Decompression Tables for Nitrox

[Basking Ridge Diver]

All good fun, but don't dive an Excel table you made yourself, obviously.

I learn by hands on - the hardest part was converting the Naui and Navy tables into records that I could read with excel formulas.
The Naui table is 158,852 rows and the Navy table is 169,359 rows because I had to include all the SIT permutations of the letters...

I have used it to validate my plans for diving (double checking the tables for accuracy) - I do wear a PDC - but the exercise of doing it reenforced my understanding of the tables.
It is pure exercise in playing with SIT and Bottom Time to see the impacts on NDLs as well as incurring some Deco penalties.

 

[Aquabot]

Originally it was taught to ascend no faster than 60 fpm. Some may still teach that but generally it isnt.

To answer your question, yes your ascent rate matters. Decompression tho is still a theory tested on every dive and nothing can guarantee that you will not develop enough "bubbles" to become bent. People do get DCS even while following NDL.

A slow ascent is prudent because it allows you to control your ascent so that you do not "miss" or blow past stop. Which depending on your depth and time at depth could prove fatal.

May I ask, why such a interest in decompression if you are aware that you don't posses the skill level to safely conduct those type of dives?

Sure - I am playing with Excel just because I am not diving now. So I built an excel worksheet using Naui Tables and Navy Tables that allows me to enter 3 dives (Depth in 10 foot increments (40 to 130 ft for Naui and 190 ft for Navy), Time (Minutes only) and on the 2nd and 3rd Dives SIT (Minutes)). It kept me busy - it does both NDL (In Green with Ending Letters for each dive) and Decompression times (in Red with Ending Letters and Deco Time). Any way it started out as a challenge to see if I could do it - it works and now I am thinking of enhancing it.

I am OW and Solo Certified - I may get AOW this spring because my son is now diving with me. But I was never interested in Nitrox or Deco diving - now it is just a mental exercise and the more I learn the more I realize how complex this can be to plan. I don't see myself going beyond this point but it is fun to explore and think about the options as well as reading the threads in various forums it allows me to understand the concepts and points being made.

So I appreciate the small amounts of knowledge being shared - but at this point I don't have the wallet or the dedication to pursue it beyond the theoretical point.

That's awesome. Some of my most favorite dives have been with my dad .
Just stay safe so we can continue to have these kinds of discussions lol

 

[Basking Ridge Diver]

I have been playing with the HLPlanner - I have a fundamental question.
Same Depth and time - 120 feet for 20 mins - vary the Deco Last Stop from 20 feet, 15 feet and 10 feet and you get various Deco Times.
10 Foot Deco Last Stop seems to give you reduced time results - every time.

So my question is two fold -
Is this a bias on this particular software on a 10 foot last stop?
Should I change my recreational safety stops to 10 feet? Currently I use 20 feet based on previous articles that I have read...
Thanks

 

[HIGHwing]

The problem with Excel tables is that you're learning equations, but perhaps not the theory and basis. Let's try a really simple question:

Diver A and Diver B go on a dive together as buddies. They decide to make a 120ft air dive to the limits of the NDL on their computers, and they opt to insert a 5 minute saftey stop before returning to the boat. Both divers enter the water, leaving the 120ft depth when their computers say they have 5 minutes of NDL remaining. Arriving at the 20ft safety stop Diver A recognizes that he's short on air and elects to return to the boat leaving Diver B at 20ft.

Which diver is offgassing more quickly, why?

 

[Basking Ridge Diver]

The Diver on the surface is off gassing more quickly - due to the pressure or lack thereof.
But I would be concerned that they are releasing pressure too quickly and may regret running out of air...

Is there an optimal depth to off gas on your last stop? Or is it based on personal choice?

 

[victorzamora]

Is there an optimal depth to off gas on your last stop? Or is it based on personal choice?

This is the kind of question HIGHwing could've asked as well. So, ask yourself that question right now before reading on.

It's both. The optimal depth to offgas on your last stop is the one where you can do so safely while mitigating DCS risks. The level of safety you impart changes this. Conditions at the surface change this. Your breathing gas changes this depth. Plenty of factors (personal or otherwise) change the actual depth....but the theory is that you want to be as shallow as possible with minimal DCS risk and tissue damage. 20ft on O2 is my preferred last stop depth, but some caves and ocean conditions are friendlier to 15ft or 25ft.....so it depends.

 

[HIGHwing]

This is the kind of question HIGHwing could've asked as well.

Indeed, I could have, but I like my question much better.

 

[Basking Ridge Diver]

So - based on my experience of hanging on an anchor line or just off to the side with a Jon Line - 20 feet seems to be better for me. Otherwise the higher I go the more apt I am to bouncing through my stop / ceiling...
Hey wait - did I answer my own question?
You guys rock!

********
Last question - do you need to be breathing to off gas? Skip breathing or any other method - does it delay off gassing? Or is it off gassing through cells and blood that matter?
Yes - I agree / understand no one should be holding their breath or skip breathing... but it still begs the question for me.

 

[whitefang21]

You can also plan if the waves are really rocking hanging on at the stop can be dangerous. Your last stop should be ideal to the greatest change in decompression and optimal for your breathing gas. Pure o2 PPo2 @ 1.6 is 20 feet.

So - based on my experience of hanging on an anchor line or just off to the side with a Jon Line - 20 feet seems to be better for me. Otherwise the higher I go the more apt I am to bouncing through my stop / ceiling...
Hey wait - did I answer my own question?
You guys rock!

 

[victorzamora]

Indeed, I could have, but I like my question much better.

I thought your question was SUPER clever, and only mostly covered in BRD's answer. My point was that BRD asking his follow-up question is another example of someone "learning equations, but perhaps not the theory and basis"