Nitrox and Altitude

[leabre]

I'm NAUI Nitrox Certified. We have a wheel that gives us an equivelant air depth (EAD). I also have a NAUI device that, given an altitude and depth, gives you an equivelant depth for that altitude (and fresh water).

I do not have NAUI Nitrox altitude tables because in Southern California they would be nearly pointless.

But I do plan to dive altitude in the near future and was wondering if it is enough to calculate EAD and then that that depth and use it for altitude calculations or if I actually must have altitude tables (for technical reasons, rather than convenience). I searched through the NAUI Nitrox book and it really only mentions using altitude Nitrox tables, but mentions nothing about whether I can use the EAD with the altitude adjustment device (have no idea what it is called).

Further, I couldn't find anything specific in the PADI Nitrox book, either.

Would anyone here know the answer?

 

[Tortuga68]

It's covered in the PADI AOW manual

1. If you're diving within 6 hours of arriving at altitude (300m - 3000m or 1000' - 10000') you need to adjust your starting pressure group

2. You need to adjust actual depth to theoretical depth - there's an imperial chart here Hoofers SCUBA - Club Protocols & Safety or you can google a metric one

3. Be aware that your SPG reading may also need to be adjusted up or down depending on whether it's Bourdon tube or capilliary

Once you've done that you should be able to just use the EAD for nitrox I think, and calulate your NDLs from there

You should also adjust your descent/ascent rates and safety stop levels accordingly (although actually the latter hardly changes within rec limits), and it's suggested not to do more than two repetitive dives per day & no deeper than a theoretical depth of 40m for recreational dives

Don't forget to adjust your weight/bouyancy to compensate for fresh water/altitude as well

Oh, and your No Fly time after diving will be longer too

HTH, did I miss anything guys?

 

[knotical]

Bravo for knowing that whatever techniques you use, you should adjust both for altitude and for Nitrox.

Calculations without tables should be OK. But tables can be more convenient.

Did you realize the effects tend to cancel? http://www.scubaboard.com/forums/2198370-post79.html

 

[rstofer]

This article might be useful: Startin' with Scuba: Diving at altitude revisited

Richard

 

[fdog]

It's covered in the PADI AOW manual

1. If you're diving within 6 hours of arriving at altitude (300m - 3000m or 1000' - 10000') you need to adjust your starting pressure group

2. You need to adjust actual depth to theoretical depth - there's an imperial chart here Hoofers SCUBA - Club Protocols & Safety or you can google a metric one

3. Be aware that your SPG reading may also need to be adjusted up or down depending on whether it's Bourdon tube or capilliary

Once you've done that you should be able to just use the EAD for nitrox I think, and calulate your NDLs from there

You should also adjust your descent/ascent rates and safety stop levels accordingly (although actually the latter hardly changes within rec limits), and it's suggested not to do more than two repetitive dives per day & no deeper than a theoretical depth of 40m for recreational dives

Don't forget to adjust your weight/bouyancy to compensate for fresh water/altitude as well

Oh, and your No Fly time after diving will be longer too

HTH, did I miss anything guys?

Shorter, actually. He's already at altitude.


Leabre, although I use computers or V-Planner, if I had to do it manually I'd do exactly what you suggest, calculate EAD and altitude conversion tables.

As Tortuga68 so rightly points out, altitude conversion of the depth gauge is very often overlooked.


All the best, James

 

[scubajb]

Great question! I have a related one. I live at altitude, approximately 5000 - 6000 feet. We dive higher altitude mountain lakes all the time with altitude diving procedures. There are NO dive shops in the state that recommend diving Nitrox at these altitudes. Most of the objections deal with the little research that has been done - and little demand as well. Specifically, one shop cites research indicating the increased incidents of silent bubbles. Any thoughts? Have their been recent research relating to Nitrox and altitude?

Jim

 

[fdog]

Great question! I have a related one. I live at altitude, approximately 5000 - 6000 feet. We dive higher altitude mountain lakes all the time with altitude diving procedures. There are NO dive shops in the state that recommend diving Nitrox at these altitudes. Most of the objections deal with the little research that has been done - and little demand as well. Specifically, one shop cites research indicating the increased incidents of silent bubbles. Any thoughts? Have their been recent research relating to Nitrox and altitude?

Jim

Fascinating. I would be agog with curiosity to read this research - virtually every study I've read (and participated in, during the 70's, including investigations at Lake Tahoe) had a decrease in bubbles from Nitrox use.

We dive Lake Tahoe (6300') several times a week using nitrox. Next week we'll be putting in about 50 miles underwater - again, using 32%. I would use nitrox in any situation where I wanted to reduce my nitrogen obligation, regardless of altitude....I suspect that the lack of support for nitrox in your area may have more to do with the "PITA factor" for the shop.


All the best, James

 

[scubajb]

Agree completely about reduction in nitrogen uptake. Seriously doubt I will be able to change nitrox practices up here but I would like to base it on research. Now if my wife would only get off her butt and get a second job and buy some EAN mixing and supply equipment... Thanks for the info. Maybe we'll get out to Tahoe sometime and go splash!

 

[rstofer]

Fascinating. I would be agog with curiosity to read this research - virtually every study I've read (and participated in, during the 70's, including investigations at Lake Tahoe) had a decrease in bubbles from Nitrox use.

We dive Lake Tahoe (6300') several times a week using nitrox. Next week we'll be putting in about 50 miles underwater - again, using 32%. I would use nitrox in any situation where I wanted to reduce my nitrogen obligation, regardless of altitude....I suspect that the lack of support for nitrox in your area may have more to do with the "PITA factor" for the shop.


All the best, James

James,

My wife and son-in-law are taking a couple of specialties this week at Lake Tahoe. The deep specialty will be on the order of 60' with no particular intention to go much deeper. For this, they will be using air so MOD won't be a limiting factor regardless of the depth (assuming it could reach, maybe, 100').

For the navigation specialty, depth could be somewhat less (I hope) and they are taking 6 HP100s full of EAN36 because that's what's in the tanks.

They will both be using Dive Rite Nitek Duo's which compensate for alititude, fresh water and nitrox mixture. So their NDLs should be pretty accurate and, I suspect, they won't even come close.

Sand Harbor will be the dive site.

What do you think?

Thanks
Richard

 

[fdog]

Richard, that would be fine. Right now, with the lake level being so low, you have to swim a loooong way at Sand Harbor to get much deeper than 25'.

I wouldn't worry about using air for the deep dive, I'd happily take 36% to 100' at the lake, and it's actually a good use for it.

And the Duo is a good computer, it will do a great job.

Enjoy Sand Harbor! The Lake will be a nice relief from the heat, too.


All the best, James