Altitude after diving.

[Wijbrandus]

How does one figure out the safe interval after diving at altitude to cross the mountains going home?

For example, I perform some shallow dives at 6000 ft, and leave the location after a 2 hr SI. Then I cross a peak at 11000 ft about 4 hrs after leaving the water. Should I be increasing the interval?

Are there even guidelines on this?

 

[Charlie99]

Are there even guidelines on this?

Not a lot.

NOAA dive planning forms include a table of delay-before-ascent for 1000' increments of altitude increase. You enter the form with the USN/NOAA ending dive repetitive group.

NOAA has a disclaimer saying that the table is only good for altitudes less than 10,000'. Also, Bruce Wienke, "Mr RGBM", has stated that RGBM is more conservative in handling altitude than is the USN/NOAA calculation. So the table is probably on the agressive side of things.

Ignoring the 10,000' disclaimer for a moment, NOAA would require a 1h12m SI for 5,000 altitude increase if starting from PG E, and 3:34 if from F.

Were your dives at sea level, a 40', 50 minute dive would put you into F, as would a 40 minute dive at 50'.

I don't have the altitude correction table handy, but using a simple depth correction of 4%/1000', those would correspond to 32' 50 minutes, or 40' 40 minutes for pressure group F at your 6,000 foot altitude.

Hopefully, your "shallow dives" are of that sort of depth/time or less.

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In your favor, your ascent is probably gradual rather than the rapid ascent assumed by NOAA.

 

[Wijbrandus]

Hopefully, your "shallow dives" are of that sort of depth/time or less.

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In your favor, your ascent is probably gradual rather than the rapid ascent assumed by NOAA.

Well, we did a 40' dive for 23 minutes (adjusted to 50), a 25 minute SI, and a multilevel to the same depth and then staged it up to one level for a total of 20 minutes.

My ending was J. There was about two hours of cleaning up involved, and then it actually took me about five hours after that to hit the pass.

By that table, I should not have hit the pass. :11: I think next time I'll take the long way home that doesn't involve a mountain pass.

On the other hand, all of our LDS shops go to this location, and there has only been one DCI that they have told us about in the last few years.

I do appreciate the link. I will certainly keep that table in mind.

 

[Charlie99]

It's not surprising that you have only heard of one DCI case.

Square level tables are conservative if your actual profile is multilevel or at least not all at the table depth.

A gradual ascent gives more fudge factor.

Even if you are a bit beyond table limits, the risk increases smoothly --- it isn't a case of "one step beyond the line and you'll be bent for sure". Conversely, staying just within the limits is by no means a guarantee of not being bent.

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Taking the long way home may increase your total risks --- not from DCS, but from that car accidents

EAN40 would give you extra margin, and might be less hassle than the detour.

 

[Wijbrandus]

Well, next time I dive that location I should be nitrox certified. I think the EAN40 would be just fine there. The depth is only 65'.

I really like the safety factor that EAN provides. I think once I'm trained on it's use that will be the only gas I dive at altitude.

 

[roakey]

On the other hand, all of our LDS shops go to this location, and there has only been one DCI that they have told us about in the last few years.

Where are you talking about? Can't be Blue Hole, both Blue Hole and Raton Pass aren't that high...

Fremont Pass out of Leadville's that high, but the lakes aren't that low...

So you got me

Roak

 

[sirensmyst]

Yea...what pass is 11,000'? We have a pass at 4,000' and actually had a dcs case. Surprized us all. Get Nx certified....and be careful.
nremt/dmt

 

[Dr Deco]

Hello Readers:

Instead of the long way home, it is also possible to wait. However, one should be careful to avoid strenuous activity in that case. You can't get into too much trouble sitting in a car, but playing volleyball while you wait would certainly be a way to increase the tissue microbubbles that could form following a dive. :11:

Dr Deco :doctor:

 

[roakey]

Yea...what pass is 11,000'? We have a pass at 4,000' and actually had a dcs case. Surprized us all. Get Nx certified....and be careful.
nremt/dmt

Well, for my Denver buddies that dive Turquoise and Twin Lakes, they have to go over Fremont Pass on the way home...

http://www.myelitis.org/ridetherockies/photos/ride_the_rockies/images/image012.jpg

And there's always Independence Pass at about 12,100:

http://mysite.verizon.net/vze47hqb/sitebuildercontent/sitebuilderpictures/the_divide2_800.jpg

To name a couple...

Roak

 

[flw]

..... and it's not a terribly bright idea to spend the time soon after a dive shifting the J cylinders around to save rental either

Actually I've got an 8 day dive trip coming up and my flight home is 7am the next day, so I think it's a brilliant excuse to find someone else to do the unloading and freighting