When is it okay to exceeding training limits?

[stuartv]

And here I was thinking that 130' was tied somehow to the physics of O2. I do like to make stuff up...

I was thinking that it was somehow related to the MOD of EAN32 being 40m (for 1.6ATA ppO2).

Now, don't ask me why I would think that instead of, say, using the MOD of EAN30 or even EAN28 or less. Or, really, why anyone would use any of those over the MOD of air, if that's what they were using to decide the safe limit for Rec diving....

Now that I think about it more, I suppose it's more likely that EAN32 has become the most common blend of Nitrox because it's the richest blend you can use at any Rec depth. So, max depth implied Nitrox blend, rather than the reverse.

And, looking at the NOAA NDL table for air, I see that you only get 10 minutes at 130'. Maybe somebody decided there was not much point in diving deeper than that, since you wouldn't even be able to stay 10 minutes, so they made that the limit. Which I guess is just another way of saying what boulderjohn said. Past 130 (on air), you're pretty quickly into mandatory deco dives, right?

 

[Basking Ridge Diver]

DSAT and PZ+ take you down to 190 feet on air - 5 mins on DSAT and 4 mins on PZ+ - no deco all in NDLs. To your point it is very much like a bounce dive.

 

[RJP]

BTW - my son and I both dive with Ponies now

Cool!

 

[boulderjohn]

DSAT and PZ+ take you down to 190 feet on air - 5 mins on DSAT and 4 mins on PZ+ - no deco all in NDLs. To your point it is very much like a bounce dive.

Remember that bottom time includes descent time. If you use a common 60FPM descent rate, it will take more than 3 minutes to get to that depth. That leaves you less than one minute of true bottom time.

 

[Lorenzoid]

Did you take that photo at Steel Pier? I see you're from Jersey.

Cool!

 

[Basking Ridge Diver]

Remember that bottom time includes descent time.

I used to believe that - so feel free to correct me. But I have shot down to 80 feet - I can clear very quickly and have no problem dropping much quicker than 60 fpm - looking at my pdc and downloading after - it does not appear to be so... I get the full bottom time per DSAT - descent time doe not appear to impact my dive time... Am I imagining that?

 

[Akimbo]

And here I was thinking that 130' was tied somehow to the physics of O2. I do like to make stuff up...

I was thinking that it was somehow related to the MOD of EAN32 being 40m (for 1.6ATA ppO2)....

Nitrox didn’t exist in recreational diving when the training industry adopted the 130' recommendation. Dive computers also were not a consideration… since they virtually didn’t exist yet. Same story with Oxygen Toxicity. The US Navy’s maximum recommended PPO2 was 2.0, not 1.4ish. The part that has not changed is the amount of gas the “typical” diver carries and consumption rates. As I recall, Nitrogen Narcosis wasn’t the major driver since the great majority of divers don’t start doing stupid things until 150-165' plus.

 

[boulderjohn]

I used to believe that - so feel free to correct me. But I have shot down to 80 feet - I can clear very quickly and have no problem dropping much quicker than 60 fpm - looking at my pdc and downloading after - it does not appear to be so... I get the full bottom time per DSAT - descent time doe not appear to impact my dive time... Am I imagining that?

Bottom time is defined as the time you begin the descent to the time your begin your ascent to the surface. Your descent really doesn't make a dimes worth of difference on a typical shallow NDL dive, but it starts to matter as you get deeper.

To see what I mean, run dive profiles in a program like V-Planner. It will automatically assume you are descending at 60 FPM. On a 190 foot dive, it assumes you took 3 minutes to get there. That means that for the first 3 minutes of the dive, it makes its calculations of your gas loading on the assumption that your average depth was 95 feet. If you descend at greater than 100 feet per minute, which can be done, your average depth for the first 3 minutes will be closer to 150 feet.

Now plug that idea into your 4 minute NDL at 190 feet. If you descend at that faster rate, your average depth for the dive will be about 40 feet deeper than the program anticipates.

BTW, for that 4 minute air dive to 190 feet, V-Planner does want you doing a decompression stop.

 

[Basking Ridge Diver]

BTW, for that 4 minute air dive to 190 feet, V-Planner does want you doing a decompression stop.

Done and done - you are correct - so the question is how closely does V-Planner match DSAT or PZ+ - is it close? Deep stops seem to bring the deco obligation down but do not eliminate the obligation.

 

[boulderjohn]

Done and done - you are correct - so the question is how closely does V-Planner match DSAT or PZ+ - is it close? Deep stops seem to bring the deco obligation down but do not eliminate the obligation.

I don't know. My main point was that as you increase the depth and decrease the total bottom time, the descent rate becomes increasingly important in relation to total bottom time.

Here is a 10 year old study you might find interesting. It is a comparison of the algorithms used in dive computers of that day. It is interesting because it shows how very different the algorithms we use are, and it therefore shows how far off we are from having this whole thing nailed down.