Driving to altitude after diving

[Thalassamania]

Divers are used to the idea that the greatest pressure change is near the "top." In the atmosphere, because it is compressible, the opposite is true, the greatest percentage change is at low altitude and it is less higher up.

A diver who is in H and goes to 3000 feet, with the first 1000 feet being right away, has a potential for problems, especially if the dives that put him in H were shallower, longish dives as opposed to deeper, short dives ... not all H divers are the same, once you go to a letter group you lose any information about slow vs. fast tissues.

 

[ChristyV]

Thanks!

 

[amascuba]

Divers are used to the idea that the greatest pressure change is near the "top." In the atmosphere, because it is compressible, the opposite is true, the greatest percentage change is at low altitude and it is less higher up.

A diver who is in H and goes to 3000 feet, with the first 1000 feet being right away, has a potential for problems, especially if the dives that put him in H were shallower, longish dives as opposed to deeper, short dives ... not all H divers are the same, once you go to a letter group you lose any information about slow vs. fast tissues.

Good point.

 

[ChristyV]

I didn't know that. Thanks for that information.

 

[Wayan]

I have never really worried a lot about it but recently I was told by a dive shop that I could not make a one hour night dive to "about" 45 ft off shore with them unless I had a place to stay down there. They were pretty adamant about the "danger." I have many many times done well over an hour single dive at that beach and gotten home within two hours. Their attitude made me think I take the whole thing too lightly. P.S. I am a (non-teaching) PADI certified instructor.

Current DAN recommendations after the Flying after diving workshop
apply to air dives followed by flights at cabin altitudes of 2,000 to 8,000 feet (610 to 2,438 meters) for divers who do not have symptoms of decompression sickness (DCS). The recommended preflight surface intervals do not guarantee avoidance of DCS. Longer surface intervals will reduce DCS risk further.

* For a single no-decompression dive, a minimum preflight surface interval of 12 hours is suggested.
* For multiple dives per day or multiple days of diving, a minimum preflight surface interval of 18 hours is suggested.
* For dives requiring decompression stops, there is little evidence on which to base a recommendation and a preflight surface interval substantially longer than 18 hours appears prudent.

What must be remember that these figures come from controlled dives in a Hyperbaric Unit, so a number of factors are not involved in this process such as cold, exercise...etc.

Some divers will plan their dives as being at altitude and reason that the dive will be somewhat more conservative than it otherwise would have been which is true, however the dive will still likely result in some degree of bubble formation. What happens to these bubbles on ascent to altitude is still very highly unpredictable.
I believe that there was some testing of this strategy which found an unacceptably high rates of DCI and it was not recommended.

So it is wise to impose an delay after diving before ascending to altitude and you find a lot of Hyperbaric/Diving Specialists Doctors agree that is hard to put a time on it to say exactly how long is okay before you are able to go to altitude with out risk

Best advice is always be conservative

 

[Gene_Hobbs]

What must be remember that these figures come from controlled dives in a Hyperbaric Unit, so a number of factors are not involved in this process such as cold, exercise...etc.

Just to add to this, the last (calibration) phase of the trials are underway now and do look at the effects of immersion and exercise. So far we have seen no reason to change the model based on the results but the trial is ongoing.

**We need subjects if anyone lives close to Duke (Durham, NC).

Some of you might also be interested in our "suggested reading list" on this topic.


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