stop on shorter deeper dives, which is not predicted by the existing bubble model. A controlled comparative study by the Navy Experimental Diving Unit in the NEDU Ocean Simulation Facility wet-pot comparing the VVAL18 Thalmann Algorithm with

11868-447: The excursion, and downwards by decompression obligations while returning from the excursion. Open circuit or rebreather scuba have the advantage of mobility, but it is critical to the safety of a saturation diver to be able to get back to the habitat, as surfacing directly from saturation is likely to cause severe and probably fatal decompression sickness. For this reason, in most of the programs, signs and guidelines are installed around

12006-429: The first all-female aquanaut team, led by Dr. Sylvia Earle . Other scientists participating in the all-female mission included Dr. Renate True of Tulane University , as well as Ann Hartline and Alina Szmant, graduate students at Scripps Institute of Oceanography. The fifth member of the crew was Margaret Ann Lucas, a Villanova University engineering graduate, who served as Habitat Engineer. The Tektite II missions were

12144-487: The first stop, between stops, and from the last stop to the surface are traditionally known as " pulls ", probably because the ascent was originally controlled by the diver's tender pulling the diver up by the lifeline, and stopping the ascent at the depths planned for staged decompression. Once on the surface, the diver will continue to eliminate inert gas until the concentrations have returned to normal surface saturation, which can take several hours. Inert gas elimination

12282-443: The first to breathe heliox , a mixture of helium and oxygen, avoiding the normal nitrogen /oxygen mixture, which, when breathed under pressure, can cause narcosis . The deep cabin was also an early effort in saturation diving , in which the aquanauts' body tissues were allowed to become totally saturated by the helium in the breathing mixture, a result of breathing the gases under pressure. The necessary decompression from saturation

12420-455: The first to undertake in-depth ecological studies. Tektite II included 24 hour behavioral and mission observations of each of the missions by a team of observers from the University of Texas at Austin . Selected episodic events and discussions were videotaped using cameras in the public areas of the habitat. Data about the status, location and activities of each of the 5 members of each mission

12558-412: The habitat are also limited and depend on the depth of the habitat and the associated saturation of the divers. The open space available for exits thus describes the shape of a vertical axis cylinder centred on the habitat. As an example, in the Tektite I program, the habitat was located at a depth of 13.1 metres (43 ft). Exits were limited vertically to a depth of 6.7 metres (22 ft) (6.4 m above

12696-399: The habitat in order to prevent divers from getting lost. Umbilicals or airline hoses are safer, as the breathing gas supply is unlimited, and the hose is a guideline back to the habitat, but they restrict freedom of movement and can become tangled. The horizontal extent of excursions is limited to the scuba air supply or the length of the umbilical. The distance above and below the level of

12834-672: The habitat in storage in Philadelphia . A group of interested parties purchased the habitat from General Electric for $ 1.00 with the stipulation it would be removed from the GE storage facility. The habitat was trucked across the United States to Fort Mason in San Francisco , where it was placed on display. Attempts were made to refurbish the habitat so it could be used in San Francisco Bay as

12972-455: The habitat) and 25.9 metres (85 ft) (12.8 m below the habitat level) and were horizontally limited to a distance of 549 metres (1,801 ft) from the Habitat. The history of underwater habitats follows on from the previous development of diving bells and caissons , and as long exposure to a hyperbaric environment results in saturation of the body tissues with the ambient inert gases, it

13110-530: The interest in underwater habitats decreased, resulting in a noticeable decrease in major projects after 1970. In the mid eighties, the Aquarius habitat was built in the style of Sealab and Helgoland and is still in operation today. The first aquanaut was Robert Stenuit in the Man-in-the-Sea I project run by Edwin A. Link. On 6 September 1962, he spent 24 hours and 15 minutes at a depth of 61 metres (200 ft) in

13248-550: The laboratory, returning to it after every diving session. At the end of their stay they decompressed in the UWL, and could resurface without decompression sickness. The UWL was used in the waters of the North and Baltic Seas and, in 1975, on Jeffreys Ledge , in the Gulf of Maine off the coast of New England in the United States. At the end of the 1970s it was decommissioned and in 1998 donated to

13386-409: The local pressures. This means that the diver should consider any dive done before equilibration as a repetitive dive, even if it is the first dive in several days. The US Navy diving manual provides repetitive group designations for listed altitude changes. These will change over time with the surface interval according to the relevant table. Altitude corrections (Cross corrections) are described in

13524-412: The mode of diving, the available equipment , the site and environment, and the actual dive profile . Standardized procedures have been developed which provide an acceptable level of risk in the circumstances for which they are appropriate. Different sets of procedures are used by commercial , military , scientific and recreational divers, though there is considerable overlap where similar equipment

13662-422: The more important shallow safety stop on a no-stop dive. Switching breathing gas mix during the ascent will influence the depth of the stop. The PDIS concept was introduced by Sergio Angelini. A decompression schedule is a specified ascent rate and series of increasingly shallower decompression stops—usually for increasing amounts of time—that a diver performs to outgas inert gases from their body during ascent to

13800-407: The obligatory decompression on staged dives. Many dive computers indicate a recommended safety stop as standard procedure for dives beyond specific limits of depth and time. The Goldman decompression model predicts a significant risk reduction following a safety stop on a low-risk dive A safety stop can significantly reduce decompression stress as indicated by venous gas emboli, but if remaining in

13938-484: The ocean floor to begin the ambitious diving project dubbed "Tektite I". By 18 March 1969, the four aquanauts had established a new world's record for saturated diving by a single team. On April 15, 1969, the aquanaut team returned to the surface with over 58 days of marine scientific studies. More than 19 hours of decompression time were needed to accommodate the scientists' return to the surface. The United States Office of Naval Research coordinated Tektite I. Much of

14076-466: The period where the decompression ceiling was violated. Divers who become symptomatic before they can be returned to depth are treated for decompression sickness, and do not attempt the omitted decompression procedure as the risk is considered unacceptable under normal operational circumstances. If a decompression chamber is available, omitted decompression may be managed by chamber recompression to an appropriate pressure, and decompression following either

14214-422: The planned depth of the repetitive dive, a bottom time can be calculated using the relevant algorithm which will provide an equivalent gas loading to the residual gas after the surface interval. This is called "residual nitrogen time" (RNT) when the gas is nitrogen. The RNT is added to the planned "actual bottom time" (ABT) to give an equivalent "total bottom time" (TBT), also called "total nitrogen time" (TNT), which

14352-411: The previous dive and the altitude of the dive site. The diver obtains the depth and duration of each stop from a dive computer , decompression tables or dive planning computer software. A technical scuba diver will typically prepare more than one decompression schedule to plan for contingencies such as going deeper than planned or spending longer at depth than planned. Recreational divers often rely on

14490-659: The project. After Bentos-300 sank in the Russian Black Sea port of Novorossiisk in 1992, several attempts to recover it failed. In November 2011 it was cut up and recovered for scrap in the following six months. The Italian Progetto Abissi habitat, also known as La Casa in Fondo al Mare (Italian for The House at the Bottom of the Sea), was designed by the diving team Explorer Team Pellicano, consisted of three cylindrical chambers and served as

14628-401: The release of excess inert gases dissolved in their body tissues, which accumulated as a result of breathing at ambient pressures greater than surface atmospheric pressure. Decompression models take into account variables such as depth and time of dive, breathing gasses , altitude, and equipment to develop appropriate procedures for safe ascent. Decompression may be continuous or staged, where

14766-411: The research for Tektite I centered on humans in this new environment. Topics investigated would include: biology (blood changes, sleep patterns, oxygen toxicity ), decompression and decompression sickness , microbiology and mycology . The United States Department of the Interior coordinated Tektite II, with part of the funding coming from NASA , which was interested in the psychological study of

14904-404: The responsibility for keeping track of the diver's decompression status is generally part of the supervisor's job. The supervisor will generally assess decompression status based on dive tables, maximum depth and elapsed bottom time of the dive, though multi-level calculations are possible. Depth is measured at the gas panel by pneumofathometer , which can be done at any time without distracting

15042-477: The risk of decompression sickness. Typically maximum ascent rates are in the order of 10 metres (33 ft) per minute for dives deeper than 6 metres (20 ft). Some dive computers have variable maximum ascent rates, depending on depth. Ascent rates slower than the recommended standard for the algorithm will generally be treated by a computer as part of a multilevel dive profile and the decompression requirement adjusted accordingly. Faster ascent rates will elicit

15180-479: The same way, and can use those to either select from a previously compiled set of surfacing schedules, or identify the recommended profile from a waterproof dive table taken along on the dive. It is possible to calculate a decompression schedule for a multilevel dive using this system, but the possibility of error is significant due to the skill and attention required, and the table format, which can be misread under task loading or in poor visibility. The current trend

15318-416: The scientific teams working in closed and restricted environments, similar to that of spacecraft on long missions. A team of Behavioral Observers from the University of Texas at Austin , led by Robert Helmreich, were tasked to record round the clock activities of the aquanauts by CCTV . The missions were carried out in the spring and summer of 1970 in Great Lameshur Bay, Saint John, U.S. Virgin Islands , at

15456-427: The spinal cord and consider that an additional deep safety stop may reduce the risk of spinal cord decompression sickness in recreational diving. A follow-up study found that the optimum duration for the deep safety stop under the experimental conditions was 2.5 minutes, with a shallow safety stop of 3 to 5 minutes. Longer safety stops at either depth did not further reduce PDDB. In contrast, experimental work comparing

15594-493: The study and preservation of marine ecosystems worldwide and is enhancing the scope and impact of FIU on research, educational outreach, technology development, and professional training. At the heart of the program is the Aquarius Reef Base. Dive tables To prevent or minimize decompression sickness , divers must properly plan and monitor decompression . Divers follow a decompression model to safely allow

15732-403: The surface to reduce the risk of decompression sickness . In a decompression dive, the decompression phase may make up a large part of the time spent underwater (in many cases it is longer than the actual time spent at depth). The depth and duration of each stop is dependent on many factors, primarily the profile of depth and time of the dive, but also the breathing gas mix, the interval since

15870-452: The surface, and risks associated with diving and ship operations at night can be minimized. In the habitat La Chalupa , 35% of all dives took place at night. To perform the same amount of useful work diving from the surface instead of from La Chalupa , an estimated eight hours of decompression time would have been necessary every day. However, maintaining an underwater habitat is much more expensive and logistically difficult than diving from

16008-473: The surface. It also restricts the diving to a much more limited area. Underwater habitats are designed to operate in two fundamental modes. A third or composite type has compartments of both types within the same habitat structure and connected via airlocks, such as Aquarius . An excursion is a visit to the environment outside the habitat. Diving excursions can be done on scuba or umbilical supply, and are limited upwards by decompression obligations while on

16146-420: The table will specify how the schedule should be adjusted to compensate for delays during the ascent. Typically a delay in reaching the first stop is added to bottom time, as ingassing of some tissues is assumed, and delays between scheduled stops are ignored, as it is assumed that no further ingassing has occurred. This may be considered a special case of a multi-level dive . Decompression can be accelerated by

16284-627: The theoretical model used for calculating the ascent schedule. Omission of decompression theoretically required for a dive profile exposes the diver to significantly higher risk of symptomatic decompression sickness, and in severe cases, serious injury or death. The risk is related to the severity of exposure and the level of supersaturation of tissues in the diver. Procedures for emergency management of omitted decompression and symptomatic decompression sickness have been published. These procedures are generally effective, but vary in effectiveness from case to case. The procedures used for decompression depend on

16422-532: The tissue model and recent diving history of the user). Residual inert gas can be computed for all modeled tissues, but repetitive group designations in decompression tables are generally based on only the one tissue, considered by the table designers to be the most limiting tissue for likely applications. In the case of the US Navy Air Tables (1956) this is the 120-minute tissue, while the Bühlmann tables use

16560-416: The total tissue tension of inert gases in a tissue to exceed the ambient pressure sufficiently to cause bubble formation, even if the ambient pressure has not been reduced at the time of the gas switch. They conclude that "breathing-gas switches should be scheduled deep or shallow to avoid the period of maximum supersaturation resulting from decompression". The use of pure oxygen for accelerated decompression

16698-567: The underwater Habitat Engineer on the International Mission, the last mission on the Tektite II project. The Program Manager for the Tektite projects was Dr. Theodore Marton at General Electric. The habitat appeared as a pair of silos: two white metal cylinders 12.5 feet (3.8 m) in diameter and 18 feet (5.5 m) high, joined by a flexible tunnel and seated on a rectangular base in 43 feet (13 m) depth of water. On 28 January 1969,

16836-418: The use of breathing gases during ascent with lowered inert gas fractions (as a result of increased oxygen fraction). This will result in a greater diffusion gradient for a given ambient pressure, and consequently accelerated decompression for a relatively low risk of bubble formation. Nitrox mixtures and oxygen are the most commonly used gases for this purpose, but oxygen rich trimix blends can also be used after

16974-427: The water to do a safety stop increases risk due to another hazard, such as running out of gas underwater or a significant medical emergency then the overall safety of the diver may be best served by omitting the safety stop. A similar balancing of hazard and risk also applies to surfacing with omitted decompression, or bringing an unresponsive, non-breathing, diver to the surface. If the risk appears greater for completing

17112-524: The world since as early as the start of the 1960s, either by private individuals or by government agencies. They have been used almost exclusively for research and exploration , but, in recent years, at least one underwater habitat has been provided for recreation and tourism . Research has been devoted particularly to the physiological processes and limits of breathing gases under pressure, for aquanaut , as well as astronaut training, and for research on marine ecosystems. The term 'underwater habitat'

17250-452: The world's most extensively used habitat. MarineLab was used as an integral part of the "Scott Carpenter, Man in the Sea" Program. In 2018 the habitat was retired and restored to its 1985 condition and is on display to the public at Marine Resources Development Foundation, Inc. Key Largo, Florida. The Aquarius Reef Base is an underwater habitat located 5.4 miles (9 kilometers) off Key Largo in

17388-627: Was Dr. Theodore Marton. Hydrolab was constructed in 1966 at a cost of $ 60,000 ($ 560,000 in today's currency) and used as a research station from 1970. The project was in part funded by the National Oceanic and Atmospheric Administration (NOAA). Hydrolab could house four people. Approximately 180 Hydrolab missions were conducted—100 missions in The Bahamas during the early to mid-1970s, and 80 missions off Saint Croix, U.S. Virgin Islands , from 1977 to 1985. These scientific missions are chronicled in

17526-400: Was a defining effort in the study of diving physiology and technology, and captured wide public appeal due to its dramatic " Jules Verne " look and feel. A Cousteau-produced feature film about the effort ( World Without Sun ) was awarded an Academy Award for Best Documentary the following year. Conshelf III was initiated in 1965. Six divers lived in the habitat at 102.4 metres (336 ft) in

17664-611: Was a horizontal cylinder 2.6 m high, 3.3 m long and weighing 14 tonnes was built by students of the Engineering Design and Analysis Laboratory in the US at a cost of $ 20,000 or $ 187,000 in today's currency. From 26 April 1968, four students spent 48 hours and 6 minutes in this habitat in Alton Bay, New Hampshire. Two further missions followed to 12.2 m. In the 1972 Edalhab II Florida Aquanaut Research Expedition experiments,

17802-406: Was accelerated by using oxygen enriched breathing gases. They suffered no apparent ill effects. The undersea colony was supported with air, water, food, power, all essentials of life, from a large support team above. Men on the bottom performed a number of experiments intended to determine the practicality of working on the sea floor and were subjected to continual medical examinations. Conshelf II

17940-455: Was an inflatable structure called SPID. This was followed by a series of underwater habitats where people stayed for several weeks at great depths. Sealab II had a usable area of 63 square metres (680 sq ft), and was used at a depth of more than 60 metres (200 ft). Several countries built their own habitats at much the same time and mostly began experimenting in shallow waters. In Conshelf III six aquanauts lived for several weeks at

18078-436: Was collected via key punch data cards every six minutes during each mission. This information was collated and processed by BellComm and was used for the support of papers written about the research concerning the relative predictability of behavior patterns of mission participants in constrained, dangerous conditions for extended periods of time, such as those that might be encountered in crewed spaceflight. The Tektite habitat

18216-549: Was designed and built by General Electric Space Division at the Valley Forge Space Technology Center in King of Prussia, Pennsylvania . The Project Engineer who was responsible for the design of the habitat was Brooks Tenney, Jr. Tenney also served as the underwater Habitat Engineer on the International Mission, the last mission on the Tektite II project. The Program Manager for the Tektite projects at General Electric

18354-471: Was for five of these stations to be submerged to a maximum depth of 300 metres (1,000 ft) over the decade; in reality only three were completed with a maximum depth of 100 metres (330 ft). Much of the work was funded in part by the French petrochemical industry , who, along with Cousteau, hoped that such colonies could serve as base stations for the future exploitation of the sea. Such colonies did not find

18492-592: Was owned by the National Oceanic and Atmospheric Administration (NOAA) and operated by the University of North Carolina–Wilmington until 2013 when Florida International University assumed operational control. Florida International University (FIU) took ownership of Aquarius in October 2014. As part of the FIU Marine Education and Research Initiative, the Medina Aquarius Program is dedicated to

18630-414: Was restored to be functional, but never used underwater again. Instead, it was open to visitors on dry land in San Francisco . The Tektite habitat was designed and built by General Electric Company Space Division at the Valley Forge Space Technology Center in King of Prussia, Pennsylvania . The Project Engineer who was responsible for the design of the habitat was Brooks Tenney, Jr. Tenney also served as

18768-732: Was taken over as a technical monument by the Technical University of Clausthal-Zellerfeld and in the same year went on display at the Nautineum Stralsund on Kleiner Dänholm island. The Helgoland underwater laboratory (UWL) is an underwater habitat. It was built in Lübeck , Germany in 1968, and was the first of its kind in the world built for use in colder waters. The 14 meter long, 7 meter diameter UWL allowed divers to spend several weeks under water using saturation diving techniques. The scientists and technicians would live and work in

18906-562: Was the first saturation diving project to employ scientists rather than professional divers. The term tektite generally refers to a class of meteorites formed by extremely rapid cooling. These include objects of celestial origins that strike the sea surface and come to rest on the bottom (note project Tektite's conceptual origins within the U.S space program). The Tektite II missions were carried out in 1970. Tektite II comprised ten missions lasting 10 to 20 days with four scientists and an engineer on each mission. One of these missions included

19044-402: Was undertaken by George F. Bond . Bond began investigations in 1957 to develop theories about saturation diving . Bond's team exposed rats , goats , monkeys , and human beings to various gas mixtures at different pressures. By 1963 they had collected enough data to test the first SEALAB habitat. The Tektite underwater habitat was constructed by General Electric and was funded by NASA ,

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