Can a diver safely perform the 10 FSW decompresion stop at 15 FSW without complications?
Hmmm? Tables vs computer
- Thread starter GDI
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
Caver95
Contributor
from a computer or tables?
OP
Consider Both
Charlie99
Contributor
- Messages
- 7,966
- Reaction score
- 169
- # of dives
- 500 - 999
Short version: 15' stop is fine, but you will need to hang for a bit longer.
-------
The greatest effect would be when trying to decompress with air from a very lengthy dive that has loaded the very slow tissues.
Using air, at 10' the inspired ppN2 is about 32.7fsw; at 15' about 36.7fsw. This makes a pretty significant difference when trying to offload a 43.4fsw M0 DSAT 480min compartment, (or a 43.5fsw 390 min ZHL16 compartment if you prefer Buehlmann). This is a greater than 50% increase in time for this rather unusual case.
If the limiting compartments are faster, or the use of nitrox at the stop will dramatically reduce the increase in time required.
p.s. In my post 15' means 15' depth below sea level. 15fsw would mean 15/33=0.45 atmospheres absolute pressure.
---
You can alway use a decompression program such as that found at www.gap-software.com to see the effect of stop depth. Many programs have an option "last stop depth" that lets you easily see the effect for any chosen dive profile.
-------
The greatest effect would be when trying to decompress with air from a very lengthy dive that has loaded the very slow tissues.
Using air, at 10' the inspired ppN2 is about 32.7fsw; at 15' about 36.7fsw. This makes a pretty significant difference when trying to offload a 43.4fsw M0 DSAT 480min compartment, (or a 43.5fsw 390 min ZHL16 compartment if you prefer Buehlmann). This is a greater than 50% increase in time for this rather unusual case.
If the limiting compartments are faster, or the use of nitrox at the stop will dramatically reduce the increase in time required.
p.s. In my post 15' means 15' depth below sea level. 15fsw would mean 15/33=0.45 atmospheres absolute pressure.
---
You can alway use a decompression program such as that found at www.gap-software.com to see the effect of stop depth. Many programs have an option "last stop depth" that lets you easily see the effect for any chosen dive profile.
Breath oxygen at that stop and it won't make any difference.
Running some schedules in vplanner you'll see that there isn't a noticable difference in run time even between using a 20 ft stop as a last stop and a 10 ft stop.
Obviously in this case there isn't any inert gas in the inspired gas and the only difference is in ambient pressure.
For me it means no decompression on back gas especially if it's air. As far as I'm concerned it's a good idea to have a bottle of O2 around anyway especially fi you incuring a "mandatory decompression obligation and the O2 does you the most good while you're still in the water.
Running some schedules in vplanner you'll see that there isn't a noticable difference in run time even between using a 20 ft stop as a last stop and a 10 ft stop.
Obviously in this case there isn't any inert gas in the inspired gas and the only difference is in ambient pressure.
For me it means no decompression on back gas especially if it's air. As far as I'm concerned it's a good idea to have a bottle of O2 around anyway especially fi you incuring a "mandatory decompression obligation and the O2 does you the most good while you're still in the water.
OP
As this thread goes on let me explain that this question, verbatum is from a advanced nitrox certification exam and really has a very simple answer, physiology aside. When you are comparing computers vs table usage there is a difference in your obligation to decompression diving.
GDI:
My short answer is "Yes"
AFAIC, for all practical purposes if you've calculated and followed your deco plan and you're on the correct gasses, as Mike noted, there is no difference between doing your "10' stop" at 10' or 15'.
If the wind picks up during the dive and the seas get a little nasty, I'd have no qualms about adding my 10' stop time to my 20' stop and simply hanging at 20' for the total duration. I also generally take it real slow coming up to the ladder from 20', after finishing with the hang.
pdoege
Contributor
The correct answer IMO is to dive your plan.
In any event, I have the last stop set to 20' in V-Planner. My thinking is that it avoids chop and whatnot at 10'. I'd rather spend another minute (or whatever) at 20'.
I also insert 2 minutes or so at 70' to make sure that I have plenty of time to shoot my bag, fowl it, re-shoot, grab my buddies bag, and then shoot that.
These changes seem to have little effect on the actual deco times, but I like having them in the deco schedule instead of winging it.
Peter
In any event, I have the last stop set to 20' in V-Planner. My thinking is that it avoids chop and whatnot at 10'. I'd rather spend another minute (or whatever) at 20'.
I also insert 2 minutes or so at 70' to make sure that I have plenty of time to shoot my bag, fowl it, re-shoot, grab my buddies bag, and then shoot that.
These changes seem to have little effect on the actual deco times, but I like having them in the deco schedule instead of winging it.
Peter
Similar threads
