Elevation after diving

[boulderjohn]

It feels to me that there should be some way to use current SurfGF to calculate acceptable elevation? Since that is a real time view of nitrogen loading.
Unless I'm not thinking of this correctly.

I think it can be done via our current understanding of technology. The problem (again in my opinion) is that the people writing the software do not have a clear guide to follow, and they are not anxious to be sued when someone gets bent following an algorithm that does not have a firm theoretical base.

I contacted Shearwater about this years ago, ad their response was that I should follow standard rules about flying after diving before ascending to altitude. It would be easy for them to make minor adjustments to their software to handle this, but I got the strong sense they are afraid to do so.

Another thing they could easily do is allow for different breathing gases during surface intervals. NOAA used to have guidelines for how pressure groups changed during a surface interval when breathing pure oxygen. It should be easy to set up a computer so you can change gases during a surface interval, just as you do under water. Where my friends and I did in New Mexico, the altitude is about 4,640 feet, and we regularly pack up after our last dive and head home over mountain passes reaching as high as 7,800 feet. As we drive, some of us (including me) breathe pure oxygen to lower our nitrogen levels. It would take very little software change to calculate that. As it is now, we are just guessing.

 

[inquis]

It feels to me that there should be some way to use current SurfGF to calculate acceptable elevation? Since that is a real time view of nitrogen loading.
Unless I'm not thinking of this correctly.

SurfGF is not shown when tissue loading is below ambient (which happens within a few hours of most dives). After that, there's nothing really to go on.

A Duke Univ. study in 2002 did a 55 min dive to 60 fsw, then took people up to 8000 ft elevation (commercial flight equivalent pressure) after various intervals. 8% of the divers were bent after 3 hrs, and none were bent after 11 hrs. SurfGF in both cases would have shown 0, so again, not much use.

To my knowledge, the Navy ascent tables are about the best guide available for this sort of thing.

 

[Kendall Raine]

I can't find anything in the Manual that says that. How do you know?

Think about it. Seriously.

 

[broncobowsher]

FWIW, the Sepulveda Pass in LA is more than 1,000 feet and people routinely drive it after even somewhat aggressive Tec dives. There's just no other way to get to the San Fernando Valley from the boats.

Coming out of San Diego heading East is a 5000' pass before dropping back down to the Colorado river valley. Coming off the dive boats, loading gear up, getting a bite to eat then it is a slow gradual climb.

Also add in, look at the remaining tissue loading (great feature with a shearwater) in the morning after several days of tech diving. Barely a blip on the slowest tissues.

Guidelines are based on absolute worst case conditions for the simplicity of not having choices.

 

[rjack321]

I can't find anything in the Manual that says that. How do you know?

These divers are in the NAVY

How do you expect them to get to altitude?
Walk on water and then mountain climb?

 

[Searcaigh]

Avoiding bends is always a good idea. The Navy tables were tested with subjects going to altitude at aircraft climb rates (~2,000 FPM). Not driving. Besides, unless you go early you’re likely to encounter lots of Bali traffic making your driving ascent rate even slower. ;-).

Ascent rate is the key.

When I dive on the east coast of the UAE we have some mountains to negotiate on the way back to Dubai, and maximum altitude is around 600m (1,968ft) above sea level.

Generally we don't set off until after lunch post two dives, in the region of two-three hours after surfacing. Maximum altitude of 600m is achieved at 15-20 mins depending on traffic, which equates to around 40m (131ft) per minute at the faster rate.

Pressure difference in air though is less than in water and I used this site to calculate the change which equates to 1 bar => 0.93 bar which I would say is rather insignificant.

 

[CycleCat]

Ascent rate is the key.

Exactly. The OP is riding a bicycle to 2000 feet. Given the SI since the previous day's dive, the slow rate of ascent using pedal power, and the aerobic breathing he is going to be doing to get there, I'd say he's not going to get bent.

 

[chillyinCanada]

OP should feel free to correct me if I'm wrong, but my understanding is that there will be a car ride up the mountain before the bike ride at altitude.

Starting off at sea level, how long in the vehicle before attaining any altitude? OP, how long from vehicle pickup until expected bike ride begins?

 

[Kendall Raine]

These divers are in the NAVY

How do you expect them to get to altitude?
Walk on water and then mountain climb?

Zactly. Testing protocols described in attached. Ascent rate =2,000 FPM.

 

[BabyLitigator]

Coming out of San Diego heading East is a 5000' pass before dropping back down to the Colorado river valley. Coming off the dive boats, loading gear up, getting a bite to eat then it is a slow gradual climb.

Also add in, look at the remaining tissue loading (great feature with a shearwater) in the morning after several days of tech diving. Barely a blip on the slowest tissues.

Guidelines are based on absolute worst case conditions for the simplicity of not having choices.

Fair. My tissues ‘cleared’ a few hours after my last Tec dive. Got a great big warning on the shearwater (software update). No diving this week or altitude so presume fine