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Ratio decompression
Ratio decompression (usually referred to in abbreviated form as ratio deco) is a technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer. It is generally taught as part of the "DIR" philosophy of diving promoted by organisations such Global Underwater Explorers (GUE) Innerspace Explorers (ISE) and Unified Team Diving (UTD) at the advanced technical diving level. It is designed for decompression diving executed deeper than standard recreational diving depth limits using trimix as a "bottom mix" breathing gas.
There have been three iterations of UTD Ratio Deco, The latest as of 2021 is RD 3.0, which has less emphasis on deep stops than RD 2.0.
The physiology behind the off-gassing of nitrogen or helium absorbed by the body from breathing gases under pressure has never been definitively established, particularly in relation to the formation of bubbles in the body's tissues, and a number of different algorithms have been developed over the years, based on simplified hypotheses of gas transport and absorption in body tissues, modified to fit empirical data, to predict the rate of off-gassing to reduce the risk of decompression sickness in divers to an acceptable level. However, these models do not describe the individual physiology of the diver accurately: divers have been known to suffer symptomatic decompression sickness whilst diving within the limits of dive tables or dive computers (sometimes referred to as an "undeserved hit"), and divers have exceeded No Decompression Limits but remained asymptomatic.
While Ratio Decompression is not a complete decompression model, it most resembles those of Bühlmann algorithm, and the Varying Permeability Model algorithm, with emphasis on the use of deep stops and gradient factors.[citation needed] It is a type of simplified curve fitting applied to a model decompression profile considered by the author of the model to be acceptable based on experience.
A conventional decompression profile, based on a dissolved gas model algorithm, will result in a diver ascending relatively quickly through shorter deep stops before spending a great deal of time at the shallower stops (resulting in a much sharper angle in the depth/time graph of the ascent profile), ratio deco will allow a diver to dynamically[clarification needed] take a total decompression obligation[clarification needed] for a given dive and create a profile which makes better use[clarification needed] the most effective parts[clarification needed] of the decompression profile, and spends comparatively less time at the less effective stops[clarification needed] (resulting in a much softer[clarification needed][weasel words] curve in the depth/time graph of the ascent profile).[citation needed]
The basis for calculating a decompression schedule using ratio decompression is actually relatively simple (and certainly much simpler than the extremely complicated algorithms used by dive computers). The following represents a slightly simplified summary of the process.[clarification needed] Not all versions of ratio deco use exactly the same procedure.
The starting point is to ascertain the correct ratio (from whence the technique gets its name) of the amount of total decompression time as a ratio to the total bottom time. This ratio is fixed solely by reference to depth. Although on traditional tables the amount of decompression would vary according to time at depth, the basis of the theory that most dives will operate within a range of normalcy[clarification needed] which makes the use of fixed ratios permissible.[clarification needed] Certain depths establish certain ratios; a 1:1 ratio occurs at approximately 150 feet (46 m); a 2:1 ratio occurs at approximately 220 feet (67 m). Between these depths, for each 10 feet (3 m) deeper or shallower than a fixed ratio depth, the diver will then add or subtract a specified number of minutes to their total decompression time.[citation needed] Accordingly, once the diver knows their planned depth and time, they can look up the most proximate ratio, calculate the difference in depths, and add or subtract the appropriate number of minutes from their total bottom time to give a total decompression time.
Unlike traditional dive tables (but on a similar basis as dive computers which accumulate gas loading based on summation of ingassing at current depth over short intervals - ratio deco sums over 5 minute intervals while computers may refine this to 30 second intervals or less), ratio deco is calculated by reference to average[clarification needed] depth rather than maximum depth. The technique also requires that the dive be divided into 5 minute segments, and the total decompression time accumulated for each 5 minute segment be calculated. To add an element of conservatism, divers lump 5 minute segments into pairs, and use the deeper depth of the pair to calculate the amount of decompression time accumulated.[citation needed]
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Ratio decompression AI simulator
(@Ratio decompression_simulator)
Ratio decompression
Ratio decompression (usually referred to in abbreviated form as ratio deco) is a technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer. It is generally taught as part of the "DIR" philosophy of diving promoted by organisations such Global Underwater Explorers (GUE) Innerspace Explorers (ISE) and Unified Team Diving (UTD) at the advanced technical diving level. It is designed for decompression diving executed deeper than standard recreational diving depth limits using trimix as a "bottom mix" breathing gas.
There have been three iterations of UTD Ratio Deco, The latest as of 2021 is RD 3.0, which has less emphasis on deep stops than RD 2.0.
The physiology behind the off-gassing of nitrogen or helium absorbed by the body from breathing gases under pressure has never been definitively established, particularly in relation to the formation of bubbles in the body's tissues, and a number of different algorithms have been developed over the years, based on simplified hypotheses of gas transport and absorption in body tissues, modified to fit empirical data, to predict the rate of off-gassing to reduce the risk of decompression sickness in divers to an acceptable level. However, these models do not describe the individual physiology of the diver accurately: divers have been known to suffer symptomatic decompression sickness whilst diving within the limits of dive tables or dive computers (sometimes referred to as an "undeserved hit"), and divers have exceeded No Decompression Limits but remained asymptomatic.
While Ratio Decompression is not a complete decompression model, it most resembles those of Bühlmann algorithm, and the Varying Permeability Model algorithm, with emphasis on the use of deep stops and gradient factors.[citation needed] It is a type of simplified curve fitting applied to a model decompression profile considered by the author of the model to be acceptable based on experience.
A conventional decompression profile, based on a dissolved gas model algorithm, will result in a diver ascending relatively quickly through shorter deep stops before spending a great deal of time at the shallower stops (resulting in a much sharper angle in the depth/time graph of the ascent profile), ratio deco will allow a diver to dynamically[clarification needed] take a total decompression obligation[clarification needed] for a given dive and create a profile which makes better use[clarification needed] the most effective parts[clarification needed] of the decompression profile, and spends comparatively less time at the less effective stops[clarification needed] (resulting in a much softer[clarification needed][weasel words] curve in the depth/time graph of the ascent profile).[citation needed]
The basis for calculating a decompression schedule using ratio decompression is actually relatively simple (and certainly much simpler than the extremely complicated algorithms used by dive computers). The following represents a slightly simplified summary of the process.[clarification needed] Not all versions of ratio deco use exactly the same procedure.
The starting point is to ascertain the correct ratio (from whence the technique gets its name) of the amount of total decompression time as a ratio to the total bottom time. This ratio is fixed solely by reference to depth. Although on traditional tables the amount of decompression would vary according to time at depth, the basis of the theory that most dives will operate within a range of normalcy[clarification needed] which makes the use of fixed ratios permissible.[clarification needed] Certain depths establish certain ratios; a 1:1 ratio occurs at approximately 150 feet (46 m); a 2:1 ratio occurs at approximately 220 feet (67 m). Between these depths, for each 10 feet (3 m) deeper or shallower than a fixed ratio depth, the diver will then add or subtract a specified number of minutes to their total decompression time.[citation needed] Accordingly, once the diver knows their planned depth and time, they can look up the most proximate ratio, calculate the difference in depths, and add or subtract the appropriate number of minutes from their total bottom time to give a total decompression time.
Unlike traditional dive tables (but on a similar basis as dive computers which accumulate gas loading based on summation of ingassing at current depth over short intervals - ratio deco sums over 5 minute intervals while computers may refine this to 30 second intervals or less), ratio deco is calculated by reference to average[clarification needed] depth rather than maximum depth. The technique also requires that the dive be divided into 5 minute segments, and the total decompression time accumulated for each 5 minute segment be calculated. To add an element of conservatism, divers lump 5 minute segments into pairs, and use the deeper depth of the pair to calculate the amount of decompression time accumulated.[citation needed]