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Wireless Robot discovers three chamber in Teotihuacan

Wireless Robot discovers three chamber in Teotihuacan

Archaeologists in Mexico with the help of a wireless robot named Tlaloc II-TC, have discovered three chambers under the temple of the Feathered Serpent (Quetzalcoatl). Although initially the archaeologists expected to find one chamber, to their surprise they found three.

The robot cleared the way to the chambers through a tunnel of 30 to 35 meters. Tlaloc which is equipped with a camera and robotic arms, managed to take a series of pictures identifying the chambers. According to team leader Sergio Gomez, the chambers may have been used by the rulers of Teotihuacan about 2,000 years ago either for ceremonies of as burial places.

Similar chambers were found under the Pyramid of the Sun that were explored in the 70s and as Sergio says a similar configuration seems to exist in the temple of Quetzalcoatl too. More research is needed to be done and the chamber to be cleared for further exploration.

Teotihuacan is one of the largest and most important sacred cities of ancient Mesoamerica. Its name means the ‘place where the gods were born’ and according to the Aztecs it is the place where the ‘Gods’ created the Universe. Although through carbon dating of organic material in the area it is dated to 300 AD, legends and myths as well as alternative archaeologists date the temple many thousands of years before. A popular theory is that it wasn’t even built by the Aztec but it was only used by the Aztecs who found it there (similar assumptions exist for the Pyramids and other monuments). As a result, very little is known about who the builders were, what the purpose of the temple was and what the religious beliefs of the people who used it were.

    The History Blog

    The excavations under the Temple of the Feathered Serpent in Teotihuacan have unearthed another exceptional find: large quantities of liquid mercury. Archaeologist Sergio Gómez and his team have been excavating the tunnel underneath the pre-Aztec pyramid, discovered by accident in 2003 when a sinkhole opened up in front of the temple, since 2009, using a robot to reveal three chambers at the end of the tunnel and last year discovering an enormous cache of 50,000 artifacts (sculptures, jade, rubber balls, obsidian blades, pyrite mirrors) and organic remains (animal bones, fur, plants, seeds, skin). It has taken so long to excavate it because the tunnel was filled to the brim with soil and rocks and sealed 1,800 years ago by the people of Teotihuacan about whom we know very little.

    The mercury was found in one of the chambers discovered by the robot at the end of the tunnel.

    “It’s something that completely surprised us,” Gomez said at the entrance to the tunnel below Teotihuacan’s Pyramid of the Plumed Serpent, about 30 miles (50 km) northeast of Mexico City.

    Some archeologists believe the toxic element could herald what would be the first ruler’s tomb ever found in Teotihuacan, a contemporary of several ancient Maya cities, but so shrouded in mystery that its inhabitants still have no name.

    Unsure why the mercury was put there, Gomez says the metal may have been used to symbolize an underworld river or lake.

    />Mercuric sulfide is the most commonly found source of mercury ore and ancient Mesoamericans were intimately familiar with it both as a red pigment and for its mercury content. They knew how to extract mercury from crushed cinnabar — heating the ore separates the mercury from sulfur and the evaporated mercury can then be collected in a condensing column — and employed it as a gilding medium and possibly for ritual purposes. It was very difficult and dangerous to produce. Before now, traces of mercury have only been found at a two Maya sites and one Olmec site in Central America. This is the first time it has been discovered in Teotihuacan, and I suspect this is the first time it has been discovered in large amounts anywhere in ancient Mexico. (The exact quantities discovered under the Temple of the Feathered Serpent and at the other sites haven’t been reported.)

    Reflective materials held a great deal of religious significance in Mesoamerican cultures. Mirrors were seen as conduits to the supernatural. A river of mercury would make one hugely expensive and ritually important conveyance to the underworld. Added to the exceptional finds already made in the tunnel, the presence of so much mercury indicates that if anybody was buried in these chambers, it would have to be someone of enormous importance in Teotihuacan society. It could be a king, but we don’t know what kind of governing system they had in Teotihuacan, so it could be a lord, several oligarchs or religious leaders. The hope is that this excavation and its unprecedented finds will answer many of the long-outstanding questions about the city of Teotihuacan.

    I’m excited about this discovery because I’ve been fascinated by the notion of underground rivers of mercury since I first read about the ones reportedly created for the tomb of the first Emperor of China Qin Shi Huang. Better known today for the terracotta army found in pits around the emperor’s burial mound, the mausoleum itself was apparently a thing of shimmering splendour. Grand Historian to the Han emperor Sima Qian, writing a century after the Qin emperor’s death, described Qin Shi Huang’s mausoleum in Volume Six of the Shiji (Records of the Grand Historian), China’s first official dynastic history.

    They dug down deep to underground springs, pouring copper to place the outer casing of the coffin. Palaces and viewing towers housing a hundred officials were built and filled with treasures and rare artifacts. Workmen were instructed to make automatic crossbows primed to shoot at intruders. Mercury was used to simulate the hundred rivers, the Yangtze and Yellow River, and the great sea, and set to flow mechanically. Above, the heaven is depicted, below, the geographical features of the land.

    As the emperor’s burial mound has not been excavated (just the environs), we don’t know if the rivers of flowing mercury really existed, but high levels of mercury have been found in soil samples taken from the tumulus so significant amounts of the heavy metal were certainly used for some purpose. I think it would be the coolest thing if the people of Teotihuacan created their own shimmering splendor of an underworld too.

    This entry was posted on Saturday, April 25th, 2015 at 2:37 PM and is filed under Ancient. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

    The History Blog

    />A robot named Tláloc II-TC, equipped with an infrared camera and laser scanner, has discovered three new chambers underneath the Temple of the Feathered Serpent pyramid in the Mesoamerican metropolis of Teotihuacan. He was sent down a tunnel 390 feet long that was discovered 50 feet below the surface of the temple in 2003. The tunnel had been filled with debris by the ancient Teotihuacans to block access, an effective technique since despite centuries of looting and archaeological excavations nobody had managed to breach it. It’s been a decade since the subterranean conduit was discovered and five years since excavations began, and archaeologists have only able to get a glimpse of what’s on the other side in the past few months.

    />They first discovered two side rooms dubbed the North Chamber and the South Chamber 236 and 242 feet respectively from the entrance. The human archaeologists couldn’t get any further than that, so they deployed Tláloc II-TC to travel another 65 feet. The terrain was uncongenial, to say the least, with the floor in some parts of the tunnel caked in sludge a foot deep. Tláloc is neither light as a feather nor stiff as a board. He weighs 77 pounds and his articulated tank-track feet kept getting stuck in the thick mud. Archaeologists believe the Teotihuacans intentionally dug down to the water table in order to build a space that recreated the conditions of the underworld.

    Despite the navigation difficulties, Tláloc’s sensors never failed. They revealed that the tunnel has a semicircular vault and is a constant size and shape until it reaches the entryways of three previously unknown chambers. The rooms are blocked by a wall or large stone so Tláloc wasn’t able to go inside, but his scanner detected spaces that are deeper than 16 feet. The scanner can only record a maximum of five meters (approximately 16 feet) in depth. It can detect that there’s more than that to be found only it can’t find out exactly how much until it’s inside the chambers.

    />They’ll need to clean out the tunnel to make it accessible to puny humans before they can reach the chambers Tláloc has found. The team hopes these rooms, hidden deep underground and deliberately made so unreachable not even highly motivated thieves and archaeologists were able to explore them for almost 2000 years after they were closed, might contain something of inestimable significance to Teotihuacan society, perhaps even the graves of the city’s founders.

    />Meanwhile, archaeologists exploring North Chamber and South Chamber have discovered some unusual artifacts. They look like yellowish clay lumps ranging in diameter from 1.5 to five inches, but they’re man-made with a core of clay covered in iron pyrite. When new, they would have been spherical and the pyrite exterior, which has oxidized into duller jarosite, would have been shiny gold. The adobe walls of the chambers were also enhanced for shininess. They were coated with a powder compound of magnetite, pyrite and hematite which would have made this dark underground space gleam.

    The lumps/spheres must have been left in the space before the tunnel was closed 1800 years ago. What function they may have played is unknown at this juncture, but the prevailing hypothesis is that they were special ritual offerings of some kind. No other such artifacts have been discovered before, but many other offerings — pottery, wooden masks inlaid with rock crystal and jade — were also found in the chambers so it seems likely the balls had the same job. The pottery and masks have been dated to around 100 A.D.

    />The Temple of the Feathered Serpent, also known as the Temple of Quetzalcoatl after the feathered serpent deity of the Aztecs who moved in to the city in the 14th century A.D. long after the original Teotihuacans had mysteriously abandoned it in the 8th century, is the third largest of Teotihuacan’s temples. The largest is the Pyramid of the Sun under which a similar tunnel was discovered in the 1970s. That excavation was less than scientifically rigorous, however, and much of the precious context information was lost. The clean, deliberate nature of this multi-season exploration, on the other hand, will ensure all of the data that can be retrieved will be retrieved. This will hopefully reveal important new information about the religious life of Teotihuacan.

    This entry was posted on Wednesday, May 1st, 2013 at 3:03 PM and is filed under Ancient. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

    In pictures: Relics discovered in Mexico's Teotihuacan

    The city, located about 50 km (30 miles) northeast of Mexico City, dominated central Mexico in pre-Columbian times.

    The relics found include jewellery, seeds, animal bones and pottery like these human figurines.

    The objects were found inside a sacred tunnel that was sealed about 1,800 years ago.

    The entrance of the tunnel was discovered in 2003 and its contents came to light after the archaeologists worked meticulously for nine years.

    The researchers dug out mountains of dirt and rocks, using remote-control robots, and found zoomorphic vessels like this.

    The artefacts, like these sea shells, were unearthed from about 18 metres (60 feet) below the Temple of the Plumed Serpent, the third largest pyramid at Teotihuacan.

    At the end of the tunnel, the archaeologists also discovered offerings just before three chambers, suggesting that the remains of city's ruling elite could be buried there.

    Such a discovery could help shine light on the leadership structure of Teotihuacan, including whether rule was hereditary.

    The ancient city is the largest pre-Columbian archaeological site in the Americas, but its ruins have long been shrouded in mystery because its inhabitants did not leave behind written records.

    A robot will explore the tunnel under the Temple of the Feathered Serpent in Teotihuacan

    After the recent discovery of a tunnel under the Temple of the Feathered Serpent in Teotihuacan , a robot (the first one used in Mexico for archaeological purposes) is already ready with the intention of exploring and discovering if the hypothesis that they can be found buried there The rulers of Teotihuacan is true or not.

    The first images of the interior of the tunnel were shown today to the press, which marks a milestone in the history of archaeological excavations in Mexico and the Americas. It is the first time in the history of Mexican archeology and the second in the world after Egypt, in which a robot participates in an archaeological investigation.

    Tlaloque I, the name of the robot, traveled the first sections of a tunnel through which no one had traveled for at least 800 thousand years. The images he recorded show stability and make it feasible for researchers to enter the pre-Hispanic conduit, built over two thousand years ago by the ancient Teotihuacans to represent the underworld. Previously with the use of a georradar it was determined with precision that the tunnel leads to three chambers, where eventually the remains of important characters could rest.

    Archaeologist Sergio Gómez Chávez, director of the Tlalocan Project commented that:
    ” The entire duct, more than 100 meters long, is perfectly excavated in the rock, in some parts you can see the marks of the tools with which the Teotihuacans did it, the tunnel roof is domed and at least the part that the robot traveled is stable, which gives us many possibilities that in the coming weeks we can physically enter to explore it. Although the tunnel is filled with earth and stones, the robot was able to travel a few meters through a small space of just 25 centimeters high, which is between the roof and the dusty part. We are calculating that by the end of this month or the beginning of December we will have removed a part of the land that is blocking access and then we can already enter. It was also possible to observe in greater detail the large carved stones inside the tunnel. Apparently it is perfectly carved sculptures or rocks, of great dimensions and weight, which were introduced by the Teotihuacans to close the access between the years 200 and 250 AD, that is, approximately 1,800 years ago.

    About Author

    Hi, my name is Sharon Isaiah Woods, and I work as an assistant professor of History at the California Institute for Regenerative Medicine. I love writing blogs related to History and technology. I have created this blog so that you can easily share your views.

    Teotihuacan: The Ancient Pyramids of a Lost Civilization

    [T]he Pre-Hispanic city of Teotihuacan is a UNESCO World Heritage Site located 30 miles outside of Mexico City.

    Dating back 2,000 years, the city was once thought to support 125,000 people, making it one of the largest urban centers in the world at that time.

    Despite its grandeur, little is known about the civilization that built the pyramids at Teotihuacan.

    By the time the Aztecs discovered the city, it had already been abandoned for hundreds of years.

    Today, modern technology including radar and robots are slowly lifting the veil on the mysterious history of a lost civilization.

    In the late 1980's, a burial pit containing the remains of 200 sacrificed warriors was discovered at the core of the Temple of the Feathered Serpent. As recently as 2011, a robot was used to discover ancient burial chambers, which have been sealed off for as many as 1,800 years. Source Completed around 200 AD, the Pyramid of the Sun is 63 meters tall, with a base 225 meters long on each of the four sides. It is the largest structure in Teotihuacan, and one of the largest of its kind in the Western Hemisphere. The steep climb up the Pyramid of the Sun rewards visitors with sweeping views of Teotihuacan, including the Pyramid of the Moon (seen in the upper right). A straight view toward the Avenue of the Dead, which runs the length of Teotihuacan, from atop the Pyramid of the Sun. People of all ages were climbing the Pyramid of the Sun, from toddlers to older folks. Like me, I believe most felt a lot more comfortable once they were back down again. The Pyramid of the Sun as viewed from the Avenue of the Dead. Walking down the Avenue of the Dead, toward the Pyramid of the Moon. This main street through Teotihuacan runs north/south for approximately two miles. The 46-meter Pyramid of the Moon also contains evidence of human and animal sacrifices. Green bird painted in the Templo de los Caracoles Emplumados (Green Bird Procession). Patio de los Pilares (Patio of Pillars) located in the Quetzalpapalotl Palace, near the Pyramid of the Moon.

    The Pre-Hispanic City of Teotihuacan became a World Heritage Site in 1987.

    Click here for the full list of UNESCO sites Dave has visited during his travels.

    My Mexico Ancient Civilizations tour is in partnership with G Adventures. Any opinions expressed are entirely my own.

    21 Sealed Tunnels - Right Underneath the Temples

    Once the digital map was finished, Gómez and his team found an entrance to the underground tunnel they found beneath the Temple of the Plumed Serpent which seemed to be “Intentionally sealed with large boulders nearly 2,000 years ago” as stated by Forbes. Not long after this discovery, they dug through the entrance and made their way further into the tunnel with help from two robots called Tlaloque (as mentioned earlier) and its matching counterpart Tláloc II. What they uncovered was an entire chamber full of various objects that were “Deposited deliberately and pointedly, as if in offering” Forbes describes.

    Fool’s Gold

    They yellow colour comes from jarosite, which forms as pyrite — or fool’s gold — oxidizes. So back in 300 AD, when the Teotihuacanos used with these variously sized (1.5 to 5 inches) balls in whatever ceremonies or rituals they engaged in, they were looking at what might have seemed like beautiful, glimmering balls of gold.

    As George Gowgill, professor emeritus at Arizona State University told Discovery News:

    Pyrite was certainly used by the Teotihuacanos and other ancient Mesoamerican societies. Originally the spheres would have shown brilliantly. They are indeed unique, but I have no idea what they mean.

    As the walls themselves were also dusted with pyrite — giving a lovely golden sheen to the potter and crystal-covered masks scattered around the room — the archaeologists believe that “high-ranking people, priests, or even rulers went down to the tunnel to perform rituals.”

    Thousands Of Relics Recovered From Ancient Mexican City

    After spending years gradually making their way down a 103 meter (340 foot) long tunnel, a team of Mexican archeologists have gathered some 50,000 relics inside the ancient city of Teotihuacan. The remains, which could offer new insight into the impressive city, have been untouched for almost 2,000 years because the opening was sealed around A.D. 250.

    The pre-Columbian city of Teotihuacan is located around 50 kilometers (30 miles) northeast of Mexico City. It was built between the firstਊnd seventhꃎnturies A.D., and comprises an awe-inspiring spread of temples that are laid out on geometric and symbolic principles. The city’s most impressive building is undoubtedly the Pyramid of the Sun, which is the third largest pyramid in the world. It was reconstructed by archeologists some time ago, but it’s believed they made a mistake and rebuilt this particular structure with the wrong number of levels. Whoops.

    The new discoveries were made when project leader Sergio Gomez and his team worked their way down a previously closed off tunnel that was discovered back in 2003. They dug out piles of dirt and rocks using remote-controlled robots, unearthing a trove of goodies on the way.

    The ancient artifacts discovered include shells, animal bones, jewelry, pottery and seeds. They were located around 18 meters (60 feet) below a building called the Temple of the Plumed Serpent, which is the third largest pyramid at the site.

    They also came across offerings left outside three previously undiscovered chambers, which could suggest that the city’s elite may be buried inside. No remains of Teotihuacan’s leaders have been discovered so far, and inhabitants never left any written records, so finding them could finally provide archeologists with important information on how the city was ruled. But they’ll need to do a lot more digging before they find out, because so far they’ve only gotꁠ centimeters inside the chambers.

    “We have not lost hope of finding that, and if they are there, they must be from someone very, very important,” said Gomez. 


    On December 22, 1938, Edgar End and Max Nohl made the first intentional saturation dive by spending 27 hours breathing air at 101 feet sea water (fsw) (30.8 msw) in the County Emergency Hospital recompression facility in Milwaukee, Wisconsin. Their decompression lasted five hours leaving Nohl with a mild case of decompression sickness that resolved with recompression. [5]

    Albert R. Behnke proposed the idea of exposing humans to increased ambient pressures long enough for the blood and tissues to become saturated with inert gases in 1942. [6] [7] In 1957, George F. Bond began the Genesis project at the Naval Submarine Medical Research Laboratory proving that humans could in fact withstand prolonged exposure to different breathing gases and increased environmental pressures. [6] [8] Once saturation is achieved, the amount of time needed for decompression depends on the depth and gases breathed. This was the beginning of saturation diving and the US Navy's Man-in-the-Sea Program. [9] The first commercial saturation dives were performed in 1965 by Westinghouse to replace faulty trash racks at 200 feet (61 m) on the Smith Mountain Dam. [5]

    Peter B. Bennett is credited with the invention of trimix breathing gas as a method to eliminate high pressure nervous syndrome. In 1981, at the Duke University Medical Center, Bennett conducted an experiment called Atlantis III, which involved subjecting volunteers to a pressure of 2250 fsw (equivalent to a depth of 686 m in seawater), and slowly decompressing them to atmospheric pressure over a period of 31-plus days, setting an early world record for depth-equivalent in the process. A later experiment, Atlantis IV, encountered problems as one of the volunteers experienced euphoric hallucinations and hypomania. [10]

    Saturation diving has applications in scientific diving and commercial offshore diving. [11]

    Commercial offshore diving, sometimes shortened to just offshore diving, is a branch of commercial diving, with divers working in support of the exploration and production sector of the oil and gas industry in places such as the Gulf of Mexico in the United States, the North Sea in the United Kingdom and Norway, and along the coast of Brazil. The work in this area of the industry includes maintenance of oil platforms and the building of underwater structures. In this context "offshore" implies that the diving work is done outside of national boundaries.

    Saturation diving is standard practice for bottom work at many of the deeper offshore sites, and allows more effective use of the diver's time while reducing the risk of decompression sickness. [2] Surface oriented air diving is more usual in shallower water.

    Underwater habitats are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene, and sleeping. In this context 'habitat' is generally used in a narrow sense to mean the interior and immediate exterior of the structure and its fixtures, but not its surrounding marine environment. Most early underwater habitats lacked regenerative systems for air, water, food, electricity, and other resources. However, recently some new underwater habitats allow for these resources to be delivered using pipes, or generated within the habitat, rather than manually delivered. [12]

    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 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 the world since the early 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 and astronaut training, as well as for research on marine ecosystems. Access to and from the exterior is generally vertically through a hole in the bottom of the structure called a moon pool. The habitat may include a decompression chamber, or personnel transfer to the surface may be via a closed diving bell.

    Employment Edit

    Saturation diving work in support of the offshore oil and gas industries is usually contract based. [13]

    Decompression sickness Edit

    Decompression sickness (DCS) is a potentially fatal condition caused by bubbles of inert gas, which can occur in divers' bodies as a consequence of the pressure reduction as they ascend. To prevent decompression sickness, divers have to limit their rate of ascent, to reduce the concentration of dissolved gases in their body sufficiently to avoid bubble formation and growth. This protocol, known as decompression, can last for several hours for dives in excess of 50 metres (160 ft) when divers spend more than a few minutes at these depths. The longer divers remain at depth, the more inert gas is absorbed into their body tissues, and the time required for decompression increases rapidly. [14] This presents a problem for operations that require divers to work for extended periods at depth, as the time spent decompressing can exceed the time spent doing useful work by a large margin. However, after somewhere around 72 hours under any given pressure, depending on the ingassing model used, divers' bodies become saturated with inert gas, and no further uptake occurs. From that point onward, no increase in decompression time is necessary. The practice of saturation diving takes advantage of this by providing a means for divers to remain at depth pressure for days or weeks. At the end of that period, divers need to carry out a single saturation decompression, which is much more efficient and a lower risk than making multiple short dives, each of which requires a lengthy decompression time. By making the single decompression slower and longer, in the controlled conditions and relative comfort of the saturation habitat or decompression chamber, the risk of decompression sickness during the single exposure is further reduced. [2]

    High pressure nervous syndrome Edit

    High pressure nervous syndrome (HPNS) is a neurological and physiological diving disorder that results when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth. [15] HPNS is a limiting factor in future deep diving. [16] HPNS can be reduced by using a small percentage of nitrogen in the gas mixture. [16]

    Compression arthralgia Edit

    Compression arthralgia is a deep aching pain in the joints caused by exposure to high ambient pressure at a relatively high rate of compression, experienced by underwater divers. The pain may occur in the knees, shoulders, fingers, back, hips, neck or ribs, and may be sudden and intense in onset and may be accompanied by a feeling of roughness in the joints. [17] Onset commonly occurs around 60 msw (meters of sea water), and symptoms are variable depending on depth, compression rate and personal susceptibility. Intensity increases with depth and may be aggravated by exercise. Compression arthralgia is generally a problem of deep diving, particularly deep saturation diving, where at sufficient depth even slow compression may produce symptoms. The use of trimix can reduce the symptoms. [18] Spontaneous improvement may occur over time at depth, but this is unpredictable, and pain may persist into decompression. Compression arthralgia may be easily distinguished from decompression sickness as it is starts during descent, is present before starting decompression, and resolves with decreasing pressure, the opposite of decompression sickness. The pain may be sufficiently severe to limit the diver's capacity for work, and may also limit the depth of downward excursions. [17]

    Dysbaric osteonecrosis Edit

    Saturation diving (or more precisely, long term exposure to high pressure) is associated with aseptic bone necrosis, although it is not yet known if all divers are affected or only especially sensitive ones. The joints are most vulnerable to osteonecrosis. The connection between high-pressure exposure, decompression procedure and osteonecrosis is not fully understood. [19] [20] [21]

    Extreme depth effects Edit

    A breathing gas mixture of oxygen, helium and hydrogen was developed for use at extreme depths to reduce the effects of high pressure on the central nervous system. Between 1978 and 1984, a team of divers from Duke University in North Carolina conducted the Atlantis series of on-shore-hyperbaric-chamber-deep-scientific-test-dives. [10] In 1981, during an extreme depth test dive to 686 metres (2251 ft) they breathed the conventional mixture of oxygen and helium with difficulty and suffered trembling and memory lapses. [10] [22]

    A hydrogen–helium–oxygen (hydreliox) gas mixture was used during a similar on shore scientific test dive by three divers involved in an experiment for the French Comex S.A. industrial deep-sea diving company in 1992. On 18 November 1992, Comex decided to stop the experiment at an equivalent of 675 meters of sea water (msw) (2215 fsw) because the divers were suffering from insomnia and fatigue. All three divers wanted to push on but the company decided to decompress the chamber to 650 msw (2133 fsw). On 20 November 1992, Comex diver Theo Mavrostomos was given the go-ahead to continue but spent only two hours at 701 msw (2300 fsw). Comex had planned for the divers to spend four and a half days at this depth and carry out tasks. [22]

    Health effects of living under saturation conditions Edit

    There is some evidence of long term cumulative reduction in lung function in saturation divers. [23]

    Saturation divers are frequently troubled by superficial infections such as skin rashes, otitis externa and athlete's foot, which occur during and after saturation exposures. This is thought to be a consequence of raised partial pressure of oxygen, and relatively high temperatures and humidity in the accommodation. [24]

    Dysbaric osteonecrosis is considered a consequence of decompression injury rather than living under saturation conditions.

    Saturation diving allows professional divers to live and work at pressures greater than 50 msw (160 fsw) for days or weeks at a time, though lower pressures have been used for scientific work from underwater habitats. This type of diving allows for greater economy of work and enhanced safety for the divers. [1] After working in the water, they rest and live in a dry pressurized habitat on or connected to a diving support vessel, oil platform or other floating work station, at approximately the same pressure as the work depth. The diving team is compressed to the working pressure only once, at the beginning of the work period, and decompressed to surface pressure once, after the entire work period of days or weeks. Excursions to greater depths require decompression when returning to storage depth, and excursions to shallower depths are also limited by decompression obligations to avoid decompression sickness during the excursion. [1]

    Increased use of underwater remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) for routine or planned tasks means that saturation dives are becoming less common, though complicated underwater tasks requiring complex manual actions remain the preserve of the deep-sea saturation diver. [ citation needed ]

    A person who operates a saturation diving system is called a Life Support Technician (LST). [25] : 23

    Personnel requirements Edit

    A saturation diving team requires at the minimum the following personnel: [26]

    • A diving supervisor (on duty during any diving operations)
    • Two life-support supervisors (working shifts while there are divers under pressure)
    • Two life-support technicians (also working shifts)
    • Two divers in the bell (working diver and bellman - they may alternate during the dive)
    • One surface stand-by diver (on duty when the bell is in the water)
    • One tender for the surface stand-by diver

    In some jurisdictions there will also be a diving medical practitioner on standby, but not necessarily on site, and some companies may require a diving medical technician on site. The actual personnel actively engaged in aspects of the operation are usually more than the minimum. [26]

    Compression Edit

    Compression to storage depth is generally at a limited rate [27] to minimize the risk of HPNS and compression arthralgia. Norwegian standards specifies a maximum compression rate of 1 msw per minute, and a rest period at storage depth after compression and before diving. [27]

    Storage depth Edit

    Storage depth, also known as living depth, is the pressure in the accommodation sections of the saturation habitat—the ambient pressure under which the saturation divers live when not engaged in lock-out activity. Any change in storage depth involves a compression or a decompression, both of which are stressful to the occupants, and therefore dive planning should minimize the need for changes of living depth and excursion exposures, and storage depth should be as close as practicable to the working depth, taking into account all relevant safety considerations. [27]

    Atmosphere control Edit

    The hyperbaric atmosphere in the accommodation chambers and the bell are controlled to ensure that the risk of long term adverse effects on the divers is acceptably low. Most saturation diving is done on heliox mixtures, with partial pressure of oxygen in accommodation areas kept around 0.40 to 0.48 bar, which is near the upper limit for long term exposure. Carbon dioxide is removed from the chamber gas by recycling it through scrubber cartridges. The levels are generally limited to a maximum of 0.005 bar partial pressure, equivalent to 0.5% surface equivalent. Most of the balance is helium, with a small amount of nitrogen and trace residuals from the air in the system before compression. [1]

    Bell operations and lockouts may also be done at between 0.4 and 0.6 bar oxygen partial pressure, but often use a higher partial pressure of oxygen, between 0.6 and 0.9 bar, [28] which lessens the effect of pressure variation due to excursions away from holding pressure, thereby reducing the amount and probability of bubble formation due to these pressure changes. In emergencies a partial pressure of 0.6 bar of oxygen can be tolerated for over 24 hours, but this is avoided where possible. Carbon dioxide can also be tolerated at higher levels for limited periods. US Navy limit is 0.02 bar for up to 4 hours. Nitrogen partial pressure starts at 0.79 bar from the initial air content before compression, but tends to decrease over time as the system loses gas to lock operation, and is topped up with helium. [1]

    Deployment of divers Edit

    Deployment of divers from a surface saturation complex requires the diver to be transferred under pressure from the accommodation area to the underwater workplace. This is generally done by using a closed diving bell, also known as a Personnel Transfer Capsule, which is clamped to the lock flange of the accommodation transfer chamber and the pressure equalized with the accommodation transfer chamber for transfer to the bell. The lock doors can then be opened for the divers to enter the bell. The divers will suit up before entering the bell and complete the pre-dive checks. The pressure in the bell will be adjusted to suit the depth at which the divers will lock out while the bell is being lowered, so that the pressure change can be slow without unduly delaying operations. [1]

    The bell is deployed over the side of the vessel or platform using a gantry or A-frame or through a moon pool. Deployment usually starts by lowering the clump weight, which is a large ballast weight suspended from a cable which runs down one side from the gantry, through a set of sheaves on the weight, and up the other side back to the gantry, where it is fastened. The weight hangs freely between the two parts of the cable, and due to its weight, hangs horizontally and keeps the cable under tension. The bell hangs between the parts of the cable, and has a fairlead on each side which slides along the cable as it is lowered or lifted. The bell hangs from a cable attached to the top. As the bell is lowered, the fairleads guide it down the clump weight cables to the workplace. [29]

    The bell umbilical is separate from the divers' umbilicals, which are connected on the inside of the bell. The bell umbilical is deployed from a large drum or umbilical basket and care is taken to keep the tension in the umbilical low but sufficient to remain near vertical in use and to roll up neatly during recovery. [29]

    A device called a bell cursor may be used to guide and control the motion of the bell through the air and the splash zone near the surface, where waves can move the bell significantly. [29]

    Once the bell is at the correct depth, the final adjustments to pressure are made and after final checks, the supervisor instructs the working diver(s) to lock out of the bell. The hatch is at the bottom of the bell and can only be opened if the pressure inside is balanced with the ambient water pressure. The bellman tends the working diver's umbilical through the hatch during the dive. If the diver experiences a problem and needs assistance, the bellman will exit the bell and follow the diver's umbilical to the diver and render whatever help is necessary and possible. Each diver carries back-mounted bailout gas, which should be sufficient to allow a safe return to the bell in the event of an umbilical gas supply failure. [25] : 12

    Breathing gas is supplied to the divers from the surface through the bell umbilical. If this system fails, the bell carries an on-board gas supply which is plumbed into the bell gas panel and can be switched by operating the relevant valves. On-board gas is generally carried externally in several storage cylinders of 50 litres capacity or larger, connected through pressure regulators to the gas panel. [25] : 12

    Helium is a very effective heat transfer material, and divers may lose heat rapidly if the surrounding water is cold. To prevent hypothermia, hot-water suits are commonly used for saturation diving, and the breathing gas supply may be heated. Heated water is produced at the surface and piped to the bell through a hot-water line in the bell umbilical, then is transferred to the divers through their excursion umbilicals. [26] : 10-8 The umbilicals also have cables for electrical power to the bell and helmet lights, and for voice communications and closed circuit video cameras. In some cases the breathing gas is recovered to save the expensive helium. This is done through a reclaim hose in the umbilicals, which ducts exhaled gas exhausted through a reclaim valve on the helmet, through the umbilicals and back to the surface, where the carbon dioxide is scrubbed and the gas boosted into storage cylinders for later use. [ citation needed ]

    Excursions from storage depth Edit

    It is quite common for saturation divers to need to work over a range of depths while the saturation system can only maintain one or two storage depths at any given time. A change of depth from storage depth is known as an excursion, and divers can make excursions within limits without incurring a decompression obligation, just as there are no-decompression limits for surface oriented diving. Excursions may be upward or downward from the storage depth, and the allowed depth change may be the same in both directions, or sometimes slightly less upward than downward. Excursion limits are generally based on a 6 to 8 hour time limit, as this is the standard time limit for a diving shift. [30] These excursion limits imply a significant change in gas load in all tissues for a depth change of around 15m for 6 to 8 hours, and experimental work has shown that both venous blood and brain tissue are likely to develop small asymptomatic bubbles after a full shift at both the upward and downward excursion limits. These bubbles remain small due to the relatively small pressure ratio between storage and excursion pressure, and are generally resolved by the time the diver is back on shift, and residual bubbles do not accumulate over sequential shifts. However, any residual bubbles pose a risk of growth if decompression is started before they are fully eliminated. [30] Ascent rate during excursions is limited, to minimize the risk and amount of bubble formation. [28] [31]

    Decompression from saturation Edit

    Once all the tissue compartments have reached saturation for a given pressure and breathing mixture, continued exposure will not increase the gas loading of the tissues. From this point onward the required decompression remains the same. If divers work and live at pressure for a long period, and are decompressed only at the end of the period, the risks associated with decompression are limited to this single exposure. This principle has led to the practice of saturation diving, and as there is only one decompression, and it is done in the relative safety and comfort of a saturation habitat, the decompression is done on a very conservative profile, minimising the risk of bubble formation, growth and the consequent injury to tissues. A consequence of these procedures is that saturation divers are more likely to suffer decompression sickness symptoms in the slowest tissues, whereas bounce divers are more likely to develop bubbles in faster tissues. [ citation needed ]

    Decompression from a saturation dive is a slow process. The rate of decompression typically ranges between 3 and 6 fsw (0.9 and 1.8 msw) per hour. The US Navy Heliox saturation decompression rates require a partial pressure of oxygen to be maintained at between 0.44 and 0.48 atm when possible, but not to exceed 23% by volume, to restrict the risk of fire [31]

    US Navy heliox saturation decompression table [31]
    Depth Ascent rate
    1600 to 200 fsw (488 to 61 msw) 6 fsw (1.83 msw) per hour
    200 to 100 fsw (61 to 30 msw) 5 fsw (1.52 msw) per hour
    100 to 50 fsw (30 to 15 msw) 4 fsw (1.22 msw) per hour
    50 to 0 fsw (15 to 0 msw) 3 fsw (0.91 msw) per hour

    For practicality the decompression is done in increments of 1 fsw at a rate not exceeding 1 fsw per minute, followed by a stop, with the average complying with the table ascent rate. Decompression is done for 16 hours in 24, with the remaining 8 hours split into two rest periods. A further adaptation generally made to the schedule is to stop at 4 fsw for the time that it would theoretically take to complete the decompression at the specified rate, i.e. 80 minutes, and then complete the decompression to surface at 1 fsw per minute. This is done to avoid the possibility of losing the door seal at a low pressure differential and losing the last hour or so of slow decompression. [31]

    Decompression following a recent excursion Edit

    Neither the excursions nor the decompression procedures currently in use have been found to cause decompression problems in isolation. However, there appears to be significantly higher risk when excursions are followed by decompression before non-symptomatic bubbles resulting from excursions have totally resolved. Starting decompression while bubbles are present appears to be the significant factor in many cases of otherwise unexpected decompression sickness during routine saturation decompression. [30] The Norwegian standards do not allow decompression following directly on an excursion. [27]

    The "saturation system", "saturation complex" or "saturation spread" typically comprises either an underwater habitat or a surface complex made up of a living chamber, transfer chamber and submersible decompression chamber, [32] which is commonly referred to in commercial diving and military diving as the diving bell, [33] PTC (personnel transfer capsule) or SDC (submersible decompression chamber). [1] The system can be permanently placed on a ship or ocean platform, but is more commonly capable of being moved from one vessel to another by crane. To facilitate transportation of the components, it is standard practice to construct the components as units based on the intermodal container system, some of which may be stackable to save deck space. The entire system is managed from a control room ("van"), where depth, chamber atmosphere and other system parameters are monitored and controlled. The diving bell is the elevator or lift that transfers divers from the system to the work site. Typically, it is mated to the system utilizing a removable clamp and is separated from the system tankage bulkhead by a trunking space, a kind of tunnel, through which the divers transfer to and from the bell. At the completion of work or a mission, the saturation diving team is decompressed gradually back to atmospheric pressure by the slow venting of system pressure, at an average of 15 metres (49 ft) to 30 metres (98 ft) per day (schedules vary). Thus the process involves only one ascent, thereby mitigating the time-consuming and comparatively risky process of in-water, staged decompression or sur-D O2 operations normally associated with non-saturation mixed gas diving. [2] More than one living chamber can be linked to the transfer chamber through trunking so that diving teams can be stored at different depths where this is a logistical requirement. An extra chamber can be fitted to transfer personnel into and out of the system while under pressure and to treat divers for decompression sickness if this should be necessary. [34]

    The divers use surface supplied umbilical diving equipment, utilizing deep diving breathing gas, such as helium and oxygen mixtures, stored in large capacity, high pressure cylinders. [2] The gas supplies are plumbed to the control room, where they are routed to supply the system components. The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water. The bell also is fitted with exterior mounted breathing gas cylinders for emergency use. [34]

    While in the water the divers will often use a hot water suit to protect against the cold. [35] The hot water comes from boilers on the surface and is pumped down to the diver via the bell's umbilical and then through the diver's umbilical. [34]

    Personnel transfer capsule Edit

    A closed diving bell, also known as personnel transfer capsule or submersible decompression chamber, is used to transport divers between the workplace and the accommodations chambers. The bell is a cylindrical or spherical pressure vessel with a hatch at the bottom, and may mate with the surface transfer chamber at the bottom hatch or at a side door. Bells are usually designed to carry two or three divers, one of whom, the bellman, stays inside the bell at the bottom and is stand-by diver to the working divers. Each diver is supplied by an umbilical from inside the bell. The bell has a set of high pressure gas storage cylinders mounted on the outside containing on-board reserve breathing gas. The on-board gas and main gas supply are distributed from the bell gas panel, which is controlled by the bellman. The bell may have viewports and external lights. [31] The divers' umbilicals are stored on racks inside the bell during transfer, and are tended by the bellman during the dive. [26] : ch.13

    Bell handling system Edit

    The bell is deployed from a gantry or A-frame, also known as a bell launch and recovery system (LARS), [26] : ch.13 on the vessel or platform, using a winch. Deployment may be over the side or through a moon pool. [31]

    • The handling system must be able to support the dynamic loads imposed by operating in a range of weather conditions.
    • It must be able to move the bell through the air/water interface (splash zone) in a controlled way, fast enough to avoid excessive movement caused by wave action.
    • A bell cursor may be used to limit lateral motion through and above the splash zone.
    • It must keep the bell clear of the vessel or platform to prevent impact damage or injury.
    • It must have sufficient power for fast retrieval of the bell in an emergency, and fine control to facilitate mating of the bell and transfer flange, and to accurately place the bell at the bottom.
    • It must include a system to move the bell between the mating flange of the transfer chamber and the launch/retrieval position.

    Transfer chamber Edit

    The transfer chamber is where the bell is mated to the surface saturation system for transfer under pressure (TUP). It is a wet surface chamber where divers prepare for a dive and strip off and clean their gear after return. Connection to the bell may be overhead, through the bottom hatch of the bell, or lateral, through a side door. [34]

    Accommodation chambers Edit

    The accommodation chambers may be as small as 100 square feet. [36] This part is generally made of multiple compartments, including living, sanitation, and rest facilities, each a separate unit, joined by short lengths of cylindrical trunking. It is usually possible to isolate each compartment from the others using internal pressure doors. [34] Catering and laundry are provided from outside the system and locked on and out as required.

    Recompression chamber Edit

    A recompression chamber may be included in the system so that divers can be given treatment for decompression sickness without inconveniencing the rest of the occupants. The recompression chamber may also be used as an entry lock, and to decompress occupants who may need to leave before scheduled. [ citation needed ]

    Mating flange for transportable chamber Edit

    One or more of the external doors may be provided with a mating flange or collar to suit a portable or transportable chamber, which can be used to evacuate a diver under pressure. The closed bell can be used for this purpose, but lighter and more easily portable chambers are also available. [ citation needed ] There will usually also be a mating flange for the hyperbaric rescue and escape system.

    Supply lock Edit

    A small lock is used for transfer of supplies into and out of the pressurized system. This would normally include food, medical supplies, clothing, bedding etc. [ citation needed ]

    Trunking Edit

    The pressurised compartments of the system are connected through access trunking: relatively short and small diameter spools bolted between the external flanges of the larger compartments, with pressure seals, forming passageways between the chambers, which can be isolated by pressure doors. [34]

    Life support systems Edit

    The life support system provides breathing gas and other services to support life for the personnel under pressure. It includes the following components: [34]

    • Breathing gas supply, distribution and recycling equipment: scrubbers, filters, boosters, compressors, mixing, monitoring, and storage facilities
    • Chamber climate control system - control of temperature and humidity, and filtration of gas
    • Instrumentation, control, monitoring and communications equipment
    • Fire suppression systems
    • Sanitation systems

    The life support system for the bell provides and monitors the main supply of breathing gas, and the control station monitors the deployment and communications with the divers. Primary gas supply, power and communications to the bell are through a bell umbilical, made up from a number of hoses and electrical cables twisted together and deployed as a unit. [31] This is extended to the divers through the diver umbilicals. [34]

    The accommodation life support system maintains the chamber environment within the acceptable range for health and comfort of the occupants. Temperature, humidity, breathing gas quality sanitation systems and equipment function are monitored and controlled. [31]

    Hot water system Edit

    Divers working in cold water, particularly when breathing helium based gases, which increase the rate of heat transfer, may rapidly lose body heat and suffer from hypothermia, which is unhealthy, can be life-threatening, and reduces diver effectiveness. This can be ameliorated with a hot water system. A diver hot water system heats filtered seawater and pumps it to the divers through the bell and diver umbilicals. This water is used to heat the breathing gas before it is inhaled, and flows through the diver's exposure suit to keep the diver warm. [31] [34]

    Communication systems Edit

    Helium and high pressure both cause hyperbaric distortion of speech. The process of talking underwater is influenced by the internal geometry of the life support equipment and constraints on the communications systems as well as the physical and physiological influences of the environment on the processes of speaking and vocal sound production. [37] : 6,16 The use of breathing gases under pressure or containing helium causes problems in intelligibility of diver speech due to distortion caused by the different speed of sound in the gas and the different density of the gas compared to air at surface pressure. These parameters induce changes in the vocal tract formants, which affect the timbre, and a slight change of pitch. Several studies indicate that the loss in intelligibility is mainly due to the change in the formants. [38]

    The difference in density of the breathing gas causes a non-linear shift of low-pitch vocal resonance, due to resonance shifts in the vocal cavities, giving a nasal effect, and a linear shift of vocal resonances which is a function of the velocity of sound in the gas, known as the Donald Duck effect. Another effect of higher density is the relative increase in intensity of voiced sounds relative to unvoiced sounds. The contrast between closed and open voiced sounds and the contrast between voiced consonants and adjacent vowels decrease with increased pressure. [39] Change of the speed of sound is relatively large in relation to depth increase at shallower depths, but this effect reduces as the pressure increases, and at greater depths a change in depth makes a smaller difference. [38] Helium speech unscramblers are a partial technical solution. They improve intelligibility of transmitted speech to surface personnel. [39]

    The communications system may have four component systems. [31]

    • The hardwired intercom system, an amplified voice system with speech unscrambler to reduce the pitch of the speech of the occupants of the pressurized system. This system will provide communications between the main control console and the bell and accommodation chambers. This two-way system is the primary communications mode.
    • Wireless through-water communications between bell and main control console is a backup system in case of failure of the hardwired system with the bell.
    • Closed circuit video from cameras on the bell and diver helmets allow visual monitoring of the dive and the divers by the supervisor.
    • A sound powered phone system may be provided as a backup voice communication system between bell and control console

    Bulk gas supplies Edit

    Gas storage and blending equipment are provided to pressurize and flush the system, and treatment gases should be available appropriate to the planned storage depths. Bulk stock of premixed gas is usually provided to suit the planned depth of the operation, and separate bulk stock of helium and oxygen to make up additional requirements, adjust chamber gas composition as the oxygen is used up, and mix decompression gas. [34]

    Bulk gas is usually stored in manifolded groups of storage cylinders known as "quads", which usually carry about 16 high pressure cylinders, each of about 50 litres internal volume mounted on a frame for ease of transport, or larger frames carrying larger capacity high pressure "tubes". These tube frames are usually designed to be handled by intermodal container handling equipment, so are usually made in one of the standard sizes for intermodal containers. [ citation needed ]

    Gas reclaim systems Edit

    • BGP: bell gas panel
    • S1: first water separator
    • BP1: bell back-pressure regulator
    • U: bell umbilical
    • F1: first gas filter
    • BP2: topside back-pressure regulator
    • R1, R2: serial gas receivers
    • F2: second gas filter
    • B: booster pump
    • Sc1, Sc2: parallel scrubbers
    • C: gas cooler
    • S2: last water separator
    • VT: volume tank
    • PR: pressure regulator
    • MGP: main gas panel

    A helium reclaim system (or push-pull system) may be used to recover helium based breathing gas after use by the divers as this is more economical than losing it to the environment in open circuit systems. [32] The recovered gas is passed through a scrubber system to remove carbon dioxide, filtered to remove odours and other impurities, and pressurised into storage containers, where it may be mixed with oxygen to the required composition. [40] Alternatively the recycled gas can be more directly recirculated to the divers. [41]

    During extended diving operation very large amounts of breathing gas are used. Helium is an expensive gas and can be difficult to source and supply to offshore vessels in some parts of the world. A closed circuit gas reclaim system can save around 80% of gas costs by recovering about 90% of the helium based breathing mixture. Reclaim also reduces the amount of gas storage required on board, which can be important where storage capacity is limited. Reclaim systems are also used to recover gas discharged from the saturation system during decompression. [40]

    A reclaim system will typically consist of the following components: [40] [41]

    • A reclaim control console, which controls and monitors the booster pump, oxygen addition, diver supply pressure, exhaust hose pressure and make-up gas addition.
    • A gas reprocessing unit, with low-pressure carbon dioxide scrubber towers, filters' receivers and back-pressure regulator which will remove carbon dioxide and excess moisture in a condensation water trap. Other gases and odours can be removed by activated carbon filters.
    • A gas booster, to boost the pressure of the reclaimed gas to the storage pressure.
    • A gas volume tank
    • A storage system of pressure vessels to hold the boosted and reconstituted gas mixture until it is used. This functions as a buffer to allow for the variations of gas volume in the rest of the system due to pressure changes.
    • Dive control panel
    • A bell gas supply panel, to control the supply of gas to the bell.
    • The bell umbilical, with the supply and exhaust hoses between the topside system and the bell.
    • Internal bell gas panel to supply the gas to the divers, and bell reclaim equipment, which controls the exhaust hose back-pressure, and can shut off the reclaim hose if the diver's gas supply is interrupted. A scrubber for the bell atmosphere and water trap would be included.
    • Diver excursion umbilicals, with supply and exhaust hoses between the bell and the divers
    • Reclaim helmets which supply gas to the divers on demand, with reclaim back-pressure regulators which exhaust the exhaled gas to the return line.
    • Bell back-pressure regulator with water trap

    In operation the gas supply from the reclaim system is connected to the topside gas panel, with a backup supply at a slightly lower pressure from mixed gas storage which will automatically cut in if the reclaim supply pressure drops. The bellman will set onboard gas supply to a slightly lower pressure than surface supply pressure to the bell gas panel, so that it will automatically cut in if surface supply is lost. After locking out of the bell the diver will close the diverter valve and open the return valve on the helmet, to start the gas reclaim process. Once this is running, the reclaim control panel will be adjusted to make up the metabolic oxygen usage of the diver into the returned gas. This system will automatically shut down oxygen addition if the flow of exhaled gas from the diver fails, to avoid an excessive oxygen fraction in the recycled gas. There is an indicator light to show whether the return gas is flowing. [41]

    The gas supplied to the diver's helmet passes through the same hoses and demand valve as for the open circuit system, but the exhaled gas passes out into the reclaim valve at slightly above ambient pressure, which is considerably above atmospheric pressure, so the flow must be controlled to prevent dropping the helmet internal pressure and causing the demand valve to free-flow. This is achieved by using back-pressure regulators to control the pressure drop in stages. The reclaim valve itself is a demand triggered back-pressure regulator, and there is another back pressure regulator at the bell gas panel, and one at the surface before the receiver tanks. Each of these back-pressure regulators is set to allow about a 1 bar pressure drop. [41]

    Exhaust gas returns to the bell through the diver's umbilical exhaust hose, where it passes through a water separator and trap then through a back-pressure regulator which controls the pressure in the exhaust hose and which can be monitored on a pressure gauge in the bell and adjusted by the bellman to suit the excursion depth of the diver. The gas then passes through the bell umbilical exhaust hose to the surface via a non-return valve and another water trap. When the gas enters the surface unit it goes through a coalescing water separator and micron particle filter, and a float valve, which protects the reclaim system from large volumes of water in the event of a leak at depth. Another back-pressure regulator at the surface controls the pressure in the bell umbilical. The gas then passes into the receiver tanks, where oxygen is added at a flow rate calculated to compensate for metabolic use by the diver. [34]

    Before entering the boosters, the gas passes through a 0.1 micron filter. The gas is then boosted to storage pressure. Redundant boosters are provided to keep the system running while a booster is serviced. The boosters are automatically controlled to match the diver's gas consumption, and the boosted gas passes through a scrubber where the carbon dioxide is removed by a material like sodalime. Like the boosters, there are at least two scrubbers in parallel, so that they can be isolated, vented and repacked alternately while the system remains in operation. The gas then passes through a cooling heat exchanger to condense out any remaining moisture, which is removed by another 1 micon coalescing filter before it reaches the volume storage tank, where it remains until returned to the gas panel to be used by the divers. While in the volume tank, the gas can be analysed to ensure that it is suitable for re-use, and that the oxygen fraction is correct and carbon dioxide has been removed to specification before it is delivered to the divers. [34] If necessary any lost gas can be compensated by topping up the volume tank from the high pressure storage. Gas from the volume tank is fed to the topside gas panel to be routed back to the bell and diver. [41]

    Sanitation system Edit

    The sanitation system includes hot and cold water supply for washbasins and showers, drainage, and marine toilets with holding tank and discharge system. [31]

    Control consoles Edit

    It is common for the control room to be installed in an ISO intermode container for convenience of transport.There are three main control panels, for life support, dive control and gas management. [42]

    Gas management panel Edit

    The gas management panel includes pressure regulation of gases from high pressure storage, and distribution to the consumers. Gases will include air, oxygen and heliox mixes [42]

    Saturation control panel Edit

    The chamber control panel will typically include depth gauges for each compartment, including trunking, blowdown and exhaust valves, oxygen monitoring and other gas analysis equipment, make-up system for oxygen replenishment, valves for supplying therapeutic breathing mixture, closed circuit television monitoring displays, and monitoring systems with alarms for temperature and pressure in the system chambers. [42]

    Dive control panel Edit

    The dive control panel will include depth gauges for bell internal and external pressure, diver and bellman depth, and trunking pressure for transfer to the accommodation chambers. There will also be breathing gas pressure gauges and control valves for each diver, and blowdown and exhaust valves for the bell interior, diver communications systems with speech unscramblers, a through-water emergency communications system to the bell, controls, monitors and recording equipment for helmet and bell mounted video cameras, oxygen analysers for diver breathing gas, oxygen and carbon dioxide analysers for bell and reclaim gas, alarms for reclaim gas flow, dynamic positioning and hot water supply. [42]

    Fire suppression system Edit

    Firefighting systems include hand held fire extinguishers to automatic deluge systems. Special fire extinguishers which do not use toxic materials must be used. In the event of a fire, toxic gases may be released by burning materials, and the occupants will have to use the built-in breathing systems (BIBS) until the chamber gas has been flushed sufficiently. When a system with oxygen partial pressure 0.48 bar is pressurized below about 70 msw (231fsw), the oxygen fraction is too low to support combustion (less than 6%), and the fire risk is low. During the early stages of compression and towards the end of decompression the oxygen levels will support combustion, and greater care must be taken. [31]

    Built in breathing systems Edit

    Built in breathing systems are installed for emergency use and for treatment of decompression sickness. They supply breathing gas appropriate to the current function, which is supplied from outside the pressurized system and also vented to the exterior, so the exhaled gases do not contaminate the chamber atmosphere. [31]

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