Dr Deco
Contributor
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- # of dives
- I just don't log dives
Hello Readers:
This has been written as a response to the Forum on “Shallow Diving and Flying.”
I have spent parts of several days reading the workshop proceedings on diving and flying as well as a recent paper in Aviation Space and Environmental Medicine. My conclusions are the same as the panel who investigated this before – it is a can of worms.
Based on laboratory science, for most recreational dives, only a few hours surface interval is needed. In DAN’s experience, however, DCS problems have occurred despite what lab tests indicate. This is probably for the reasons indicated below. Twelve to 24 hour hours is really what is recommended – still.
The problem, as I can tell it, is that there are a couple of situations that are interconnected. Some colleagues and I looked at this question when I was at NASA since astronauts who trained in a neutral buoyancy pool also went flying afterwards. We did not find a clear pattern.
Chaotic and Non-Linear Processes
Diving is in 99.99% of the cases a “chaotic” event as viewed in terms of physical processes. This means that small variation in the process can result in quite different results. Certainly, we might concede that all divers are different in their decompression characteristics. This can be demonstrated in laboratory tests. Recreational [and technical] divers will not know their “DCS tendency” without some test – or only after every extensive dive experience. [If they “dodge the bullet” often enough, they might guess that they are DCS-resistant divers.]
However, in this case, we are describing differences in degree of musculoskeletal activity [= tissue micronuclei formation]. In tests of dive tables, this is controlled somewhat since all of the test subjects come into the lab, sit for a while, are compressed [or depressurized], perform some planned activity, surface, and sit while the Doppler monitoring period continues.
This “choreographed activity” is not what occurs during real life dive scenarios. There will then be place into the system random variables. The tendency towards micronuclei formation is a large variable. Sometimes small activities [e.g. straining or lifting] can have a large effect on the number of nuclei.
Non Linear System
When the nuclei form, the off gassing is changed in a way that is not predicted by the table developers. There is actually no way to model it since it is dependent on many factors, e.g., geometry of the tissue and bubbles. Systems that continually change with feedback as they proceed are non linear.
Fly After Diving
Now, we add to the problem of ascent [depressurization] the complication that some divers may be harboring bubbles in their tissues. One can see how this now is a second problem to simply determining residual tissue nitrogen. When DCS "hits" are found that occur 10 hours after diving, it is clear that this is most likely a residual bubble problem and not one of residual nitrogen.
Dr Deco :doctor:
This has been written as a response to the Forum on “Shallow Diving and Flying.”
I have spent parts of several days reading the workshop proceedings on diving and flying as well as a recent paper in Aviation Space and Environmental Medicine. My conclusions are the same as the panel who investigated this before – it is a can of worms.
Based on laboratory science, for most recreational dives, only a few hours surface interval is needed. In DAN’s experience, however, DCS problems have occurred despite what lab tests indicate. This is probably for the reasons indicated below. Twelve to 24 hour hours is really what is recommended – still.
The problem, as I can tell it, is that there are a couple of situations that are interconnected. Some colleagues and I looked at this question when I was at NASA since astronauts who trained in a neutral buoyancy pool also went flying afterwards. We did not find a clear pattern.
Chaotic and Non-Linear Processes
Diving is in 99.99% of the cases a “chaotic” event as viewed in terms of physical processes. This means that small variation in the process can result in quite different results. Certainly, we might concede that all divers are different in their decompression characteristics. This can be demonstrated in laboratory tests. Recreational [and technical] divers will not know their “DCS tendency” without some test – or only after every extensive dive experience. [If they “dodge the bullet” often enough, they might guess that they are DCS-resistant divers.]
However, in this case, we are describing differences in degree of musculoskeletal activity [= tissue micronuclei formation]. In tests of dive tables, this is controlled somewhat since all of the test subjects come into the lab, sit for a while, are compressed [or depressurized], perform some planned activity, surface, and sit while the Doppler monitoring period continues.
This “choreographed activity” is not what occurs during real life dive scenarios. There will then be place into the system random variables. The tendency towards micronuclei formation is a large variable. Sometimes small activities [e.g. straining or lifting] can have a large effect on the number of nuclei.
Non Linear System
When the nuclei form, the off gassing is changed in a way that is not predicted by the table developers. There is actually no way to model it since it is dependent on many factors, e.g., geometry of the tissue and bubbles. Systems that continually change with feedback as they proceed are non linear.
Fly After Diving
Now, we add to the problem of ascent [depressurization] the complication that some divers may be harboring bubbles in their tissues. One can see how this now is a second problem to simply determining residual tissue nitrogen. When DCS "hits" are found that occur 10 hours after diving, it is clear that this is most likely a residual bubble problem and not one of residual nitrogen.
Dr Deco :doctor:
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