fine print in diving table, or can you do >3 dives on tables

[el-ninio]

do any of you know what the "fine print" in stand dive tables is? specifically, I'm interested to know which of the folowing is required for the table to pruduce accurate information

a) each dive must be shalower then the prvios one (during one dive day)

b) no more then two dives can be computed safly. (during one dive day)

c) entering a dive less then (10,30,60) min. after the last dive should be considered as part of the previos dive (or conpleatly avoded)


I have, in the past, been told that each of the above is true, but I no longer trust any of that information. Do any of you know if there are true and for which tables?

(I know that each of the above will increase the chance of DC - I myself rarely use tables and prefer to stick to my vyper.)


onother related questoin is with the "repetative dive grop" or "letters" common on most classical dive tables. Is there someone here that knows how there groups where made, and what they stand for? I have knolage about deco theory - that's again not the question - I'm interested in the relationship between decompression algorithems and table building.

thanks.

 

[mwilding]

I am no expert, but "b" is way off base

 

[pipedope]

My NAUI table do not have the same fine print.
The even have a handy worksheet that has space for three (3) dives.

 

[Saturation]

el-ninio once bubbled...
do any of you know what the "fine print" in stand dive tables is? specifically, I'm interested to know which of the folowing is required for the table to pruduce accurate information

a) each dive must be shalower then the prvios one (during one dive day)

b) no more then two dives can be computed safly. (during one dive day)

c) entering a dive less then (10,30,60) min. after the last dive should be considered as part of the previos dive (or conpleatly avoded)


I have, in the past, been told that each of the above is true, but I no longer trust any of that information. Do any of you know if there are true and for which tables?

(I know that each of the above will increase the chance of DC - I myself rarely use tables and prefer to stick to my vyper.)


onother related questoin is with the "repetative dive grop" or "letters" common on most classical dive tables. Is there someone here that knows how there groups where made, and what they stand for? I have knolage about deco theory - that's again not the question - I'm interested in the relationship between decompression algorithems and table building.

thanks.

Who made these tables, El-ninio?

 

[Dr Deco]

Dear el-ninio:

Tables

I am not aware of any tables that limit you in the three ways that you mentioned. There could be some limitations because of the way the table is setup.

1. To put a table on one or two pages will always require compromises (e.g., you can only track off gassing with one halftime).
2. Ease of use might also dictate that simplifications be made, e.g., in how repetitive dives are calculated.

None of these are related to the algorithm employed in the calculation. The same algorithm could be programmed into a dive computer and it would function without restrictions.

Repetitive Groups

These are always based on the off gassing of a single halftime compartment. Depending on how one sets up the table, that compartment might be the 120 minute one (US Navy) or the 60 minute one (DSAT Recreational Dive Planner).

Again, the arrangement of a table is for simplicity and it provides a “roadmap” of pressure in your body. All cases are not covered to their optimal extent. The algorithm that generated the table (if put into a computer) would generate an optimal profile (within the model limits).

Dr Deco :doctor:

 

[el-ninio]

I had allways assumed that the groups represented some limit on all compartments (no more the x1 on compartment T1, no more then x2 on T2 and so on). your answer serprises me - can you give me some refrence to this?


If table groups are based on single halftime compartment, then repetative deep dives may shift the limiting compartment to a slower one, and therefor increase the chance of DCS with the repeated dives. if a singule halftime load is suffisuiont to track the chance if DCS, what is the point of having 6 or 12 compartments in the model? If you need 12 compartments in the model to represent your state accuratly, how can you represent this 12 dimetion state vector with just one of it's compartments.

how dose this workout?

(I will bring a quotation from the navi manual from wich one can understand that if you do a repetative dive to a depth larger the the previus one, you need to add the bottom times and treat the two dives as if they where a singule dive with the max depth of the two and the total time - but right now I need to rush out - I'm off to dive the Red Sea this weekend, and as much as I like taking about diving, actulay diving wins every time )

 

[Dr Deco]

Hi el-ninio:

Repetitive Groups

For tables, one halftime is chosen and this is always the longest that will be needed for the dive situations. For hardhat divers, it is the 120-minute compartment. When this slowest compartment has dropped to a sufficient degree, then all of the faster compartments will certainly have diminished. For recreational divers with self contained gas apparatus, bottom times of hours is not a possibility, and the off gassing halftime of 60 minutes is found to be sufficient to design a safe table.

These Repetitive Groups determine the amount of off gassing during the surface interval.

Compartment Halftimes

These are different than the repetitive groups and are based on the concept of multiple tissues or mathematical compartments. They range from a short time of five minutes and as long as four hundred minutes. These are used to track the dissolved nitrogen partial pressures in the “pressure map” of your body and determine the on gassing and the maximum time you can remain at pressure before surfacing without decompression is necessary.

It is correct that as the dives, and gas loads, progress throughout the day, the “limiting compartment” will shift to a slower one.

Dr Deco :doctor:

References :book2:

Hamilton, RW, RE Rodgers, MR Powell, and RD Vann. Development And Validation Of No-stop Decompression Procedures For Recreational Diving. Diving Science and Technology. (Pp. 78 + appendix). February 28, (1994)

[This is available from DSAT in California.]

 

[Charlie99]

el-ninio once queried...
If you need 12 compartments in the model to represent your state accuratly, how can you represent this 12 dimetion state vector with just one of it's compartments.

how dose this workout?

When the NDL for a depth is limited by a compartment faster than 60 minutes, the PADI table does not let you get all the way down to pressure group Z.

For example, a 30 minute dive at to the NDL at 80' will only get you to pressure group R on the 60 minute compartment, even though you have hit the max limit on the 20 minute compartment.

Similarly, a dive to 120 is limited by the 10 minute compartment to an NDL time of 13 minutes, even though this only loads the 60 minute compartment to pressure group K.

So, although the faster compartments aren't directly tracked on the table, they do have an effect.

OTOH, repeated lengthy shallow dives may be limited by a compartment with halftime LONGER than the 60 minute controlling compartment of the PADI RDP. Those dives are limited by the special rules for 3 or more dives where any one of them ends in W,Y, Y, or Z pressure groups. The extended surface intervals of the special rules limit the overall average depth such that you will not violate the limits for the very slow compartments.

The choice of 60 minute controlling compartment for PADI RDP(and handling oddball long shallow repetitive dives by exceptions rules) is why the PADI RDP is so much more liberal on repetitive dives than the USN-based tables (NAUI, SSI, etc) that are based on the 120 minute compartment.

 

[BRW]

Yo All,

Picked up the above thread about NAUI Tables.

Info stated there is updated. New NAUI Tables
are based on dual phase (bubbles and dissolved
gas), and are no-fuss, no-muss, no-calc,
no-group compilations across a fuller diving
spectrum than air at sea level, single no-deco,
and 130 fsw max.

New NAUI RGBM Tables (rec and tec) are
NOT based on groups at all, nor dissolved gas.
M-values are replaced by separated phase
volumes in all RGBM Tables. Such is also true
in all RGBM meters (Suunto, Mares, Dacor
Zeagle, Plexus, Hydrospace, Steam Machines),
and commercially marketed software (GAP, ABYSS).

Tissue compartments do couple to bubbles for
gas transfer, and fast ones play on short time
scales (min), while slow ones play on longer
time scales (hrs). Both in rec and tec diving.
But that coupling feeds into bubble growth
in limiting exposures, not just some critical
tissue compartment limiter for dissolved gas.

Is this new -- yes, in our last 5 - 7 yrs
of testing and field validation across the
full spectrum of diving (not just a small
sliver of activity represented by recreational
air and nitrox, basically shallow and no-deco).
But the dynamics are high school physics and
chemistry that even students in 1908 knew
about. But data fitters over almost a century
didn't quite understand how to implement the
full dynamics easily and completely. Some
never understood the dynamics. And their fit
equations were always only 1/2 correct. Better
yet, 1/2 complete.

Plus medical science and physical science have
their own agendas.

Today that is changing for the better in the
estimation of most.

And things are changing fast, even in the mild
world of recreational air and nitrox diving,
especially for reverse profiles, closely spaced
repets, multiday activities, altitude, and high
frequency activities where bubble dynamics come
into full play and CANNOT be properly tracked
with the old stuff (dissolved gas tables,
meters, software based on Haldane's original
data fits via M-values and modern fits using
same approach). ONLY for single dives within
NDLs do modern phase models and Haldane
models overlap. After that, things change,
despite what you might be reading in Training
Agency blatter about bub models. A recent PADI
article comes to mind as SHORT on fact about
RGBM, and overlap with recreational (and tec)
diving. In fact, it's mostly WRONG about all
bubble models and data fits to such. And
validation and use.

Oh well, Rome wasn't built in a day either.

Cheers,

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr

 

[BRW]

JC,

Change does take time, sure. Rome wasn't built in
a day, as I said. But a century to discard dissolved
gas "data fitting" with inefficient diver staging is too, too
long. It's criminal. Even Haldane might agree.

Especially when it's not rocket science.

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr
;-0