In dive, manage having EAN programed into computer while diving air?

[tbone1004]

Place of dive tables in modern diving

I'll yield to that one!

 

[BRT]

Problem is that if you notice your computer is set wrong when you are 50 minutes into a max 100 foot dive none of the tables or rules of 120 or 130 will get you out.

 

[saridnour]

Interesting that there is no "official" recovery. In hindsight you'd think that a computer should be able to recalc in an emergency or run a dive plan with the data. Shearwater allows a dive plan to be done at depth so wouldn't think to be to hard make available. Could be a safety or cost vs use thing.

@BRT and was what I was trying to figure out.. what is a true recovery plan.

@tbone1004, Interesting thoughts on the "rule of xxx" it would give a little confidence in a guesstimate but still seems a bit loose with numbers to base a plan from (but a good guideline if unfamiliar). I will need to keep this in mind with a rule of 90 based on my conservatism. I use 35/70 and if I went back to a 20/90 and recalc that dive I do not have any deco obligation so was already under that safety net and why I do it.
Your idea of pushing down the GF high though is interesting. Since I already run a conservative GF I'd really haver to knock it down if was to happen again to stay that conservative, but then again that conservatisum is there to incase something like that happens to a degree. The thought of running a dive plan and adjusting the GF could give some indicators while in a dive of what offset may be needed. I will have to play with that on my next deco stop with my backup computer.


Anyone have any other ideas?

-Andy

 

[Esprise Me]

Thanks for starting this thread; I love thinking through these what-ifs! I had an idea and would love feedback. I ran the numbers on PADI's tables for air and Nitrox 32, and found that, between 70 and 120 feet, the Nitrox table allowed approximately 50% more bottom time than the air table. So if you've been doing a long, multilevel dive with a max depth that would put you in deco if you calculated a square profile, but your computer says you have 15 minutes of NDL remaining, and only then do you realize it's still set to 32% instead of air, you could ballpark that you've really got about 10 minutes of NDL remaining. Starting your ascent immediately rather than waiting 10 minutes seems prudent, but at least you're not freaking out about deco stops you probably don't really have to do. Thoughts? Obviously this only works with you having already calculated the average NDL increase for the gas your'e NOT using; if this conversation comes back to you someday when you're diving air that your computer thinks is 36%, this won't help.

 

[NAM001]

Interesting that there is no "official" recovery. In hindsight you'd think that a computer should be able to recalc in an emergency or run a dive plan with the data. Shearwater allows a dive plan to be done at depth so wouldn't think to be to hard make available. Could be a safety or cost vs use thing.

@BRT and was what I was trying to figure out.. what is a true recovery plan.

@tbone1004, Interesting thoughts on the "rule of xxx" it would give a little confidence in a guesstimate but still seems a bit loose with numbers to base a plan from (but a good guideline if unfamiliar). I will need to keep this in mind with a rule of 90 based on my conservatism. I use 35/70 and if I went back to a 20/90 and recalc that dive I do not have any deco obligation so was already under that safety net and why I do it.
Your idea of pushing down the GF high though is interesting. Since I already run a conservative GF I'd really haver to knock it down if was to happen again to stay that conservative, but then again that conservatisum is there to incase something like that happens to a degree. The thought of running a dive plan and adjusting the GF could give some indicators while in a dive of what offset may be needed. I will have to play with that on my next deco stop with my backup computer.


Anyone have any other ideas?

-Andy

I thought about that also ,,, and then I had to ask how does it know whether you are correcting an error in original set up or just a gas change. Any gas change is started from the time of change. IO think one would have to be pretty able when it comes to reconciling a situation like this. Speaking shearwater I think I would look at the average depth calculated use the 120/130 rule and determine from that how far past NDL i really was. and then do some fudging for level of conservatism to see if I could reason some extension of NDL from say medium to low conservatism. I could find that I am only a few minutes over the limit and perhaps toss a coin from there. We also have the ability with shearwater to change to a custom GF and shift to 100 100 to also see what times it gave me. Then stay at min depth allowed per GF to speed the off gassing. I suppose one could also do a equivilant air depth calc if able to do so and then fudge the avg. depth from nitrox avg depth to air. No matter what it is not a beginner diver problem. I dont remember,,, is there a setting on the shearwater to retain the last gas used for repeditive dives if surfaced over 10-15 minutes. Ive used so many computers over the years I dont remember.

 

[NAM001]

I just went to look at some ead tables air is 21 teh OP used 30 thats about a 10% increase in O2 and the same decrease in N2 that 10% reduced depth of 100 to 90 ft. so if the puter said avg depth on 30% was 60 ft then I guess one could say that the air equivilant depth would be low 50'S and apply the 120 rule to that. That might cancel out 10 minutes of the overstay. I might have that backwards. air depth is always shallower than nitrox depth

 

[tursiops]

I think I would look at the average depth calculated use the 120/130 rule and determine from that how far past NDL i really was.

Not average depth......you need to use maximum depth. Tables, and the "rule," use maximum depth.

 

[tbone1004]

@saridnour I would definitely not want a computer to be able to completely revert an entire dive underwater, that's scary. Going from EAN30 to air is one thing, but going from air to say EAN40 is a very different discussion.
If you are already diving conservative GF's, then pushing it down that much more doesn't change the actual dives conservatism. It replicates your current dive profile on the gas that you were supposed to be on. Now in the opposite direction, like you said, the GFhi would have actually been 90, and if that's within your tolerance for decompression, then that's perfectly fine.

@KWS Shearwater only allows you to change the GF-hi mid dive, though you can always see the GF99 value and ride that.
Shearwaters also hold the last gas used and do not revert to previously used gases. I get caught during predive checks with mine on 99% far too often, but that one at least flashes at you once you hit 20ft.

 

[HKGuns]

I wonder how hard it would be to have an air integrated computer detect the gas being used?

Doing so might require some additional maintenance of the transmitter, but keeping it only accurate enough for an idiot check may be of some value, increase safety and be of minimal hassle.

I don’t know enough about them to know if there is room to add this functionality.

A flashing screen that tells you this gas doesn’t seem to match your settings would be a good reminder in this case.

 

[tbone1004]

@HKGuns functionally impossible. We have enough issues measuring ppO2 at ambient pressures, to try to measure it at 300bar/4500psi is not possible with todays technology, nor do I see it being useful for any non diving application