Thoughts on a new computer function

[boulderjohn]

You begin your ascent, and you reach your first gas switch. You make the switch and make the change on your computer. You computer changes its decompression calculations using the new mix. This process continues through any future changes until you reach the surface. Once on the surface, the computer continues to track your tissue off-gassing and will be able to apply those calculations to a future dive. To do this, it changes to the gas it assumes you are breathing on the surface--air.

On many computers, you can check at any time after a dive to see how your tissues are doing. Some will have a graph showing how close your tissues are to m-values at the moment you check it after a dive. YOu can see how your tissues are off-gassing as you breathe the surface air.

But what if you are not breathing air?

Many technical divers will breathe a decompression gas, including pure oxygen, on the surface for a period of time after a dive. Even at the recreational level, I remember seeing some texts showing divers sitting on a boat breathing nitrox between dives. The texts said that this gave them a cushion for the next dive, a cushion they could not measure in any way. It would seem to me that it would take only a minor programming change to allow a computer to use a gas other than air while in the surface mode.

For me personally, the benefit would be for an ascent to altitude following a dive. NOAA and the US Navy have ascent to altitude tables showing when it would be safe to ascend a certain amount following dives. If you are in a certain pressure group on their tables following a dive, you could ascend so many thousand feet after so many hours of surface interval. NOAA also had a table showing how many pressure groups you would move if you were breathing oxygen rather than air during that time, which would allow you to make that ascent sooner. The basic idea has already been done.

I suspect that computer manufacturers would be hesitant to include any technology that could imply that they are telling you it is OK to do something that has not been studied scientifically. But I don't need anything more than already exists in that regard. Before I ascend to altitude, I can look at my Shearwater computer after a surface interval and make a personal judgment about my tissue loading. The only difference would be that if I am breathing oxygen for some of that time, I would see the kind of difference that makes.

 

[tbone1004]

@boulderjohn I've wondered the same thing actually and curious how many requests @Shearwater has seen for it. "Surface deco" after technical dives where you are breathing O2 while sitting at the surface before getting up the ladder or hauling out on shore is a pretty common occurrence but obviously just used as an "Extra buffer" for us before hauling out since we can't track it once the computer "ends the dive". I suspect it isn't an available feature as a CYOA to make sure that you don't continue to decompress on whatever your higher ppO2 gas is *we are all guilty of getting back in the water without changing our gas back from O2 at some point or another*

You'd have to check this, but if you set the surface interval long enough for the "end dive" on the shearwater, if you stay on O2 at the surface for 10-15 minutes it may start counting down. You'll have to check with probably @tcoen to see what it does. I imagine if it was enough of a push they could set a "surface deco" mode but again, unsure what the legal risk of that would be for divers turning it on to clear their tissues before the next dive.

 

[kelemvor]

It's a good idea. It would take less effort to implement than other user requests that shearwater has already implemented since there would be no hardware changes required. Specifically I'm thinking of AI and Audible alarms.

It's just a matter of whether they think it would be a selling point, I suppose. Surely there's some small development expense and probably a larger testing/debugging expense involved.

If you really wanted this in "any" computer, you could probably write the code for the OSTC computers yourself.

 

[rhwestfall]

Interesting, but the problem I see is that it is too easy to also nose breathe thus not truly doing what the modeling says.....

 

[Diver0001]

I see too much risk of the user forgetting to put the computer back in air mode once they stop breathing the other gas.

 

[boulderjohn]

Interesting, but the problem I see is that it is too easy to also nose breathe thus not truly doing what the modeling says.....

That is something well within the control of the individual.

 

[rjack321]

That is something well within the control of the individual.

Very fallible individuals as well.

 

[rhwestfall]

remember John, we now have to "bubble wrap" everything...... Stupid monetary rewards for idiocy seems to be too much the mainstream....

Torte Reform.......

 

[rjack321]

remember John, we now have to "bubble wrap" everything...... Stupid monetary rewards for idiocy seems to be too much the mainstream....

Torte Reform.......

More like cultural shift, countries other than the USA don't have this annoying habit of chasing ambulances.

 

[J-Vo]

The key to not having to "bubble wrap" is giving full control to the end user. So far Shearwater has done a pretty good job of this. Maybe a large flashing warning display when you are not set to 21% at the surface.

I would find this functionality very useful as my situation is the same as @boulderjohn .

I would also like to see similar functionality in planning software for both pre/post dive altitude/gas changes. The ability to plan for my drive to altitude before diving as well as after the dive would much better than "winging it" like I have to do now.