lekrigbaum
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What is the source for the Recreational Dive Tables? Are the PADI, NAUI, SDI, etc tables all different or is there a common source for those tables? Thanks for any info.
Source for Rec Dive Tables?
- Thread starter lekrigbaum
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DevonDiver
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Most agencies utilise Doppler-Modified US Navy tables. You can get these via an online search, as they are 'open source'. PADI designed its own tables, which offer some benefits for shorter surface intervals and longer NDLs for repetitive dives.
The Chairman
Chairman of the Board
There is no one single source, but most have their roots in the Navy Dive Tables.
A common misconception is that PDCs (Personal Dive Computers) have their roots in the tables, which is simply not true. All tables and PDCs are based on algorithms derived from various decompression models. Some are more conservative than others.
A common misconception is that PDCs (Personal Dive Computers) have their roots in the tables, which is simply not true. All tables and PDCs are based on algorithms derived from various decompression models. Some are more conservative than others.
Try this link: NOAA No Deco Air
All tables use a fairly similar mathematical underpinning. They assume the body is divided into "compartments", each of which loads and unloads nitrogen at a defined rate. They also make assumptions about the maximum nitrogen tension each compartment can tolerate before bubbling. Most models assume the compartments load and unload independently of one another, but I believe there is one that assumes that they load serially.
The reason the tables come up with different numbers is the differences in the number of compartments, the half-lives of the specific compartments they use, and the differences in the assumed maximum tensions. But the mechanics of the mathematics are essentially the same.
Tables of all flavors are subjected to some degree of validation, but the amount of validation varies.
A good book to read about all this is Mark Powells Deco for Divers, or Lippmann and Mitchell's Deeper into Diving. You can also find Erik Baker's papers, "Understanding M-values", and "Clearing up the Confusion about Deep Stops" in various locations on line.
The reason the tables come up with different numbers is the differences in the number of compartments, the half-lives of the specific compartments they use, and the differences in the assumed maximum tensions. But the mechanics of the mathematics are essentially the same.
Tables of all flavors are subjected to some degree of validation, but the amount of validation varies.
A good book to read about all this is Mark Powells Deco for Divers, or Lippmann and Mitchell's Deeper into Diving. You can also find Erik Baker's papers, "Understanding M-values", and "Clearing up the Confusion about Deep Stops" in various locations on line.
Mr Carcharodon
Contributor
The first modern diving table was developed by the Scottish physiologist J. S. Haldane and adopted by the Royal Navy in 1908. Haldane’s tables were used through the early 1960’s. Haldane developed his tables based on studies of animal subjects that were exposed to various pressures and times and then examined for signs of decompression illness. Based on these experimental trials Haldane developed a theory that decompression sickness could be avoided if dissolved gas pressure is keep to less than twice ambient pressure.
The work for the sixty or so years after Haldane were largely refinements of Haldane’s work. Refinements included adjustments for longer and deeper dives; collection of data on human subjects, and dive tables for gases other than air.
PADI and DSAT developed a new set of tables in the 1980’s to support recreational diving. The feeling at the time was that the US Navy tables were not conservative enough for the population of recreational divers. That was because the Navy tolerated a fairly high bends rate of 1-2%. They tolerated this rate in part because they had facilities to immediately treat bent divers. Also Navy divers were generally considered to be less predisposed to DCS because they were younger and fitter the general diving population. And working Navy dives had different depth/time profiles that were typical for recreational dives. DSAT reduced the allowable tissue pressures relative to the Navy tables and used a faster tissue compartment to control the dives. DSAT did extensive validation on their tables on human subjects in hyperbaric chambers and in the water. They also used Doppler bubble scores to assure consistency across different depth/time pairs. The DSAT tables have proven to be safe for the general diving population. So much so that DCS is a pretty rare cause of death in diving compared to drowning, embolism or cardiac events. Also I would be remiss if I did not point out that Michael Powell, “Dr. Deco” here on Scubaboard, was directly involved in the DSAT work.
NAUI published a set of tables in 2002 based on RGBM (reduced gradient bubble model). RGBM sets dive limits based on an assumed maximum tolerated number or volume of bubbles. RGBM arrives at a volume by integrating pressure gradient v. time with extra squiggles and jots thrown in for good measure. It is interesting to note that there is considerable overlap between RGBM and the Haldanian models in that in both cases pressure gradient is used as a control. But the bubble models (of which VPM is another) are more general and can be applied to more unique situations than the Haldanian models. Of course a lot of the generality is lost once the model is distilled enough to make a table.
Baker's papers at decompession.org are a good place to start. As is Haldane's 1908 paper at Rubicon Research.
The work for the sixty or so years after Haldane were largely refinements of Haldane’s work. Refinements included adjustments for longer and deeper dives; collection of data on human subjects, and dive tables for gases other than air.
PADI and DSAT developed a new set of tables in the 1980’s to support recreational diving. The feeling at the time was that the US Navy tables were not conservative enough for the population of recreational divers. That was because the Navy tolerated a fairly high bends rate of 1-2%. They tolerated this rate in part because they had facilities to immediately treat bent divers. Also Navy divers were generally considered to be less predisposed to DCS because they were younger and fitter the general diving population. And working Navy dives had different depth/time profiles that were typical for recreational dives. DSAT reduced the allowable tissue pressures relative to the Navy tables and used a faster tissue compartment to control the dives. DSAT did extensive validation on their tables on human subjects in hyperbaric chambers and in the water. They also used Doppler bubble scores to assure consistency across different depth/time pairs. The DSAT tables have proven to be safe for the general diving population. So much so that DCS is a pretty rare cause of death in diving compared to drowning, embolism or cardiac events. Also I would be remiss if I did not point out that Michael Powell, “Dr. Deco” here on Scubaboard, was directly involved in the DSAT work.
NAUI published a set of tables in 2002 based on RGBM (reduced gradient bubble model). RGBM sets dive limits based on an assumed maximum tolerated number or volume of bubbles. RGBM arrives at a volume by integrating pressure gradient v. time with extra squiggles and jots thrown in for good measure. It is interesting to note that there is considerable overlap between RGBM and the Haldanian models in that in both cases pressure gradient is used as a control. But the bubble models (of which VPM is another) are more general and can be applied to more unique situations than the Haldanian models. Of course a lot of the generality is lost once the model is distilled enough to make a table.
Baker's papers at decompession.org are a good place to start. As is Haldane's 1908 paper at Rubicon Research.
DaleC
Contributor
In the 1960-1970's the Canadian military developed their own set of tables (DCIEM) which are, I believe (could be corrected) based on the most comprehensive depth tested research to date. They are conservative and have a far less acceptable rate of DCS risk associated with them than say, the old US navy tables.
When using the US tables one has to keep in mind that there was (for navy divers) a fairly high acceptable rate of DCS as they had chambers on board their vessels for rapid treatment. That may not be the same risk an isolated diver would find acceptable.
When using the US tables one has to keep in mind that there was (for navy divers) a fairly high acceptable rate of DCS as they had chambers on board their vessels for rapid treatment. That may not be the same risk an isolated diver would find acceptable.
Another thing to keep in mind is that most military-originating tables were cut with the average military diver in mind (and that's who they tested). You can read that as, "divers in excellent physical shape". My 30 year old civilian software engineer's body is going to decompress a bit differently than a 22 year old diver in combat-ready condition.
scjoe
Contributor
I don’t know where the idea that the Navy has a 1-2% bend rate comes from.
According to a piece published around 2001 by Larry Taylor who was then the Dive Safety Coordinator at the University of Michigan, from 1990-1995 there were 382 reported cases of DCS in 648,488 dives logged by the Navy. He cited as his source of this information a US Naval Safety Center report published in 1997. If my math is correct that is a 0.06% accident rate.
In the hands of scientific divers, the rate is even lower. James Stewart was the dive safety officer at Scripps from 1960 to 1991. Scripps used the Navy Tables during that period. In writing about the use of the Navy Dive Tables, he once stated, “The Scripps program has over 200,000 cumulative dives since the early 1950s. We have had only a single case of decompression sickness.”
According to a piece published around 2001 by Larry Taylor who was then the Dive Safety Coordinator at the University of Michigan, from 1990-1995 there were 382 reported cases of DCS in 648,488 dives logged by the Navy. He cited as his source of this information a US Naval Safety Center report published in 1997. If my math is correct that is a 0.06% accident rate.
In the hands of scientific divers, the rate is even lower. James Stewart was the dive safety officer at Scripps from 1960 to 1991. Scripps used the Navy Tables during that period. In writing about the use of the Navy Dive Tables, he once stated, “The Scripps program has over 200,000 cumulative dives since the early 1950s. We have had only a single case of decompression sickness.”
Mr Carcharodon
Contributor
It comes from Workman's 1965 paper: CALCULATION OF DECOMPRESSION SCHEDULES FOR NITROGEN-OXYGEN AND HELIUM-OXYGEN DIVES, NAVY EXPERIMENTAL DIVING UNIT WASHINGTON D C
Workman, RD. Captain Workman was a medical officer assigned to the Navy Experimental Diving Unit. "Tolerated" 2% is a key, which is to say that was the expected bends rate for dives to the limits of those tables. If Scripps did lots of dives to 30 fsw and got no bends that is hardly surprising.
You can download it at Rubicon.
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