which dive tables?

[maged_mmh]

So, from all the above, let's say that most do not trust tables for multiple dives (whether PADI or else)??

 

[Walter]

So, from all the above, let's say that most do not trust tables for multiple dives (whether PADI or else)??

I don't know about most, but I trust the more conservative versions of the US Navy tables, YMCA, NAUI, etc.

 

[jeckyll]

I don't know about most, but I trust the more conservative versions of the US Navy tables, YMCA, NAUI, etc.

I don't have nearly the experience of some of the folks who've posted in the thread, but I try not to get to max out the tables and use longer SI's than I'd "need" to to do my 2nd dive.

I also do more stops, especially on deeper dives and try to turn those dives into multi level dives with significant time spent shallow.

In addition, I use a rather conservative computer which I've turned up the conservatism on from default ...

I try to do a light cardio workout between 4 -> 24 hours pre diving and to stay hydrated. I do shallow / single dives if I've been having much stress in my life and I do slow ascents on all dives.

For me, I'm hoping that by doing more than just not diving the tables / diving the computer to the 'edge' and focusing on some of the other areas, I'm reducing the chances of DCS a little bit every time.

I guess only time will tell

Bjorn

 

[Walter]

Excellent advice, Bjorn.

 

[Charlie99]

On the RDP I have a problem with special rules regarding minimum surface intervals for divers in the x,y, and z pressure groups. I have seen far too many DM candidates miss the questions regarding these rules on test to believe that "Joe vacation diver" who surprisingly is trying to do the right thing and actually looks at a table would have any chance at all to get it right.

Have you actually looked at what dives it takes to get yourself into a condition where the WXYZ rules apply? They only apply when doing 3 or more dives per day, and then only if you are doing unusually long, shallow dives.

The way the PADI RDP differs from the US Navy derived tables (pre-RGBM NAUI, YMCA, SSI, and many others) is that the controlling compartment for repetitive diving is assumed to be the 60 minute compartment on the RDP, while the USN/NAUI/YMCA/SSI tables use the 2 hour compartment. This is the reason that the PADI RDP appears so liberal on repetitive dives when Walter compares the RDP to his preferred YMCA tables. OTOH, if you compare repetitive dives on the PADI RDP to the output of the many different decompression programs you will see that they are even more liberal on repetitive dives than the PADI RDP. This is because for square profile dives deeper than about 50', the controlling compartment is faster than 60 minutes and you offgas faster than the 60 minutes assumed by the PADI RDP, and waaay faster than the 2 hour halftime assumed by the USN-derived tables.

The WXYZ rules are only invoked for 3 or more dives in a day where you reach pressure group W or higher on one of the dives. This will happen only for very long shallow dives that are much longer than typical recreational scuba dives.

A couple examples --- getting to W or X requires a 1 hour min SI if doing 3 dives. Most people will be doing that if they are doing the dives needed to get out to W ---- 54 minutes at 60' or 71 minutes at 40'. If you are deeper than 60' then you can't even get to W and stay on the table. The 3 hour SI required by reaching Y or Z during a 3 dive sequence can only be reached on the RDP when the max depth is 40' or shallower. These unusually long, shallow dives are where the controlling compartment is a longer halftime than 60 minutes and the ad hoc rules are required. The tradeoff is that the RDP repetitive dive calculations are closer, but still more conservative, than what you would get from a decompression program or a computer.

OTOH, the USN/NAUI/YMCA/SSI tables always assume that the 2 hour compartment is the controlling one for repetitive dives and therefore come up with unecessarily conservative results on repetitive dives.

Charlie Allen

 

[Gene_Hobbs]

I hate to dig up an old thread but it has taken time to get the work done.

All tables are conservative in that they will protect all but the most sensitive diver on his worst day. The PADI RDP was tested in both a hyperbaric chamber, in the open water, and in a multiday trial. All of these were done using a Doppler bubble detector. The methods and results were presented at scientific meetings and the references are below. I was the individual (MRP) in charge of the test program.

This is being posted PRE-Press release but PADI/ DSAT has allowed us to include four papers in the Rubicon Research Repository. I still need to type the abstracts but the papers themselves are available now. Two papers mentioned early in this thread are:

Development and validation of no-stop decompression procedures for recreational diving: the DSAT recreational dive planner.
Hamilton, Rogers, and Powell. 1994
RRR ID: 4228

Doppler ultrasound monitoring of the gas phase formation following decompression in repetitive dives.
Powell, Spencer, and Rogers. 1988
RRR ID: 4229

 

[Dr Deco]

Hello readers:

Tables

My thanks to Gene Hobbs for the access to the book on laboratory results for the PADI RDP. This is, along with DCIEM, the most extensively tested set of tables for recreational divers made to date. They are the only tables tested – with Doppler - for multiple dives over multiple days.


Conservative

It takes little effort to take a tested table and create a more conservative table. What is tricky is to take a good table and make it more liberal and still be safe. That cannot be done by juggling a few numbers. It requires testing, and this is expensive. PADI did this.

Computers

Computers dive to the “model limits” on every dive. Unless you put it in, there is no “rounding” to the next deepest level and next longest time interval as is generally the case with tables. Many who dive with computers do not seem to recognize this.

Dr Deco :doctor:


The next class in Decompression Physiology for 2007 is August 18-19. :1book:
This class is at the USC campus in Los Angeles.
http://wrigley.usc.edu/hyperbaric/advdeco.htm