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jeff baird
07-24-2010, 11:06
I'm a trk driver that lives in the Dallas area, and run back and forth to CA. , I have been carrying my gear, and stop about once a week and dive blue hole in Santa Rosa NM.
Blue Hole is 4600 feet in altitude, and 80' deep,, When I dive there I do not have the time to aclimate to the altitude, I have been adding 14' to the depth and doing a decompession stop at 15', and have not had any trouble, and note I usually only do 1 dive.
Question,,,,, Within 7 hours of me leaving Blue Hole, I cross a mountain pass that is at 8000 feet in altitude,, after talking to another diver he seems to think I should adjust tables to to highest altitude that I will cross within hours of diving, which would 8000' ,,, and I believe that adds approx 26' to tables and change decom. stop to around 12'.
There are days I have time to do a 2nd dive, but have been a little confused on tables for altitude, any info would be appreciated......... thanks jeff

comet24
07-24-2010, 13:27
I don't have much experience diving at altitude but know you shouldn't dive and then travel to a higher altitude. Kinda like diving and flying. DAN should have some info on this.

SlvrDragon50
07-24-2010, 13:46
I would avoid diving and high altitudes as much as possible but I think you can still do it safely.

In 7 hours SI, most people return to group A (don't have tables on hand to be sure). Just exactly what are you having trouble with?

Just add 26' to your depth and then adjust accordingly. I'd be a bit more conservative and go 30'.

scubastud
07-24-2010, 14:23
Got me thinking, do computers factor in altitude ? Some of them.. all of them none?

SlvrDragon50
07-24-2010, 15:06
My Nitek does. There are "Conservative Levels" - SF0,SF1,SF2 - which you set according to altitude or if you just wanna be conservative.

Chilly
07-24-2010, 20:56
I'm a trk driver that lives in the Dallas area, and run back and forth to CA. , I have been carrying my gear, and stop about once a week and dive blue hole in Santa Rosa NM.
Blue Hole is 4600 feet in altitude, and 80' deep,, When I dive there I do not have the time to aclimate to the altitude, I have been adding 14' to the depth and doing a decompession stop at 15', and have not had any trouble, and note I usually only do 1 dive.
Question,,,,, Within 7 hours of me leaving Blue Hole, I cross a mountain pass that is at 8000 feet in altitude,, after talking to another diver he seems to think I should adjust tables to to highest altitude that I will cross within hours of diving, which would 8000' ,,, and I believe that adds approx 26' to tables and change decom. stop to around 12'.
There are days I have time to do a 2nd dive, but have been a little confused on tables for altitude, any info would be appreciated......... thanks jeff

Brother,

I want you to dive safely, but I think you are speeding here. You may think you are doing only one dive at altitude, but without equilibration and acclimatization you are essentially doing a repetitive dive profile - your first dive was the ascent from sea level to altitude.

To answer your original question, ascending after a dive requires a new surface interval determination based on your repetitive group designator and the altitude increase you desire. Ref the following table from the USN Dive Manual Rev 6:

7418

Note that when you ascend to 8000' MSL you are essentially flying. The basic DAN guidance is a 12 hr surface interval prior to flying with additional restrictions based on your dive profiles.

I highly recommend that you take a high altitude diver course and consider purchasing a dive computer that you know specifically adjusts for altitude and become familiar with how it accomplishes this adjustment.

Welcome to the Forum Jeff! Hope this helps.

BubblesMcCoy
07-25-2010, 11:58
Jeff,
I started looking into this issue when some buddies and I began diving Santa Rosa a couple of years ago. I agree with Chilly in that your profile is worrisome. Adjusting your table depths to calculate your NDC is a good start, but doesn't take into account for the significant pressure/altitude change during your trip west. My limited understanding is that the issue is that any residual nitrogen in your bloodstream could come out of solution (form bubbles) much faster as you increase in altitude.

Again, to my limited understanding, the risk you are taking that you'll develop a DCS hit after the dive is over and as you are driving to a higher altitude. I've read anecdotal stories of this type of thing happening to private pilots who didn't fully offgas before flying. Thus, DAN recommends that you off-gas before you fly. Given that driving to a higher altitude is probably not too different, I would imagine the same recommendations would apply.

The instructors experienced with Santa Rosa that we discussed the issue with told us that we were likely fine as we dive, then head east to a lower altitude. We stay the night anyways and have never pushed that issue, but if you can do your dives on the return trip east it might reduce some of the risks.

I'm not sure how a dive comp will help you with the issue of post dive altitude, but we dive altitude adjusted computers and its makes the adjusted depth calculations much easier and more precise. Although Blue Hole isn't as high as some places, the difference in NDC limits is significant given the depth and temp of blue hole.

Dive safe.

inventor
07-25-2010, 12:20
My instructor told of a student that went deep diving in Cali, and directly after the dives started driving to Las Vegas. In coming over the pass, he got bent badly, and managed to pull over. However he did get some kind of damage, as I recall. I wouldn't think it's worth the risk, but it is worth a call to DAN.

fire diver
07-25-2010, 14:22
There is a lot of guessing and conjecture going on here.

Do an internet search for the altitude conversion for the alt at the BH. IIRC you are pretty close in what you are doing already. Adding that extra conservatism, and doing an extended stop in the 15-10 foot range is plenty for safety.

Everyone seems to be getting wrapped around the axle (so to speak) about the change in altitude and equating it with flying. Thew danger in altitude change in flying is that the plane goes up from ground level in a matter of seconds. SEcondly, if the plane depressurizes then that is another huge change in a matter of seconds. DRIVING from the Blue Hole, over a mountain pass at 8000 feet hours later is simply nothing to worry about. The slow change in atmospheric pressure is far, far slower than the change in pressure during even the slowest diving ascent.

Think about a pop bottle. You can open a bottle quick, and be fine. Shake it up, open it quick and you are in trouble. Shake it up, open in slow and you are fine too. The same mechanics is happening in your body.

Another way to look at it... you go from 30ft to the surface in a matter of minutes. That is changing from a pressure of ~30psi to 15psi (IN MINUTES). Then changing from 15psi to 12 psi IN HOURS. (12psi is roughly the pressure at 8000 feet). Since you are starting at ~4000 feet, the change is even smaller.

fire diver
07-25-2010, 14:36
My instructor told of a student that went deep diving in Cali, and directly after the dives started driving to Las Vegas. In coming over the pass, he got bent badly, and managed to pull over. However he did get some kind of damage, as I recall. I wouldn't think it's worth the risk, but it is worth a call to DAN.


I've found that instructor tend to lie or re-tell stories from other instructors as if it was thier own student. Talk to the diver in question, personally, before you believe the story.

Chilly
07-25-2010, 18:26
There is a lot of guessing and conjecture going on here.

Do an internet search for the altitude conversion for the alt at the BH. IIRC you are pretty close in what you are doing already. Adding that extra conservatism, and doing an extended stop in the 15-10 foot range is plenty for safety.

Everyone seems to be getting wrapped around the axle (so to speak) about the change in altitude and equating it with flying. Thew danger in altitude change in flying is that the plane goes up from ground level in a matter of seconds. SEcondly, if the plane depressurizes then that is another huge change in a matter of seconds. DRIVING from the Blue Hole, over a mountain pass at 8000 feet hours later is simply nothing to worry about. The slow change in atmospheric pressure is far, far slower than the change in pressure during even the slowest diving ascent.

Think about a pop bottle. You can open a bottle quick, and be fine. Shake it up, open it quick and you are in trouble. Shake it up, open in slow and you are fine too. The same mechanics is happening in your body.

Another way to look at it... you go from 30ft to the surface in a matter of minutes. That is changing from a pressure of ~30psi to 15psi (IN MINUTES). Then changing from 15psi to 12 psi IN HOURS. (12psi is roughly the pressure at 8000 feet). Since you are starting at ~4000 feet, the change is even smaller.

Zero guessing or conjecture for determining the SI for Ascent to Altitude After Diving / Flying After Diving - Only procedure IAW USN Dive Manual Rev 6. No difference between flying or driving to altitude in this procedure.

Other agencies may have different procedures. If so, I hope someone can share with us.

Bottom line - get the training, follow the guidance, know how to manage the risk of DCS when diving at altitude. Don't guess.

fire diver
07-25-2010, 19:45
There is an order of magnitude in difference between flying and driving to altitude.

mitsuguy
07-26-2010, 21:01
In general, all of the flying and altitude change recommendations are super conservative...

If we want to talk about theory and pressures, we sure can...

here's a bit of disagreement, even in PADI's tables - regardless of what your profiles for all consecutive dives were, so long as you stayed within the tables limits (no-deco), after a 6 hour surface interval, you are considered a "fresh" diver with no nitrogen, and the next dive should be calculated as a first dive. However, if you did multiple dives, you are required to have an 18 hour surface interval, per PADI's tables...

We could also do all sorts of math about ascents and pressure changes, but, the example mentioned already was ascending from 30 feet to the surface in a matter of minutes, but in all honesty, according to PADI's tables, a 60 fpm ascent rate is perfectly ok, and so long as a safety stop is not required, you can make it to the surface in 30 seconds, within the guidelines of PADI's tables... One note about this though - when diving at altitude, a maximum ascent rate of 30 fpm is recommended...

So, a computer that adjusts for altitude is great for all of this because you don't have to worry about the depth adjustments, however, there isn't a computer out there that will adjust for a higher altitude by itself - you would have to set it for a higher altitude specifically, prior to the dive, as they have no way of knowing beforehand...

I would imagine the reason that there is no difference between flying and driving to altitude is that there are so many different speeds that you could arrive at a higher altitude depending on how steep the highway is and such...

here's what PADI says about this:
"If students arrive at an altitude dive site that is higher than their
point of origination they must either:
1. Wait 6 hours prior to making their first open water altitude
dive, OR
2. Count two pressure groups for each 300 metres/1000 feet of
altitude to determine their beginning pressure group (round
up fractions of 300 metres/1000 feet.
When diving above 2400 metres/8000 feet, students must wait 6 hours
prior to making an open water dive."

PADI's recommendations about driving to altitude are the same as the Navy's - flying or driving to altitude, wait the appropriate times (12 hours single no-deco dive, 18 hours multiple dives, greater than 24 hours if deco time is incurred)

Playing it safe, sure, but where do you really draw the line?

Chilly
07-26-2010, 22:27
here's what PADI says about this:
"If students arrive at an altitude dive site that is higher than their
point of origination they must either:
1. Wait 6 hours prior to making their first open water altitude
dive, OR
2. Count two pressure groups for each 300 metres/1000 feet of
altitude to determine their beginning pressure group (round
up fractions of 300 metres/1000 feet.
When diving above 2400 metres/8000 feet, students must wait 6 hours
prior to making an open water dive."

PADI's recommendations about driving to altitude are the same as the Navy's - flying or driving to altitude, wait the appropriate times (12 hours single no-deco dive, 18 hours multiple dives, greater than 24 hours if deco time is incurred)

Playing it safe, sure, but where do you really draw the line?

Mitsuguy,

Thanks for providing the PADI perspective to this thread topic. In contrast, the USN equilibration period is a straight 12 hrs, else apply a table calculation for residual nitrogen.

I personally draw the line at having a procedure vice leaving my DCS risk management up to chance. USN and DAN guidelines work for me.

fire diver
07-26-2010, 23:51
Mitsuguy, you posted some good info there, but I have to make one change (I swear I'm not just arguing for the fun of it). Many computer DO automatically make altitude adjustments. I know for a fact that my computer does. The only change you have to make before dives are nitrox value (if other than 21) and sea/fresh water.

"Altitude & Depth -- The NiTek Duo automatically adjusts for altitudes up to 19,680 feet, and is capable of functioning at depths at deep as 328 feet in computer mode and 656 feet in gauge mode."