Further decompression to lessen no fly time?

[Ghost Diver #]

In theory, could you decrease your no fly time by continuing to decompress/off gas on the surface? I.e continuing to breath a hyperoxic gas.... Not going to try it I was just curious .

 

[RainPilot]

Yes, any enriched gas on the surface would reduce your no fly time.

We used to prebreathe pure O2 before high altitude unpressurised operations (like HALO etc)

The Cochran dive computer made mainly for the military actually has a surface gas option for this purpose.

 

[Ghost Diver #]

Oh, well that’s cool thanks. Kinda figured it would work but I didn’t know it was done in practice.
Thanks

 

[JohnnyC]

It's all about pressure gradients. In theory, you could desaturate your tissues enough that you're on-gassing while you're walking around going about your day.

Interestingly enough, one of the potential benefits to using a rebreather (or a lot of high PO2 OC gas) is that, provided done correctly, you could get out of the water and hop straight on an unpressurized aircraft without any issue whatsoever. Practically speaking, it's out of the realm of being useful, but the theory is sound. Nobody does it, but you COULD.

 

[boulderjohn]

It's all about pressure gradients. In theory, you could desaturate your tissues enough that you're on-gassing while you're walking around going about your day.

Technical divers who finish their dives decompressing on oxygen will usually be on-gassing in their fastest tissues during a surface interval.

The NOAA ascent to altitude tables used to tell how long you had to wait to ascend to different altitudes, depending upon what pressure group you were in. They also had a table telling you how you would move through those pressure groups more quickly if you breathed oxygen during your surface interval. (I can't find them any more.)

When I do a decompression dive and then drive home later in the day, I breathe oxygen during the first part of the drive. Just before I have driven an hour, I will ascend to aout 2,500 feet above my dive elevation. I will then hold nearly that same elevation for another hour and a half before ascending another 800 feet. I will usually breathe pure oxygen for most of that distance.

There is, unfortunately, no good data on this, so I am not officially recommending any course of action--just telling you what I do, right or wrong. If Shearwater would simply allow divers to identify a specific gas for breathing during a surface interval the way they do during the dive, that would make options pretty clear.

 

[KevinNM]

It's all about pressure gradients. In theory, you could desaturate your tissues enough that you're on-gassing while you're walking around going about your day.

Interestingly enough, one of the potential benefits to using a rebreather (or a lot of high PO2 OC gas) is that, provided done correctly, you could get out of the water and hop straight on an unpressurized aircraft without any issue whatsoever. Practically speaking, it's out of the realm of being useful, but the theory is sound. Nobody does it, but you COULD.

There was a guy developing deco algorithms at Los Alamos that I heard were intended for that purpose. Though it involved them loading a large heavy object on the plane too.

 

[Johnoly]

...one of the potential benefits to using a rebreather ...

.. I will usually breathe pure oxygen for most of that distance..

There was a guy developing deco algorithms at Los Alamos....

Yes, .

Just wanted say THANKS for a very unique topic that is rarely discussed on SB...Always learning here !!

 

[JohnnyC]

I definitely want to reiterate that nobody in the recreational or technical realm is doing SurD in order to decrease their no fly time with any sort of certainty.

Like John mentioned, there are people who breathe supplemental oxygen on the drive home due to altitude concerns, and like Kevin said, there has been some limited research into it, and while the theory is sound, there's really no definitive guidelines as far as procedure or standards, so be VERY careful trying to sort this out yourself. The best course of action is still to follow your certifying agency guidelines for flying after diving. Like John mentioned the NOAA has some info about it, but I haven't seen it nor have I practiced it, so I would be hesitant to recommend it with any sort of expert opinion.

I'm sure there's a NEDU study buried somewhere in some folder bordered with red tape that's designed for sneaky squirrels coming over the beach with their LAR-V's and hopping in the back of a C-130 with a high value target after a platoon of Rangers has blitzed an enemy airfield, but I highly doubt that any of that would apply to my fat a$$ piddling along a reef and then jumping on a Delta flight after a margarita and an awkward TSA pat down....

 

[RainPilot]

O2 rebreathers mean never having to say “No Fly”.

 

[boulderjohn]

Like John mentioned, there are people who breathe supplemental oxygen on the drive home due to altitude concerns, and like Kevin said, there has been some limited research into it, and while the theory is sound, there's really no definitive guidelines as far as procedure or standards, so be VERY careful trying to sort this out yourself.

That ^^^ is an excellent caution.

As someone who drives to altitude after diving many times a year, this is an important topic for me. I have done enough research to know there is almost no research on it. I recently asked some very prominent and highly knowledgeable experts on decompression theory to help me write an article on ascending to altitude after diving. They politely refused. They did not want to be quoted as even appearing to advocate something that has not had enough testing to justify a recommendation.

But people have to do it. With or without an expert opinion, people have to decide what to do. So I took a deep breath and wrote an article on ascending to altitude after diving. It is located on my resources page, along with several other useful items, including the NOAA ascent to altitude table and the US Navy ascent to altitude table. You will see that I wrote as clearly as possible in two different places that nothing in that article should be construed as a recommendation from me. It is just a compilation of facts that will help you make up your own mind.

I was recently in a situation in my usual diving environment in which a fellow diver had some mild symptoms on a morning dive. They went away. We were scheduled to dive the next day. We cancelled that, and instead of driving home over the pass, we spent the night in a local motel. Was that necessary? Beats me, but if I'm going to make a mistake, that's the direction I want to make it.