Multiple decompressions per day over multiple days can increase the risk of decompression sickness because of the buildup of asymptomatic bubbles, which reduce the rate of off-gassing and are not accounted for in most decompression algorithms.
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By limiting the number of decompressions in this way, the risk of decompression sickness is significantly reduced, and the time spent decompressing is minimised. It is a very specialized form of diving; of the 3,300 commercial divers employed in the United States in 2015, only 336 were saturation divers.
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Other factors which can affect decompression risk include oxygen concentration, carbon dioxide levels, body position, vasodilators and constrictors, positive or negative pressure breathing. and dehydration (blood volume). Individual susceptibility to decompression sickness has components which can be attributed to a specific cause, and components which appear to be random. The random component makes successive decompressions a poor test of susceptibility.
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Most divers do longer decompressions; however, some groups like the WKPP have been pioneering the use of shorter decompression times by including deep stops. Any inert gas that is breathed under pressure can form bubbles when the ambient pressure decreases. Very deep dives have been made using hydrogen-oxygen mixtures (hydrox), but controlled decompression is still required to avoid DCS.
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During his diving career, he set numerous depth and cave penetration records. Exley is one of only eleven men in the history of technical SCUBA diving to dive below , as well as the first. His carefully planned multistage decompressions from these dives, in open water (not in a decompression tank), sometimes required times of as much as 13.5 hours. However, he never suffered a classic case of decompression sickness in his career.
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In personal dive computers, they produce a real- time estimate of decompression status and display it for the diver. Two different concepts have been used for decompression modelling. The first assumes that dissolved gas is eliminated while in the dissolved phase, and that bubbles are not formed during asymptomatic decompression. The second, which is supported by experimental observation, assumes that bubbles are formed during most asymptomatic decompressions, and that gas elimination must consider both dissolved and bubble phases.
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In repetitive diving, the slower tissues can accumulate gas day after day, if there is insufficient time for the gas to be eliminated between dives. This can be a problem for multi- day multi-dive situations. Multiple decompressions per day over multiple days can increase the risk of decompression sickness because of the build up of asymptomatic bubbles, which reduce the rate of off-gassing and are not accounted for in most decompression algorithms. Consequently, some diver training organisations make extra recommendations such as taking "the seventh day off".
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The caissons were massive metal boxes with varying dimensions, but each contained walls. Sandhogs entered the tunnel through a series of airlocks, and could only remain inside of the tunnel for a designated time period. On exiting the tunnel, sandhogs had to undergo controlled decompression to avoid decompression sickness or "the bends", a condition in which nitrogen bubbles form in the blood from rapid decompression. The rate of decompression rate for sandhogs working on the Hudson River Tunnel was described as being "so small as to be negligible". Sandhogs underwent such decompressions 756,000 times throughout the course of construction.
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The risk of decompression sickness is significantly reduced by minimizing the number of decompressions, and by decompressing at a very conservative rate. The saturation system typically comprises a complex made up of a living chamber, transfer chamber and submersible decompression chamber, which is commonly referred to in commercial diving and military diving as the diving bell, PTC (personnel transfer capsule) or SDC (submersible decompression chamber). The system can be permanently installed on a ship or ocean platform, but is usually capable of being transferred between vessels. The system is managed from a control room, where depth, chamber atmosphere and other system parameters are monitored and controlled.
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However, some saturation decompression schedules specifically do not allow an decompression to start with an upward excursion. Neither the excursions nor the decompression procedures currently in use (2016) have been found to cause decompression problems in isolation, but 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. Application of a bubble model in 1985 allowed successful modelling of conventional decompressions, altitude decompression, no-stop thresholds, and saturation dives using one setting of four global nucleation parameters.
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However, some saturation decompression schedules specifically do not allow an decompression to start with an upward excursion. Neither the excursions nor the decompression procedures currently in use (2016) have been found to cause decompression problems in isolation, but 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. Application of a bubble model in 1985 allowed successful modelling of conventional decompressions, altitude decompression, no-stop thresholds, and saturation dives using one setting of four global nucleation parameters.
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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 rates of about of 15 to 30 msw (50 to 100 fsw) per day, (schedules vary). Thus the process involves only one ascent, thereby mitigating the time- consuming and comparatively risky process of multiple decompressions normally associated with non-saturation ("bounce diving") operations. The chamber gas mixture is typically controlled to maintain a nominally constant partial pressure of oxygen of between 0.3 and 0.5 bar during most of the decompression (0.44 to 0.48 bar on US Navy schedule), which is below the upper limit for long term exposure. NOAA has used rather different saturation decompression schedules for relatively shallow (less than 100 fsw) air and nitrox saturation dives, which use oxygen breathing when pressure is reduced to less than 55 fsw.
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