different air tables

[Remy B.]

How many versions of US Navy tables are in use currently by the dive agencies out there or is there a level of conservation added depending of the agency ?

I have 3 different tables, a PDIC, an old one given to me by a PADI dive center ( but no identification of the agency it only say 1984 US Navy Standard Air Deco Table ) and my latest one from TDI when I did my nitrox course with them, the PDIC and old PADI are similarly close but not equal and uses the 10ft as the shallower depth for Deco, the TDI uses 20ft as the shallower depth for Deco but with a lot of more time = more conservative

Can one expect different tables lets say from NAUI, SSI, or IANTD

 

[Bob DBF]

You can expect different, but close, tables from different sources and depending on the date it was made. Pick your poison, and read all the notes. When I started diving there were just the Navy tables.

I believe the reason for the length of time at a 20' stop rather than a 10' stop is because you off gas slower, rather than being more conservative. You changed two variables, time and depth, rather than one.


Bob

 

[Belzelbub]

Can one expect different tables lets say from NAUI, SSI, or IANTD

Yes, but they'll be pretty close. Here's a chart I stumbled on a while back. Just shows the NDL times at certain depths for a few different agencies and some DC algorithms.

 

[TSandM]

There are a number of underlying assumptions made when tables are generated. The number of tissue compartments that are considered, the half-lives that are assigned to them, which compartment is used for calculating repetitive dives, the M-values which are used, and the degree to which the formation and expansion of bubbles is considered, will all change the output. In addition, some models use parallel compartment loading, and others use serial.

The outputs are most similar for the first dive, and tend to diverge more for repetitive diving.

Lippmann & Miller's Deeper into Diving goes into this quite well.

 

[SanDiegoSidemount]

Isn't this an old diver joke? Ask 10 divers what the NDL is for air at 60' and you'll get 15 answers. Ask a tech diver, and they'll need to boot their laptop to tell you what V-Planner says.

This just demonstrates how sketchy the so-called "science" of decompression really is. Just staying within any of any of these NDLs is no guarantee you won't get bent. There are lots of competing models and algorithms, but what any of them spits out is really just an "educated guesstimate".

If you dive hung-over, jet lagged, or dehydrated, any of these alone could end up being a bigger factor for DCS than any of the differences between tables and/or computer models.

 

[NAM001]

I found long ago that you have to read the notes. the difference I saw was how bottom time was calculated.
water entry to start of assent
bottom to end of assent
start of decent to end of ascent.

decents are usually faster than ascents

I thought that most had gone to,,,, at depth or start of decent,,, to start of ascent.

There is only a minute or 2 difference perhaps.

 

[jboneng]

There are two main groups of diving tables, perfusion based tables (using haldane/workman/buhlmann theory), like the US Navy tables, and diffusion based tables (using VPM, RGBM, TBDM models), like the PADI RDP table.
The main differense behind them is that perfusion based tables tries to avoid bubbles in your tissues, while the diffusion based tables acknowledge that you have bubbles in your tissues but tries to avoid those bubbles growing to critical mass.

The perfusion based tables have some variations since ther are different algorithms with different number of tissue-compartments with different halftimes, MZero Values and M Value slopes.
Also after PADI did its original research with doppler ultrasound, the US Navy changed the controlling tissue-compartment from the slowest one to one of the more quicker compartment, some of the organizations that have tables that is based on the pre-changed US Navy tables did not update their tables, like SSI and Norwegian Standard Table.

 

[tursiops]

There are two main groups of diving tables perfusion based tables (using hadaine/buhlmann theory), like the US Navy tables, and diffusion based tables (using VPM, RGBM, TBDM models), like the PADI RDP table.

PADI/DSAT RDP is diffusion based? That's not the way I read it......

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[Bob DBF]

I found long ago that you have to read the notes. the difference I saw was how bottom time was calculated.
water entry to start of assent
bottom to end of assent
start of decent to end of ascent.

decents are usually faster than ascents

I thought that most had gone to,,,, at depth or start of decent,,, to start of ascent.

There is only a minute or 2 difference perhaps.

Make that from start of decent to start of direct ascent to the surface and a rate of ascent will be specified. This makes a difference in that a even a deep stop turns the dive into a multilevel dive, unless it's use is specified in the ascent instructions by the table, so being "safe" could get you bent.



Bob
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I think that advocating unsafe and dangerous practices is both stupid and foolish. That is why I don't tell people to do what I do. Dsix36

 

[Remy B.]

I'm talking about US Navy Tables, all three tables are identified as such.

here are some differences between the three, the most conservative and almost impossible to make bubbles will be the table handed out from TDI

PDIC USN Air Table ( given to me by the IDC ) it only go to 140ft and 25min max bottom time

Depth / Bottom Time / Time to 1st Stop / DECO stops / Total Ascent time
70ft 20ft / 10ft

90min / 2 min / - / 23min / 25:20min

140ft / 25min / 4 min / 2 min / 14min / 20:40min


1984 USN Standard Air Deco tables ( given to me by a PADI IDC ) it was very old material he had so he give it for free, the new ones I needed to pay from them ( even that I had my wife get certified with them, they wanted me to pay even for her tables, example of Put Another Dollar In )

Depth / Bottom time / Time to 1st stop / DECO stops / Total Ascent Time
70ft / / 40ft / 30ft / 20ft / 10ft
90min / 1 min / - / - / - / 23min 24:10min

140ft / 25min / 2 min / - / - / 2 min / 14min 18:20min


190ft / 30min / 2:30min /1 min / 8 min / 19min / 32min 63:10min



TDI USN Air DECO Tables ( given to me by the IDC )

Depth / Bottom time / Time to 1st stop / DECO stops / Total Ascent Time
70ft / 60ft / 50ft / 40ft / 30ft / 20ft
90min / 1:40min - / - / - / - / 64min 66:20min

140ft / 25min / 4 min - / - / - / - / 26min 30:40min


190ft / 30min / 4:40min - / 6min / 8min / 14min / 111min 144:20min


There is a lot of difference between the TDI table and the other two tables, is TDI counting in work load, and there for make it more conservationist table ???
I don't see how you can get bend with this table which is good but the amount of gas you need to carry is double, that can be the negative side of this table if you want to carry just air for Deco of course.

then it come in that all three agencies advocate to use computers which IMO is good, now which Algorithm to follow of those different brands of DC ???, here I agree this is not an exact science.

---------- Post added April 15th, 2015 at 11:34 AM ----------



PS: I tried to arrange the numbers but the web site format will not allow spaces or I don't know how to do it. ( I tried Font type coded to see the differences in depth /DECO stops and Total Time but it still a mess )