Navy Decompression Tables

[SurfLung]

- I recently read a neat article in the Historical Diving Society magazine about a Navy Hard Hat Diver who was salvaging a crashed bomber in shark infested waters. I got a sense for how routinely the Navy divers did long drawn out stage decompression dives.
- They were working divers and had to stay down long enough to perform significant tasks. Then as they came up, they would sit on a platform waiting out their decompression times and moving up to the next stage for more waiting. Air consumption wasn't an issue because they were fed unlimited air from the surface.
- When you think of it this way, those Navy decompression tables must have got a lot of real life trial and error testing... Not just theory. Is there any history on just how reliable those Navy Tables have turned out to be over the years?

[luis]

From my discussion with ex-salvage navy divers they tended to pad them whenever they actually did any stage decompression dives. For any kind of operations where they are actually doing stage decompression dives the Navy keeps a deco chamber on site.

I have read publish data on DCS hits and the acceptable DCS hits for commercial divers and Navy divers is much higher than recreational divers could tolerate. They have chamber on site during diving operations and any DCS hits are normally resolved by recompression treatment right away.

If you are really interested I can try to locate the source of the data, but I have reading several books and articles about decompression so I can’t remember where I saw it exactly.

I can’t remember the number of DCS hits, but it was interesting that the numbers for commercial divers was about twice as much as for the Navy divers. But in either case was way too frequent if you don’t have a deco chamber on site.

The Navy has newer algorithms and software.


If you are interested on doing any decompression dives I would recommend using V-planner, after you understand all the risks (and learn how to mitigate them). All dives are decompression dives, but when you have a stage decompression obligation, you in essence have an overhead environment (normally considered a soft overhead environment).

I would also recommend a class on deco procedures.

[swimjim]

I also recommend V-Planner. I use it myself and it is an excellent program. You can set the conservancy to basically old fart, which we both qualify for. LOL

Jim

[SurfLung]

- Ohh-Kay... I should download V-Planner and then look for a menu selection "OF".
- Very enlightening information about the Navy and Commercial divers tolerance for DCS. Their attitude sounds downright CASUAL. But I suppose the combination of working with it every day and the added confidence of having a decompression chamber handy would contribute to that. Still, pretty tough characters to live like that. And, those dive tables got a serious field test through them.
- My LDS is supposed to have me signed up for the next deep diving PADI certification class... Is that what I should take? I'm not planning to do stage decompression dives but I'd like to understand it better so I can use my dive computer more knowledgably. I've studied the SUUNTO "Reduced Gradient Bubble Model" RGBM information as well as a history of how decompression tables came about... Jim might have sent some of the links to me when I asked him about this stuff awhile back (I already have the V-Planner he recommended).

[JAdair]

Skip the PADI course.

Go to GUE.com and buy their DVD:
The Mysterious Malady: Toward an Understanding of Decompression Injuries

There is no DIR preaching, just interviews with the top minds in Decompression theory and practice.

Then buy Bennett & Elliott's Physiology and Medicine of Diving. Read it and at that point you will be better informed on Decompression theory than 99% of the instructors out there teaching it.

[SurfLung]

Skip the PADI course.

Go to GUE.com and buy their DVD:
The Mysterious Malady: Toward an Understanding of Decompression Injuries

There is no DIR preaching, just interviews with the top minds in Decompression theory and practice.

Then buy Bennett & Elliott's Physiology and Medicine of Diving. Read it and at that point you will be better informed on Decompression theory than 99% of the instructors out there teaching it.

- Thanks for the references. I just ordered the DVD a few minutes ago.

- I looked up DIR (Do It Right) diving on Wikipedia. Gotta say it starts out sounding fine but it sure goes on and on. The page followed on with DIW (Doing it Wrong) diving and a long, long list of what DIR says NOT to do.

- For now I will anxiously wait for delivery of my DVD. If I can handle that okay, I looking forward to curling up with the good Physiology book for some light reading...

- All kidding aside, thanks for the information and sources JADair, Luis, and SwimJim. I appreciate it.

[luis]

-
- Very enlightening information about the Navy and Commercial divers tolerance for DCS. Their attitude sounds downright CASUAL

No they do not take DCS casual at all. I am sorry if my post was a bit misleading in this respect. They take DCS very seriously. That is why they always have a deco chamber on site and as a minimum a hyperbaric medical technician on site during dive operations that require any stage deco.

I wish that I could remember the rate of DCS, but I don’t even want to guess. Some may consider it a small percentage, but I certainly didn’t. The odds did not seem too bad if you have a chamber on hand and a means of resolving the DCS, but IMO it was not an acceptable risk level for a recreational diver.



If you are interest about decompression theory and practice, the best general book I have found is Deco for Divers by Mark Powel.
http://www.amazon.com/Deco-Divers-Mark- ... 1905492073

http://www.dive-tech.co.uk/deco%20for%20divers.htm

It is an easy reading book (as easy reading as a technical book can be) and it is very up to date. I highly recommend it.


The PADI deep diving class is probably going to be kind of basic, but depending on the instructor may not be bad.

Skip the PADI course.

Go to GUE.com and buy their DVD:
The Mysterious Malady: Toward an Understanding of Decompression Injuries

There is no DIR preaching, just interviews with the top minds in Decompression theory and practice.

Then buy Bennett & Elliott's Physiology and Medicine of Diving. Read it and at that point you will be better informed on Decompression theory than 99% of the instructors out there teaching it.

Thanks for the recommendations.

I may have to get the DVD. In general, I do not subscribe to the DIR doctrine, but IMHO they do have many aspects that have a lot of value and I am always willing to learn if their valuable information.

This book looks good, but at $180 ($156 used); I am going to have to put it in my wish list. It also looks that the most recent edition (5 edition) is 10 years old. I am sure that it is still a great book, but I am going to wait.
http://www.amazon.com/Bennett-Elliotts- ... +of+Diving

Actually, after looking into it further, this book may be a bit more than what I am willing to spend time reading, but I am sure that it would be a good reference.


Thanks

[SurfLung]

IMO it was not an acceptable risk level for a recreational diver.

- I certainly agree... "Casual" was probably a poor choice of word. They could more easily afford to make a mistake with the presence of a deco chamber and doctor present... And so maybe they were more inclined to accept risks?
- Thanks for the additional references, Luis.

[Gilldiver]

One thing to consider when talking about Navy and commercial diving is if they are doing deco dives there will be a chamber on site. The Navy will usually pull a diver out when their 30’ stop is complete, get them on deck, strip them of most of the gear, then put them in the chamber and press them back down to 30’. The goal is to do that in less than 5 minutes. This is partly due to the desire to get the diver out of the water into a controlled situation as soon as possible, and the 20 & 10’ stops tend to be the longest part of any dive, and partly practical when using a diving stage. If the dive is at sea, at any depth above 30’ the stage and dive will be likely to be bashed into the hull if there is any type of sea running and the ship is rolling, so keeping the dive in the water at 20 & 10’ can actually more dangerous than pulling them up. It also allows the dive master to get another diver back to the job quickly by cleaning the stage etc.

For a look at early hard hat diving, get a copy of Edward Ellsberg’s book “On The Bottom” which is about the Salvage of the submarine USS S-51 off of Block Island, RI, which is my diving neighborhood.

[eskimo3883]

As I understand it the Navy tables and limits used at least up to the late 1970s were based on diagnosing decompression illness. Those observations were pretty much based on pain. The new analytical methods that can observe even small bubbles inside human subjects have now pointed out bubble formation can happen without any outward sign of an issue. I am thinking of a good coverage within a deep diving book by Gilliam. Pretty sure i screwed up the spelling of the name.

[SurfLung]

One thing to consider when talking about Navy and commercial diving is if they are doing deco dives there will be a chamber on site. The Navy will usually pull a diver out when their 30’ stop is complete, get them on deck, strip them of most of the gear, then put them in the chamber and press them back down to 30’. The goal is to do that in less than 5 minutes. This is partly due to the desire to get the diver out of the water into a controlled situation as soon as possible, and the 20 & 10’ stops tend to be the longest part of any dive, and partly practical when using a diving stage. If the dive is at sea, at any depth above 30’ the stage and dive will be likely to be bashed into the hull if there is any type of sea running and the ship is rolling, so keeping the dive in the water at 20 & 10’ can actually more dangerous than pulling them up. It also allows the dive master to get another diver back to the job quickly by cleaning the stage etc.

- That's really fascinating... Thanks for telling about it.