Doolette's Alert Diver Interview

[KevinNM]

The old GUE ascent profile had stops starting at 75% of maximum depth, or so I have been told - that was all before my time.

 

[boulderjohn]

The old GUE ascent profile had stops starting at 75% of maximum depth, or so I have been told - that was all before my time.

They don't do that now?

I was trained by UTD to do the first stops at 75% of maximum depth (or average depth if not a completely square profile), and I don't believe they have changed--that could be wrong, though.

I just ran a profile through 3 configurations in multi-deco and...

First stop for VPM-B/E (+3) = 65% maximum
First stop for Buhlmann ZHL-16-C (GF 20/85) = 60% maximum
First stop for Buhlmann ZHL-16-C (GF 50/80) = 45% maximum

 

[KevinNM]

They don't do that now?

It's more complex, but for Rec dives it's 9m/min to 50%, then 3m/min, for tech dives at 75% is where you adjust your ascent rate from 9m/min to 6m/min (and then there are lots of other elements that determine when and what you do next).

 

[Ayisha]

They don't do that now?

No, 50% of max depth or 65% of max ATA for Minimum Deco dives (recreational):

"Minimum Decompression - All dives require a controlled ascent (max ascent rate 30 fsw/min or 9msw/min) deep stops (starting at 65% of max ata or 50% of max depth) and minimum decompression stops (1 min @ 30fsw/9m, 1 min @ 20fsw/6msw and 1 min @ 10fsw/3msw) Example 1: A dive to 60 fsw/18msw stipulates 1 min minimum decompression stops at 30fsw/9msw, 20fsw/6msw and 10fsw/3msw. Example 2: A dive to 100 fsw/30msw stipulates deep stop pauses at 50fsw/15msw, 40fsw/12msw and 1 min minimum decompression stops at 30fsw/9msw, 20fsw/6msw and 10fsw/3msw".

 

[beester]

The study was done at recreational depths only, and the deep stops were at 1/2 the maximum depth. Those stops were then followed by a single safety stop at the standard depth. The study then essentially compared a two stop profile at reacreational depths to a one stop profile at recreational depths.

What we now call deep stops at technical depths tend to be much deeper than 1/2 maximum, and they are followed by more complex ascent profiles.

I thought the diving depth was 40m (that's what one of the testpersons told me).

 

[beester]

It's more complex, but for Rec dives it's 9m/min to 50%, then 3m/min, for tech dives at 75% is where you adjust your ascent rate from 9m/min to 6m/min (and then there are lots of other elements that determine when and what you do next).

That's the ascend procedure I follow. To 75% and slow down ascend to 6m/min (or basically 15 secs or 3 breaths on this depth, ascend to next 3m stop, repeat).

Then I'll start doing the regular 1, 2, 3 min stops based on what the buhlmann table shows (GF at 20/85 although we will adjust a bit depending on dive profile). What matters as well is the deco gasses we take with us next to 50% and or O² (21/35 or 35/25).

We don't do any mumbo jumbo on the 50%, some like S curved, others linear, we try to mimic what the deco model is saying but adjust minutes here and there to make it easy to remember. Finally on the O² I tend to try to not only do 6m but if circumstances allow have at least a 3rd of the O² time at 3m.

Above depends also on if it's pure OC or if it's mixed team (last bigger dives were really mixed... 2 OC divers, 1 RB80 and 1 JJ).

 

[beester]

Below the abstract of the scientific research on pulmonary O² damage I took part in (as guinea pig)

"
Vergelijking tussen de verandering in de Vitale capaciteit en de expiratoire “Volatile organic compound”
concentratie ter detectie van oxidatieve longschade na hyperbare zuurstofblootstelling: een experimenteel
onderzoek"
Melissa Vermeulen

Universitaire Promotor: Prof. Dr. B. Nemery
Co-promotor: Dr. Pieter-Jan van Ooij* *Hoofd Duikmedisch Centrum Koninklijke Nederlandse Marine


Abstract
The goal of this research is to compare the different methods of detecting oxidative lung damage in a experimental fashion.
Oxidative stress is defined as the collective effect of Reactive Oxygen Species (ROS) on biological molecules. Oxidative stress causes damage at deoxyribonucleic acid, lipids and proteins.
The degree of pulmoary oxygen intoxication depends on the partial oxygen pressure, the duration of the exposure and the interindividual sensitivity.
Oxygen intoxication appears mostly during saturation diving, compression tank treatment, multiple dives with an oxygen rich breathing gas mixture or the use of high levels of oxygen during decompression stages.
Exposure to high oxygen concentrations causes a diminished diffusion capacity and volume of the lungs.
Symptoms of pulmonary oxygen toxicity retrosternal pain, pain on the lungs during deep inspiration, tickling cough, dyspnea d’effort, chest tightness and apnea. With oxidative lung toxicity, a decreased vital capacity (FVC) occurs. This diminish increases with the duration of the oxygen exposure. Research of Van Ooij et al. has demonstrated that the change of FVC has a worse predictive value for submerged exposure to oxygen than for dry hyperbaric oxygen exposure.
Thereof the use of this as a means of detecting oxidative lung damage in (professional) divers is not ideal. To date, the FVC is still considered the golden standard to detect oxidative lung damage.
Volatile organic compounds (VOC’s) are small molecules, waste products of larger biomolecules, of which the partial evaporation leads to a balance between the concentration in the air and the concentration in a solid or liquid. VOC’s can be used to monitor lung cancer, asthma, inflammatory lung disease, COPD and allergic bronchitis.
The average person has 204 different VOC’s in his exhalation. During oxidative stress the destruction of lipid peroxides occurs in the cell membranes. This results in n-pentanes and Methyl Alkanes which can be measured in the exhaled air.
Malondialdehyde (MDA) is a final product of the oxidative destruction of polysaturated fatty acids. It’s a very sensitive but little specific marker for oxidative stress.
Experimental research
17 test subjects (divers) performed a ‘wet’ dive at a depth of 15 m with a bottom time of 120 min. and a breathing gas with PO2 1,56.
Two times blood was taken (60 min. before and 30 min. after the dive). Also five times FVC measurements and VOC collections were performed (60 min. before and 30, 60, 90, 120 min. after the dive).
Conclusion
This research has shown significant difference in concentration, before and after the dive, of three endogenous VOC’s: 2,3-dimethy-Butane, 2,4-dimethyl-Heptane and 2-methyl-1-Butanol.
Blood analysis shown no significant change in MDA, before and after the dive.
Probably no oxidative damage has occurred.
FVC shows a relevant rise 90 min. after the dive and VOC concentrations were significantly lower from 30 min. after the dive.

 

[boulderjohn]

I thought the diving depth was 40m (that's what one of the testpersons told me).

I am not sure what your point is. I said the test was done at recreational depths. Isn't 40m considered to be the limit of recreational depths?

 

[beester]

I am not sure what your point is. I said the test was done at recreational depths. Isn't 40m considered to be the limit of recreational depths?

Yes of course, I don't know why I had in my head 30m when you said recreational depths. I stand corrected.

I understand that the methodology of the test (recreational depths) makes the results less than optimal for "our" kind of diving (talking full trimix, T2 kind of dives). But there is not much out there that does. The NEDU tests are I believe are also not relevant enough because they are air dives with a much different profile than what I normally do on T2 dives. (see above for my normal ascend strategy).

 

[Dr Simon Mitchell]

I am not sure what your point is. I said the test was done at recreational depths. Isn't 40m considered to be the limit of recreational depths?

Hello John,

I think you and Beester are mixing up two studies. There was an Italian study of a single deep stop at ~half max depth on recreational air dives with venous gas emboli as the outcome measure. That study was published some time ago. I think that is the one you are referring to John.

There is a second study recently run in Italy in technical dives using ratio deco vs a GF approach with less deep stops. I think this is the one that Beester is citing. That study is complete but not published. Hopefully it will come out soon. No disrespect to Beester, but the claim that deep stops worked for some divers but not others is premature, and I would urge everyone to wait for the study to be properly described and published by the scientists who conducted it before discussing the results.

Simon M