Decompression Tables

[Shearwater]

Although I don't have any inside information about what the Navy does or doesn't do, I would like to correct a few of the obvious mistakes about Navy decompression.

Although the Navy tables have been around a long time, they were updated this year to use oxygen from 20 feet up. The Navy does use the Navy tables, but the adjustment to use oxygen from 20 feet says to me that they have determined that they were too aggressive, particularly on longer and deeper exposures.

The Navy likely doesn't use any commercial dive program widely. If they wanted to use a bubble model, they would likely use VVAL-18, not VPM. However they appear to be a lot less enthusiastic about bubble models than some researchers have been in the past.

The Navy tables don't have a 5% bend rate. Intuitively it is impossible to believe that the Navy bends their personnel on one out of twenty dives!

This is all public information if you attend the DAN and UHMS conferences where various navies are active participants. The Navy is very active in diving research. I think it would be safe to say that using probabalistic models, based on empirical data, to calibrate their tables is the state of the art of Navy decompression procedures.

Unfortunately, these models will probably be out of reach of current wrist computers for some years to come.

Bruce

 

[HowardE]

Bruce,

According to a mutual friend of ours.

a) The USN is using VPM.
2) If the USN Tables are pushed to the limits... yes - 5% bend rate. That includes the following caveat. If you are not ascending at 1 foot per second. You are off the table.


Yeah the navy tables have been around for a long time, and now they are updated to include Oxygen Decompression. The navy also currently has dive tables for in water and the combination of wet and dry decompression in a chamber. Most of us don't have that luxury.

Do you Bruce @ Shearwater think that relying on the OLD US Navy tables or the old NAUI tables is a prudent approach to a decompression dive? Which some people have stated because, "that's what I learned on 30 years ago".

 

[captain]

Bruce,

According to a mutual friend of ours.


Do you Bruce @ Shearwater think that relying on the OLD US Navy tables or the old NAUI tables is a prudent approach to a decompression dive? Which some people have stated because, "that's what I learned on 30 years ago".

I didn't say and from what I have read neither has anyone else said they were doing "mandatory stop" decompression dives using the old Navy tables.

The OP's question was what table do you use to backup your computer and are the tables you use based on the same model as the computer.
You guys doing deep decompression stop dives always seem to ridicule the NDL divers who aren't diving your profiles about using tables other than what you believe is best.

There is an NEDU presence on this board, perhaps try getting the straight answer from them before making comments.

 

[HowardE]

You guys doing deep decompression stop dives always seem to ridicule the NDL divers who aren't diving your profiles about using tables other than what you believe is best.

I never criticized NDL divers or diving. More of my diving is NDL diving than anything else. Re-read my post? I just explained 2 very different points, without criticizing NDL type recreational divers.

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[scjoe]

This 5% figure that keeps getting thrown around is pure urban legend.

 

[captain]

I never criticized NDL divers or diving. More of my diving is NDL diving than anything else. Re-read my post? I just explained 2 very different points, without criticizing NDL type recreational divers.

Posted via Mobile Device

Howard, this wasn't aimed at you in particular. It was a general statement as I perceive the issue.
But you did ask a companion if relying on the OLD US Navy tables or the old NAUI tables is a prudent approach to a "decompression dive"
I assume by decompression dive you mean you meant a dive requiring mandatory stops.
I don't want to get into the "every dive is a decompression dive". We both know that it is true but in varying degrees.

 

[Shearwater]

Bruce,

According to a mutual friend of ours.

a) The USN is using VPM.
2) If the USN Tables are pushed to the limits... yes - 5% bend rate. That includes the following caveat. If you are not ascending at 1 foot per second. You are off the table.


Yeah the navy tables have been around for a long time, and now they are updated to include Oxygen Decompression. The navy also currently has dive tables for in water and the combination of wet and dry decompression in a chamber. Most of us don't have that luxury.

Do you Bruce @ Shearwater think that relying on the OLD US Navy tables or the old NAUI tables is a prudent approach to a decompression dive? Which some people have stated because, "that's what I learned on 30 years ago".

Hi Howard,

I certainly can't prove they aren't using VPM anywhere. It's a big organization. But I have been to quite a few presentations over the last few years and they have never mentioned it. They have talked lots about bubble models, and they talked about VVAL 18 and others explicitly, but even those were experimental.

I think the Navy dives the Navy tables as specified in NAVSEA 00C, Supervisor of Salvage and Diving, U.S. Navy Diving Manual.

As to the 5% bend rate: They actually brought up that rumor at the last UHMS meeting in Las Vegas and discounted it. You will not convince me that they have a bent diver every 20th dive.

Would I use the old tables for modern decompression diving - no. With oxygen from 20 feet according to the new tables - no problem. The new tables match the DCIEM tables quite closely, and most divers would call the DCIEM tables very conservative.

I think there is general agreement that the data that was used in earlier decompression science came from shallower dives and it doesn't extrapolate well to the deeper and longer dives we are doing now.

So to answer your question, in a long-winded way, I agree with you. I don't think the OLD Navy tables would be appropriate for decompression diving now.

Bruce

 

[syntaxerrorsix]

This 5% figure that keeps getting thrown around is pure urban legend.

The exact number may in fact be legend however, Navy divers assume a greater risk of DCS as they can be treated immediately. It's easier to bend the diver and fix them on the go rather than sit in potentially hostile waters waiting from them to complete their stops.

The Navy prepares for war, not necessarily the best diving practices. This is why it is unwise to base civilian dive practices off their practices.

 

[DCBC]

Hi Howard,

Would I use the old tables for modern decompression diving - no. With oxygen from 20 feet according to the new tables - no problem. The new tables match the DCIEM tables quite closely, and most divers would call the DCIEM tables very conservative.

I was a research diver attached to DCIEM involved in the development of the DCIEM tables (sport tables) and later the Heliox tables that replaced the US Navy partial pressure tables for operational mixed gas diving to 100 M.

Shearwater you're correct in saying that these are very conservative. They do however offer the safest options available. By comparison, on a initial NDD to 100 ft, DCIEM allows a BT of 15 mins, USN (1956) of 25 mins, USN (1993) 27 mins and USN (1999) 25 mins.

 

[boulderjohn]

A
DCS
Dr. Richard Moon's paper "Evaluation of a Method for Reducing Decompression Sickness (DCS) during Recreational Diving" (2009) states that in a dataset provided by DAN, in 52,168 recreational air dives, there were 23 DCS incidents (using dive computers). That's approx. 1 incident of DCS in every 2200 dives for dives using a computer.

Given the total number of dives claimed by the members on this site, if this information is reliable, almost everyone will have experienced DCS at least once... I point this out because the the incidence rate is in-fact much higher than one might like to think.

That is not an accurate use of statistics. For your conclusion to be true, every diver would have to dive 2,200 dives, and every dive would have to have an equal risk for DCS.

In reality, some divers are very aggressive and push the limits regularly. These divers should have a much higher incidence of DCS than the rest of the population that dives more conservatively. At the other extreme, many divers stay almost exclusively in places like the reefs at Key Largo, where it is just about impossible to be bent.

If the familiar 80/20 rule has any bearing, then we might expect 80% of the DCS hits to occur among 20% of the diving population. Given the actual number of dives people take and the fact that most do not push the limits, it would not surprise me to learn that more than 90% of the population will never experience DCS.