The US Navy has used several decompression models from which their published decompression tables and authorized diving computer algorithms have been derived. The original C&R tables used a classic multiple independent parallel compartment model based on the work of J.S.Haldane in England in the early 20th century, using a critical ratio exponential ingassing and outgassing model. Later they were modified by O.D. Yarborough and published in 1937. A version developed by Des Granges was published in 1956. Further developments by M.W. Goodman and Robert D. Workman using a critical supersaturation approach to incorporate M-values, and expressed as an algorithm suitable for programming were published in 1965, and later again a significantly different model, the VVAL 18 exponential/linear model was developed by Edward D. Thalmann, using an exponential ingassing model and a combined exponential and linear outgassing model, which was further developed by Gerth and Doolette and published in Revision 6 of the US Navy Diving Manual as the 2008 tables.
Besides the air and heliox tables for open circuit bounce dives, the US Navy has published a variety of hyperbaric treatment schedules, decompression tables for open and closed circuit heliox and nitrox, tables incorporating surface decompression on oxygen, a system for modifying tables for use at high altitudes (Cross corrections), and saturation tables for various breathing gas mixtures. Many of these tables have been tested on human subjects, frequently with a result of symptomatic decompression sickness, and for this reason their test results are considered some of the most reliable available.
US Navy tables have generally been freely available for use by the general public, and have often been modified to further reduce risk, as commercial and recreational divers do not always fit the physical requirements for military divers, may not have a recompression chamber on site to manage decompression sickness on those occasions when it does occur, and may prefer to operate at a lower risk than military personnel. Several recreational diving tables were originally based on US Navy diving tables.
In 1912, Chief Gunner George D. Stillson of the United States Navy created a program to test and refine Haldane's tables. [1] This program ultimately led to the first publication of the United States Navy Diving Manual and the establishment of a Navy Diving School in Newport, Rhode Island. Diver training programs were later cut at the end of World War I.
The first decompression tables produced for the U.S. Navy were developed by the Bureau of Construction and Repair and published in 1915, and were consequently known as the C&R tables. [2] They were derived from a Haldanean model, with oxygen decompression, to depths up to 300 ft on air, and were successfully used to depths of slightly over 300 ft [3] : 3–1
In 1939, after the recovery of USS Squalus, tables were published for surface supplied Heliox diving. [6] : 1–17
Although recompression and slow decompression were the accepted treatment, there was not yet a standard for either the recompression pressure or the rate of decompression. This changed when the first standard table for recompression treatment with air was published in the US Navy Diving Manual in 1924. These tables were not entirely successful - there was a 50% relapse rate, and the treatment, though fairly effective for mild cases, was less effective in serious cases. [9]
In 1965,[ clarification needed ] M.W. Goodman and Robert D. Workman introduced recompression tables using oxygen to accelerate elimination of inert gas. [15] [16]
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, [17] 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. [18]
| 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. [18]
In 1983, Edward D. Thalmann published the E-L model for constant PO2 nitrox and heliox closed circuit rebreathers, [19] in 1984 published U.S. Navy Exponential-Linear algorithm and tables for constant PO2 Nitrox closed circuit rebreather (CCR) applications, [20] and in 1985 Thalmann extended use of the E-L model for constant PO2 heliox closed circuit rebreathers. [21]
In 2007, Wayne Gerth and David J. Doolette published VVal 18 and VVal 18M parameter sets for tables and programs based on the Thalmann E-L algorithm, and produced an internally compatible set of decompression tables for open circuit and CCR on air and nitrox, including in water air/oxygen decompression and surface decompression on oxygen. [20]
In 2008 the US Navy Diving Manual Revision 6 was published, which includes a version of the 2007 tables by Gerth & Doolette. [14] The air decompression tables in Revision 6 of the U.S. Navy Diving Manual combine decompression tables for air diving with schedules for decompression on air, air and in-water oxygen, and surface decompression using oxygen. The tables were computed using version VVal-18M of the Thalmann exponential-linear decompression model.
The Thalmann Algorithm (VVAL 18) is a deterministic decompression model originally designed in 1980 to produce a decompression schedule for divers using the US Navy Mk15 rebreather. [22] It was developed by Capt. Edward D. Thalmann, MD, USN, who did research into decompression theory at the Naval Medical Research Institute, Navy Experimental Diving Unit, State University of New York at Buffalo, and Duke University. The algorithm forms the basis for the US Navy mixed gas and standard air dive tables published in US Navy Diving Manual Revisions 6 and 7. [23] This decompression model is also referred to as the Linear–Exponential model or the Exponential–Linear model. [24]
As of January 2023 the currently approved decompression tables are listed in Revision 7 of the US Navy Diving Manual.
 | This section needs expansionwith: differences in the tables in R7. You can help by adding to it. (January 2023) |
In 1984 the US Navy diving computer (UDC) which was based on a 9 tissue model by Edward D. Thalmann of the Naval Experimental Diving Unit (NEDU), Panama City. Divetronic AG completed the UDC development – as it had been started by the chief engineer Kirk Jennings of the Naval Ocean System Center, Hawaii, and Thalmann of the NEDU – by adapting the Deco Brain for US Navy warfare use and for their 9-tissue MK-15 mixed gas model under a research and development contract with the US Navy.[ citation needed ]
In 2001, the US Navy approved the use of Cochran NAVY decompression computer with the VVAL 18 Thalmann algorithm for Special Warfare operations. [25] [26] [27]
As of 2023, Shearwater Research has supplied dive computers to the US Navy with an exponential/linear algorithm bases on the Thalman algorithm since Cochran Undersea Technology closed down after the death of the owner. This algorithm is not as of 2024 available to the general public on Shearwater computers, although the algorithm is freely available and known to be lower risk than the Buhlmann algorithm for mixed gas and constant set-point CCR diving at deeper depths, which is the primary market for Shearwater products. [28] [29]
It is important that any theory be validated by carefully controlled testing procedures. As testing procedures and equipment become more sophisticated, researchers learn more about the effects of decompression on the body. Initial research focused on producing dives that were free of recognizable symptoms of decompression sickness (DCS). With the later use of Doppler ultrasound testing, it was realized that bubbles were forming within the body even on dives where no DCI signs or symptoms were encountered. This phenomenon has become known as "silent bubbles". The presence of venous gas emboli is considered a low specificity predictor of decompression sickness, but their absence is recognised to be a sensitive indicator of low risk decompression, therefore the quantitative detection of VGE is thought to be useful as an indicator of decompression stress when comparing decompression strategies, or assessing the efficiency of procedures. [30]
The US Navy 1956 tables were based on limits determined by external DCS signs and symptoms. Later researchers were able to improve on this work by adjusting the limitations based on Doppler testing. However the US Navy CCR tables based on the Thalmann algorithm also used only recognisable DCS symptoms as the test criteria. [31] [24] Since the testing procedures are lengthy and costly, and there are ethical limitations on experimental work on human subjects with injury as an endpoint, it is common practice for researchers to make initial validations of new models based on experimental results from earlier trials. This has some implications when comparing models. [3] : Ch10
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At altitude, atmospheric pressure is lower than at sea level, so surfacing at the end of an altitude dive leads to a greater relative reduction in pressure and an increased risk of decompression sickness compared to the same dive profile at sea level. [34] The dives are also typically carried out in freshwater at altitude so it has a lower density than seawater used for calculation of decompression tables. [34] The amount of time the diver has spent acclimatising at altitude is also of concern as divers with gas loadings near those of sea level may also be at an increased risk. [34] The US Navy recommends waiting 12 hours following arrival at altitude before performing the first dive. [35] cut to move The tissue supersaturation following an ascent to altitude can also be accounted for by considering it to be residual nitrogen and allocating a residual nitrogen group when using tables with this facility. [35]
The most common of the modifications to decompression tables at altitude are the "Cross Corrections" which use a ratio of atmospheric pressure and sea level to that of the altitude to provide a conservative equivalent sea level depth. [36] [37] The procedure is described in detail in the U.S. Navy Diving Manual
| | This section needs expansionwith: describe the procedure. Is R7 still using cross corrections?. You can help by adding to it. (January 2023) |
Decompression sickness is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working at great depths must undergo by only decompressing divers once at the end of the diving operation, which may last days to weeks, having them remain under pressure for the whole period. A diver breathing pressurized gas accumulates dissolved inert gas used in the breathing mixture to dilute the oxygen to a non-toxic level in the tissues, which can cause potentially fatal decompression sickness if permitted to come out of solution within the body tissues; hence, returning to the surface safely requires lengthy decompression so that the inert gases can be eliminated via the lungs. Once the dissolved gases in a diver's tissues reach the saturation point, however, decompression time does not increase with further exposure, as no more inert gas is accumulated.
In-water recompression (IWR) or underwater oxygen treatment is the emergency treatment of decompression sickness (DCS) by returning the diver underwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a procedure that exposes the diver to significant risk which should be compared with the risk associated with the available options and balanced against the probable benefits. Some authorities recommend that it is only to be used when the time to travel to the nearest recompression chamber is too long to save the victim's life; others take a more pragmatic approach and accept that in some circumstances IWR is the best available option. The risks may not be justified for case of mild symptoms likely to resolve spontaneously, or for cases where the diver is likely to be unsafe in the water, but in-water recompression may be justified in cases where severe outcomes are likely if not recompressed, if conducted by a competent and suitably equipped team.
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of breathing gas for the occupants.
Capt. Edward Deforest Thalmann, USN (ret.) was an American hyperbaric medicine specialist who was principally responsible for developing the current United States Navy dive tables for mixed-gas diving, which are based on his eponymous Thalmann Algorithm (VVAL18). At the time of his death, Thalmann was serving as assistant medical director of the Divers Alert Network (DAN) and an assistant clinical professor in anesthesiology at Duke University's Center for Hyperbaric Medicine and Environmental Physiology.
The Thalmann Algorithm is a deterministic decompression model originally designed in 1980 to produce a decompression schedule for divers using the US Navy Mk15 rebreather. It was developed by Capt. Edward D. Thalmann, MD, USN, who did research into decompression theory at the Naval Medical Research Institute, Navy Experimental Diving Unit, State University of New York at Buffalo, and Duke University. The algorithm forms the basis for the current US Navy mixed gas and standard air dive tables. The decompression model is also referred to as the Linear–Exponential model or the Exponential–Linear model.
In physiology, isobaric counterdiffusion (ICD) is the diffusion of different gases into and out of tissues while under a constant ambient pressure, after a change of gas composition, and the physiological effects of this phenomenon. The term inert gas counterdiffusion is sometimes used as a synonym, but can also be applied to situations where the ambient pressure changes. It has relevance in mixed gas diving and anesthesiology.
The United States Navy Experimental Diving Unit is the primary source of diving and hyperbaric operational guidance for the US Navy. It is located within the Naval Support Activity Panama City in Panama City Beach, Bay County, Florida.
The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gases from the diver's body which accumulate during ascent, largely during pauses in the ascent known as decompression stops, and after surfacing, until the gas concentrations reach equilibrium. Divers breathing gas at ambient pressure need to ascend at a rate determined by their exposure to pressure and the breathing gas in use. A diver who only breathes gas at atmospheric pressure when free-diving or snorkelling will not usually need to decompress. Divers using an atmospheric diving suit do not need to decompress as they are never exposed to high ambient pressure.
To prevent or minimize decompression sickness, divers must properly plan and monitor decompression. Divers follow a decompression model to safely allow 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 in the context of diving derives from the reduction in ambient pressure experienced by 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.
Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to the tissues and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure, but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure, are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms caused by decompression occur during or within a relatively short period of hours, or occasionally days, after a significant pressure reduction.
Hyperbaric treatment schedules or hyperbaric treatment tables, are planned sequences of events in chronological order for hyperbaric pressure exposures specifying the pressure profile over time and the breathing gas to be used during specified periods, for medical treatment. Hyperbaric therapy is based on exposure to pressures greater than normal atmospheric pressure, and in many cases the use of breathing gases with oxygen content greater than that of air.
There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures.
The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure. It involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs, or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.
A built-in breathing system is a source of breathing gas installed in a confined space where an alternative to the ambient gas may be required for medical treatment, emergency use, or to minimise a hazard. They are found in diving chambers, hyperbaric treatment chambers, and submarines.
The U.S. Navy Diving Manual is a book used by the US Navy for diver training and diving operations.
Inner ear decompression sickness, (IEDCS) or audiovestibular decompression sickness is a medical condition of the inner ear caused by the formation of gas bubbles in the tissues or blood vessels of the inner ear. Generally referred to as a form of decompression sickness, it can also occur at constant pressure due to inert gas counterdiffusion effects.
