No-fly in Subsurface?

[Willem Ferguson]

On 26/07/2016 15:53, Dirk Hohndel wrote:
>> On Jul 26, 2016, at 6:16 AM, Robert Helling <helling at atdotde.de 
>> <mailto:helling at atdotde.de>> wrote:
>>
>> Hi all,
>>
>>> On 26.07.2016, at 14:30, Robert Helling <helling at atdotde.de 
>>> <mailto:helling at atdotde.de>> wrote:
>>>
>>> I haven’t had time to read in the proceedings of the DAN workshop 
>>> that was linked before. What I saw that came most closely to a 
>>> recommendation was a report of a plan to do a study trying to bend 
>>> subjects in a simulated fly after dive scenario. Which is not much 
>>> that could be put into software. Maybe one should check the Rubicon 
>>> Archive for more scientific information on the issue.
>>>
>>
>> ok, I did some Rubicon search and follow up reading an the two most 
>> relevant papers seem to be
>>
>> http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/6255/SPUMS_V9N3_4.pdf?sequence=1
>> and
>> http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/5611/DAN_FAD_2002.pdf?sequence=1
>> (in particular the executive summary).
>>
>> Upshot seems to be: Very hard to asses given the low number of cases 
>> (boarding a place when you already have DCS symptoms seems to be a 
>> totally different game, though), but 12-18h limits, maybe 24h seem to 
>> be a good idea and there is no model on the marked that is able to 
>> predict this.
>
> This seems to match my expectations.
> a) made up random shit
> b) semi-scientific algorithms, tuned by random numbers without any 
> scientific basis in order to match pre-conceived notions of "this 
> sounds about right"
>
> /D
>
Be fair, it's a hugely multidimensional problem that is not easily 
tractable. The DAN project at experimental decompression to 8000 ft had 
pretty low sample sizes but there was (if I recall correctly) one 
serious case of DCS in the order of 12 h after repetitive diving. Was it 
just a single individual response? Really part of a pattern? Difficult 
to say. I would say a first-level approach is to use the standard models 
we have and predict saturation levels when flying after various surface 
times. Question is, what cutoff level of PN2 (or bubble size) indicates 
safe flying condition? Given this lack of understanding, if a 
recreational diver, diving 6 dives a year, with no understanding of PN2 
and how to manage it, asks me this question, I would probably use the 
guess of 24h before flying. This diver does not understand the 
complexity of the problem and wants an answer. For DAN there are 
potentially real costs related to the consequences of their advice, so I 
understand their point of view.

In the past we have made extensive use of the NOAA table for 
surface-time-before-flying. But I have no idea what the basis was for 
that table and we often forget we have to take it with a pinch of salt.

Alternatively, we sometimes plan the last dive(s) to do deco as if we 
are doing the dive at the maximum altitude we will experience. I do this 
when I need to cross mountains of 2000m altitude to get home after 
waiting and additional 2 h. We have not had incidents yet, but we hardly 
have a large sample size upon which to base such a practice.
Kind regards,
willem


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