Decompression diving at altitude?

[Jim Lapenta]

The lake where we dive is not excessively deep. maybe 130 ft max. The dive area tho is more like 118 but some have reported finding a hole that goes to 127. The lake is also at 3550 ft above sea level give or take. either way it necessitates using the altitude tables which make it 4000ft for calculations. My question is this. Some of us would like to find this "hole" and dive it.Adjusted depth and time involved in locating it if it exists would require deco stops. Now I have the navy tables for decompression dives and we would be using these. Taking the altitude into acct a 118 ft dive becomes 139 ft which means using the 140 or maybe 150 depth table for added safety. Do I need to adjust the deco depths. For instance being at this altitude we do our safety stop at 13 ft rather than 15. On the 140 table first stop is at 20 next at 10 for a 30 min dive with times of 5 & 21 minutes respectively. with 2 minutes to the first stop. These are all dives that would be done on air or maybe a 28-30 % nitrox mix. times and depths would be adjusted accordingly if using nitrox while monitoring ppo levels.

 

[Jim Lapenta]

p.s. If I wanted to get the best book on deco and deco table use what would you all recommend,?

 

[knotical]

Do I need to adjust the deco depths?

Yes. As you pointed out, you need to adjust your safety stop depth. Similarly you should adjust all decompression stop depths, in order to maintain the same relative pressure ratios between the surface and your stops.

 

[Jim Lapenta]

Yes. As you pointed out, you need to adjust your safety stop depth. Similarly you should adjust all decompression stop depths, in order to maintain the same relative pressure ratios between the surface and your stops.

So in this case would it be using the 20 and 10 ft deco stops be changed to 17' and
9'?:06: These depths are taken from the Theoretical Safety/Emergency Decompression Stop Depth Table. And are there tables specifically for deco diving at altitude. I ask this because the table I have only goes to a stop at 30'(=26') and tho it's highly unlikely we would be down long enough to require a stop at 40:11: I'd just like to have the info.

 

[DandyDon]

I live at 3,300 feet and just activated my Oceanic computer for a dive plan. It reads altitude, give or take 1,000 feet, so I never know if for sure if it's reading at 2, 3, or 4,000 feet. It would allow a dive to 170 feet for 4 minutes without decompression, tho.

How long do you think you'll be at 130 feet? Not long if all of you are on 80 cf tanks. You should be able to get down, take a couple of pics, and start ascending slowly - with a one minute stop at 65 feet and minutes or more at 13 feet without going into decom.

But do make sure your computer is very happy at all times.

 

[markd_nscr986]

Are you planning on using air for your deco gas as well?

 

[ianr33]

Why not download a trial copy of V Planner www.v-planner.com It does altitude correction

At 3500 feet using 28% a bottom time of 12 minutes gives around 5 minutes of stops,only a couple of minutes more than at sea level.

What gear are you using? Personally if I am going to 130 then doubles are kinda nice. Also if you plan on incurring more than a couple of minutes of deco you may wish to consider some training in this area

 

[TheRedHead]

He would use the EAD at sea level to calculate deco. The Navy tables are not being used by deco divers these days. Find a deco planner on the net and play with it. Try Gary Gentile's Technical Diving Handbook for starters. He's also from PA.

 

[Dr Deco]

Hello JimLap:

The answer is that the stop depths are adjusted for altitude (somewhat shallower). In addition, the ascent rates are changed (somewhat slower).

Dr Deco :doctor:

 

[TheRedHead]

So in this case would it be using the 20 and 10 ft deco stops be changed to 17' and
9'?:06: These depths are taken from the Theoretical Safety/Emergency Decompression Stop Depth Table. And are there tables specifically for deco diving at altitude. I ask this because the table I have only goes to a stop at 30'(=26') and tho it's highly unlikely we would be down long enough to require a stop at 40:11: I'd just like to have the info.

See Section 9-12 of the Navy Diving Manual:

http://www.coralspringsscuba.com/usn/Chap09.pdf

Not that I personally endorse diving the Navy tables.