Shallow Diving and flying

[Dr Deco]

Hello Readers:

An Exact Science - - -

It always "raises my hackles" when someone says that decompression is not an exact science. A better phrasing of this would be the following. “Under laboratory conditions, DCS is fairly predictable with a given test population. However, with a diverse population under wildly varying conditions, the ‘dose’ of nitrogen is variable even when the bottom time and depth are determined.

In addition, such factors as tissue micronuclei and tissue perfusion must be assumed equal for all when it is known that it is not.”

Gas Loads and Halftimes

When I first noted the posting above from gcbryan, I thought, “Wow, it can’t be that simple, can it?” No, it is not.

Putting the time/depth numbers in, and calculating the nitrogen loads, one can determine that “30 minutes down has a 180 (= 30 x 6) washout duration” holds only for a few cases - and then only for short half-time compartments [5 to 10 minutes].

Swimming Pool and Then Flying

This is an extreme example, and it fundamentally involves a trivial nitrogen uptake. While some [statistical] models will indicate a finite probability for any decompression, no one has ever had the “bends” following an elevator ride. You also need nuclei, but no one acquire the “bends” at the gym. [It might be possibly benign overuse myalgia, but not DCS.]

Too little is sometimes too little.

Dr Deco :doctor:

 

[gcbryan]

Hello Readers:


Gas Loads and Halftimes

When I first noted the posting above from gcbryan, I thought, “Wow, it can’t be tha simple, can it?” No, it is not.

Putting the time/depth numbers in, and calculating the nitrogen loads, one can determine that “30 minutes down has a 180 (= 30 x 6) washout duration” holds only for a few cases - and then only for short half-time compartments [5 to 10 minutes].

Dr Deco :doctor:

Can you explain (in simple terms) why this only holds for a few cases and then only for short half-time compartments? This is in the context of recreational diving of course where most dives will be an hour or less.

Thanks.

 

[gary-ramey]

It always "raises my hackles" when someone says that decompression is not an exact science. A better phrasing of this would be the following. “Under laboratory conditions, DCS is fairly predictable with a given test population. However, with a diverse population under wildly varying conditions, the ‘dose’ of nitrogen is variable even when the bottom time and depth are determined.

Sorry to raise your hackles but I'm relatively new to the sport and what I read on this thread is against the things I've been "taught". So, as with any student who wishes to continue learning, I'll ask questions which will often raise some hackles. Given you stated "with a diverse population under wildly varying conditions, the ‘dose’ of nitrogen is variable" aren't you splitting hairs? To an engineer uncontrolled variables literally translate to "not exact".

 

[spectrum]

PinkPADIgal,

Are we safe in assuming that this 4 dive day is the only diving of the trip?

We aren't talking about the last day of a dive intensive week are we?

Pete

 

[limeyx]

I have to do checkout dives for open water students. If I do 2 dives in less than 20 feet of water for about 15 minutes each, (1 hour surface interval between) what kind of risk do I take flying 6 hours later? Would hitting up my O2 bottle help me?

Thanks for the input.

I cannot give you any advice, except that IMO flying after diving and (by extension) DCS is inherently not well understood. People have been bent on very shallow dives that should be fine and not bent on dives that they "should" have been bent on.

There was a recent report of a guy in England, doing 2 conservative rec profiles on 32% on the same profiles as his buddy on air. The 32% guy took a bad hit and into the chamber, and the air guy was fine. Maybe a PFO, maybe dehydration but maybe not -- who knows ?

I did 10 days of 3-4 dives per day in Nov last year (admittedly average depth 40-60 feet and on nitrox) and then flew the next day with no ill effects.

I just got back from a two day trip. Day 1 was a dive to 140 (approx 110 feet average for 30 mins) followed by a dive of approx 50-60 feet average for 45 mins

day 2, was a 150 dive (130 average for 30 mins, 156 max depth) followed by 60 mins at 50 feet average (on 32%) and then flying about 4 hours later with no ill effects.

I did similar trips last year.

Am I "pushing it?" honestly, I have no way of telling, and I cannot advise anyone else to do the same thing.

I think my deco ascents are clean enough that flying 4-5 hours after diving does not significanly increase my chances of DCS.

However, I also have to accept the fact that diving frequently, it's almost a given that I am going to get some kind of "undeserved hit" at some point due to the lack of complete understanding of how this stuff works.

Getting in the water is a risk and so is to some extent flying afterward.
The recommendations are there, but as Lamont pointed out -- they may be not based on many or any real-life scenarios.