blueabysss
Registered
Does anyone have any idea why the different scuba agencies do not us the US Navy tables? or why none of them are equal to each other? My theory is that they just want more money from the students. Any answers?
a standard dive table
- Thread starter blueabysss
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
SSI uses the Navy tables (subset).
NAUI uses the Navy tables for their advanced stuff (subset)
NOAA uses the Navy tables (subset).
NSS/CDS uses the Navy tables.
I think the YMCA uses the Navy tables (they did when I got my YMCA card in '71) Walter?
----------
Other agencies use other tables because they think they are better.
There's no money in tables.
Rick
NAUI uses the Navy tables for their advanced stuff (subset)
NOAA uses the Navy tables (subset).
NSS/CDS uses the Navy tables.
I think the YMCA uses the Navy tables (they did when I got my YMCA card in '71) Walter?
----------
Other agencies use other tables because they think they are better.
There's no money in tables.
Rick
Bob3
Contributor
NOAA did the development of the altitude & nitrox tables that were adopted by the Navy. Nice to see govt. agencies sharing.
Most (all?) of the agencies which originated in the US began using US Navy tables.
NAUI & YMCA use modified US Navy tables. They've backed off the NDL's various amounts.
YMCA will tell you they backed off the NDL's 2 letter groups, but that's not exactly the case, although what they did was very close. They backed off 2 letter groups for all depths except 100 ft. At 100 ft, they backed off 2 letter groups and 2 minutes. They then left the repetitive group as if they've backed off three letter groups. I don't know why, but I suspect it may be because backing off 2 letter groups at 100 ft would have left the NDL's at 100 ft and 90 ft identical and that would have seemed odd. Now this seems like an error on the side of caution, but in actuality for dives to 100 ft for 16 - 18 minutes, the YMCA tables are less conservative than the US Navy tables. Those times at that depth on the US Navy tables leave a diver in the F repetitive group. On the YMCA tables the diver is in the E repetitive group. Except for those three minutes at 100 ft, YMCA tables are the same or more conservative than US Navy tables. I have pointed this out to the YMCA SCUBA Program. They feel it is an insignificant difference.
NAUI tables are backed off 3 letter groups for 40 ft, 2 letter groups for 50 ft, and 1 letter groups for all other depths. NAUI also increased the time to clear the tables from 12 to 24 hours.
MEDA uses straight US Navy tables, but did make them harder to read.
PDIC uses straight US Navy tables in the exact same format as those published by Jeppesen.
DCIEM developed their own tables based on slightly different theory. The format is much more user friendly.
PADI switched from the US Navy tables to their own in the late 1980's. It may have been the result of several product liability lawsuits of the time. ABC news did a story on it in, I believe, their 20/20 program. I taped it, but I have not been able to find that tape. In my opinion, PADI got a raw deal on the program. ABC interviewed people who were bent while pushing the tables to the max (I was following the interview with tables in hand) and then asked PADI why they were bent while "well within the limits" of the tables. They also gave PADI a hard time for continuing to sell their version of the US Navy tables when their "newer safer" table was available. What struck me as odd was they accepted as a given that the newer table was, in fact, safer with no evidence to support the claim. If memory serves, the people interviewed in the program would have had longer bottom times had they been using the newer tables. Bottom line, don't push any table to its limits.
NAUI & YMCA use modified US Navy tables. They've backed off the NDL's various amounts.
YMCA will tell you they backed off the NDL's 2 letter groups, but that's not exactly the case, although what they did was very close. They backed off 2 letter groups for all depths except 100 ft. At 100 ft, they backed off 2 letter groups and 2 minutes. They then left the repetitive group as if they've backed off three letter groups. I don't know why, but I suspect it may be because backing off 2 letter groups at 100 ft would have left the NDL's at 100 ft and 90 ft identical and that would have seemed odd. Now this seems like an error on the side of caution, but in actuality for dives to 100 ft for 16 - 18 minutes, the YMCA tables are less conservative than the US Navy tables. Those times at that depth on the US Navy tables leave a diver in the F repetitive group. On the YMCA tables the diver is in the E repetitive group. Except for those three minutes at 100 ft, YMCA tables are the same or more conservative than US Navy tables. I have pointed this out to the YMCA SCUBA Program. They feel it is an insignificant difference.
NAUI tables are backed off 3 letter groups for 40 ft, 2 letter groups for 50 ft, and 1 letter groups for all other depths. NAUI also increased the time to clear the tables from 12 to 24 hours.
MEDA uses straight US Navy tables, but did make them harder to read.
PDIC uses straight US Navy tables in the exact same format as those published by Jeppesen.
DCIEM developed their own tables based on slightly different theory. The format is much more user friendly.
PADI switched from the US Navy tables to their own in the late 1980's. It may have been the result of several product liability lawsuits of the time. ABC news did a story on it in, I believe, their 20/20 program. I taped it, but I have not been able to find that tape. In my opinion, PADI got a raw deal on the program. ABC interviewed people who were bent while pushing the tables to the max (I was following the interview with tables in hand) and then asked PADI why they were bent while "well within the limits" of the tables. They also gave PADI a hard time for continuing to sell their version of the US Navy tables when their "newer safer" table was available. What struck me as odd was they accepted as a given that the newer table was, in fact, safer with no evidence to support the claim. If memory serves, the people interviewed in the program would have had longer bottom times had they been using the newer tables. Bottom line, don't push any table to its limits.
I can't find the tape from Provo, but I do have the 20/20 tape. It was 1988. And yes I do agree that PADI got a bad deal on it.
Wreck/Tec
Contributor
I was always under the impression the NAVY dive tables were geared towards an individual who was in optimum physical condition! Having said that, in the recreational/technical community, there are a diverse collection of physically fit and un fit people diving. This would lend me to believe that the tables wouldn't apply to all obviously, hense their modification for some of the agencys.
Wreck/Tec
Wreck/Tec
The navy designed their tables so a diver to drop to his marked depth and complete a job. Returning safely to the surface was a bonus. They got it as close to the edge as they could so they did not have to keep training new divers and still get the maximum amount of work out of their men. If you have ever been in the service you'll understand.
As stated above navy divers are usually in great shape and expendable. My two cents worth
Hallmac
As stated above navy divers are usually in great shape and expendable. My two cents worth
Hallmac
nradov
Guest
Any of the "no deco" air tables you can get from US Navy / PADI / NOAA / whoever are pretty much equally bad in that they are based around flawed understandings of how deco really works. But in the cases of those PADI divers who got bent did anyone check to see if they had undetected circulatory system shunts (like a PFO), or if they had been bounce diving ( http://www.wkpp.org/articles/Decompression/why_we_do_not_bounce_dive_after_diving.htm ). Those are the two most common root causes of "unearned hits".
-Nick
Dr Deco
Contributor
- Messages
- 2,384
- Reaction score
- 96
- # of dives
- I just don't log dives
Dear blueabyss:
This is long and one must read it all if it is to answer the question.
US Navy Tables
The US Navy Dive Tables were developed for decompression diving. In actuality, there was not any specific program to develop the No Decompression Limits since there are not required for hart had, surface supplied divers. These divers will virtually always stay down for whatever time is necessary to completed the task, and coming up to avoid decompression is simply not a requirement in a scenario where there is a dive team and surface decompression capabilities.
The US Navy tables (as well as those for any other naval service in the world or any commercial company) are designed for decompression diving. The system of repetitive groups was chosen by the US Navy to allow the calculation of residual gas in the body when planning the next dive. It is not the only system to allow for such planning. The Royal Navy uses a different system and does not have the same type of repetitive groups.
Repetitive Diving
To calculate a repetitive dive, it is necessary to know the amount of gas in that compartment which is filled to its greatest degree. One then follows the off gassing of that compartment. EACH POSSIBLE COMBINATION MUST BE ACCOUNTED FOR AND APPROPRIATE OFF GASSING TABLES PLACED IN THE DIVE MANUAL. Nothing will be simple since military and commercial tables will only consider decompression dives.
Another possibility is to consider maximal gas loading in the slowest half time compartment. This is appropriate since military tables are made for decompression diving. If the off gassing of only the slowest compartment is considered, all faster compartments will off load appropriately. This will not really be an optimal system unless you typically load the slowest compartment to a considerable extent. Since these are for decompression diving, the slowest compartment will usually play a role , at least near the end of the decompression.
Recreational SCUBA Diving
What if you are a recreational SCUBA diver and do not perform decompression dives? Why would you want to consider the off gassing of the slowest half time compartment? Is this not really a waste of time since it is barely loaded in virtually all cases, and is never a controlling tissue.
We now enter into the realm of recreational tables. These are no decompression dives and have short bottom times in comparison to commercial and military hardhat, surface supplied diving.
It is possible to simply recalculate the US Navy tables and change the controlling tissue for repetitive dives from 120 minute to something else (it turns out that 60 minutes is more appropriate). When Ray Rogers approached PADI with this idea, they liked the idea of the Recreational Diver Table, but did not want to see a pencil and paper modification. They wished to see a recalculation with new, reduced no-decompression limits and actual tests. Thus, the PADI Recreational Dive Planner was born.
Table Limits
No tables or decompression meters will take you to the edge of the bends/no bends limit because it does not exist. There is a gradual change. It is much like nightfall; there is not a minute where it is light and then dark the next moment. Only in space on the Space Station, with no atmosphere and a speed of 18,00 miles an hour, does it go from night to day in a flash.
Dr Deco :doctor:
This is long and one must read it all if it is to answer the question.
US Navy Tables
The US Navy Dive Tables were developed for decompression diving. In actuality, there was not any specific program to develop the No Decompression Limits since there are not required for hart had, surface supplied divers. These divers will virtually always stay down for whatever time is necessary to completed the task, and coming up to avoid decompression is simply not a requirement in a scenario where there is a dive team and surface decompression capabilities.
The US Navy tables (as well as those for any other naval service in the world or any commercial company) are designed for decompression diving. The system of repetitive groups was chosen by the US Navy to allow the calculation of residual gas in the body when planning the next dive. It is not the only system to allow for such planning. The Royal Navy uses a different system and does not have the same type of repetitive groups.
Repetitive Diving
To calculate a repetitive dive, it is necessary to know the amount of gas in that compartment which is filled to its greatest degree. One then follows the off gassing of that compartment. EACH POSSIBLE COMBINATION MUST BE ACCOUNTED FOR AND APPROPRIATE OFF GASSING TABLES PLACED IN THE DIVE MANUAL. Nothing will be simple since military and commercial tables will only consider decompression dives.
Another possibility is to consider maximal gas loading in the slowest half time compartment. This is appropriate since military tables are made for decompression diving. If the off gassing of only the slowest compartment is considered, all faster compartments will off load appropriately. This will not really be an optimal system unless you typically load the slowest compartment to a considerable extent. Since these are for decompression diving, the slowest compartment will usually play a role , at least near the end of the decompression.
Recreational SCUBA Diving
What if you are a recreational SCUBA diver and do not perform decompression dives? Why would you want to consider the off gassing of the slowest half time compartment? Is this not really a waste of time since it is barely loaded in virtually all cases, and is never a controlling tissue.
We now enter into the realm of recreational tables. These are no decompression dives and have short bottom times in comparison to commercial and military hardhat, surface supplied diving.
It is possible to simply recalculate the US Navy tables and change the controlling tissue for repetitive dives from 120 minute to something else (it turns out that 60 minutes is more appropriate). When Ray Rogers approached PADI with this idea, they liked the idea of the Recreational Diver Table, but did not want to see a pencil and paper modification. They wished to see a recalculation with new, reduced no-decompression limits and actual tests. Thus, the PADI Recreational Dive Planner was born.
Table Limits
No tables or decompression meters will take you to the edge of the bends/no bends limit because it does not exist. There is a gradual change. It is much like nightfall; there is not a minute where it is light and then dark the next moment. Only in space on the Space Station, with no atmosphere and a speed of 18,00 miles an hour, does it go from night to day in a flash.
Dr Deco :doctor:
Dr Deco
Contributor
- Messages
- 2,384
- Reaction score
- 96
- # of dives
- I just don't log dives
Dear nradov:
Ouch!
I must take exception to the comment that the US Navy/PADI/NOAA tables are equally bad since they are based around flawed understandings of how deco works. I have worked with these people on a professional level since 1969, and I will assure you that they are well aware of how decompression works, at least on a functional level. They also know how to construct tables for a wide variety of situations. There is no question that I debate them on many of their concepts, but they can produce decompression tables for a variety of situations.
WKPP Diving
These are quite specific dive situations, and the methods would probably not work well in all situations (walking around and hauling dive gear).
PFO and Undeserved Hits
The PFO situation is only applicable to neurological decompression sickness. It does NOT APPLY to pain only decompression sickness (the bends). The Bends is not an embolic phenomenon, and those that maintain otherwise are misinformed about their diving physiology. This aspect has been debated for more than 60 years and was a dead issue long before I entered the field.
Undeserved Hits
When these are pain-only DCS, they are most likely the result of bad gas exchange or creation of micronuclei. To this we might add dehydration (surface tension changes) and yet-unknown biochemical variations of the body. All of this can be mitigated by not generating nuclei and not producing a bad asymmetry in the uptake and elimination process.
PADI divers or any other ones are sometimes check for a PFO but never for a case of joint pain DCS. This has a localized gas bubble etiology and not the result of an infarct (= embolization).
Dr Deco :doctor:
Ouch!
I must take exception to the comment that the US Navy/PADI/NOAA tables are equally bad since they are based around flawed understandings of how deco works. I have worked with these people on a professional level since 1969, and I will assure you that they are well aware of how decompression works, at least on a functional level. They also know how to construct tables for a wide variety of situations. There is no question that I debate them on many of their concepts, but they can produce decompression tables for a variety of situations.
WKPP Diving
These are quite specific dive situations, and the methods would probably not work well in all situations (walking around and hauling dive gear).
PFO and Undeserved Hits
The PFO situation is only applicable to neurological decompression sickness. It does NOT APPLY to pain only decompression sickness (the bends). The Bends is not an embolic phenomenon, and those that maintain otherwise are misinformed about their diving physiology. This aspect has been debated for more than 60 years and was a dead issue long before I entered the field.
Undeserved Hits
When these are pain-only DCS, they are most likely the result of bad gas exchange or creation of micronuclei. To this we might add dehydration (surface tension changes) and yet-unknown biochemical variations of the body. All of this can be mitigated by not generating nuclei and not producing a bad asymmetry in the uptake and elimination process.
PADI divers or any other ones are sometimes check for a PFO but never for a case of joint pain DCS. This has a localized gas bubble etiology and not the result of an infarct (= embolization).
Dr Deco :doctor:
Similar threads
