Hypothetical question about decompression

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

Joining is quick and easy. Log in or Register now!

jaycanwk

Contributor
Messages
194
Reaction score
48
Location
Kitchener Ontario Canada
# of dives
50 - 99
This is a hypothetical question, as I've been doing some reading on decompression theory lately.

Lets say you do a dive to 150ft that reqired at total accent time of 60 min. where you would do a staged acent stopping at the reqired stops for the reqired time.

Would this be, in theory, and assuming it were possible to even physically do this, the same as making a direct controled acent of 2.5ft/min without stopping from 150ft???

In other words is a direct acent totaling 60min the same as a staged acent totalling 60min from the same depth?

I hope that makes sense.
 
As a new diver, I've been reading everything I encounter about different aspects of diving, including decompression theory, as general background knowledge, even though I never intend to do decompression diving.

SO TAKE EVERYTHING I SAY WITH SOME SALT!

If you look at decompression tables, it looks to me as though the deeper stops are generally shorter and farther apart than the shallower stops. The shallower stops can be quite long.

This suggest to me that the answer to your question is probably a very big NO NO NO!!!

Decompression theory and calculations are very complex, and simple assumptions that do not take conditions and physiology into account are probably ill advised, and could possibly be fatal.

You'll probably get more educated replies from folks who know what they're talking about, but I'll bet dollars to doughnuts that they'll agree that the bottom line answer to your question is that a constant ascent rate is NOT the same as following the decompression table or computer algorithm.
 
Here is my standard deco plan to 150 ft, with contingencies.

I have used this one many times, and it works.

Deco plans are meant to be followed. Not abbreviated.

Now, what was it that you were asking about??


150 FT 20 MINS TMX 25 / 35 +3 ALL EVENTS / NO FAILURES

V-Planner 3.43 by R. Hemingway, VPM code by Erik C. Baker.
Decompression model: VPM-B

DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (3) on Trimix 25.0/35.0, 50ft/min descent.
Level 150ft 17:00 (20) on Trimix 25.0/35.0, 1.38 ppO2, 60ft ead, 86ft end
Asc to 70ft (22) on Trimix 25.0/35.0, -30ft/min ascent.
Asc to 60ft (23) on Nitrox 50.0, -30ft/min ascent.
Stop at 60ft 1:00 (24) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 1:00 (25) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 1:00 (26) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 2:00 (28) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 1:00 (29) on Oxygen, 1.60 ppO2, 0ft ead
Stop at 15ft 7:00 (36) on Oxygen, 1.45 ppO2, 0ft ead
Asc to sfc. (36) on Oxygen, -30ft/min ascent.

Off gassing starts at 97.1ft

OTU's this dive: 54
CNS Total: 22.4%

86.6 cu ft Trimix 25.0/35.0
7.5 cu ft Nitrox 50.0
5.9 cu ft Oxygen
100 cu ft TOTAL

DIVE PLAN #2
Surface interval = 0 day 2 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (3) on Trimix 25.0/35.0, 50ft/min descent.
Level 150ft 17:00 (20) on Trimix 25.0/35.0, 1.38 ppO2, 60ft ead, 86ft end
Asc to 70ft (22) on Trimix 25.0/35.0, -30ft/min ascent.
Asc to 60ft (23) on Nitrox 50.0, -30ft/min ascent.
Stop at 60ft 1:00 (24) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 1:00 (25) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 1:00 (26) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 2:00 (28) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 2:00 (30) on Oxygen, 1.60 ppO2, 0ft ead
Stop at 15ft 8:00 (38) on Oxygen, 1.45 ppO2, 0ft ead
Asc to sfc. (38) on Oxygen, -30ft/min ascent.

Off gassing starts at 97.1ft

OTU's this dive: 58
CNS Total: 39.4%

86.6 cu ft Trimix 25.0/35.0
7.5 cu ft Nitrox 50.0
7.5 cu ft Oxygen
101.5 cu ft TOTAL

DIVE PLAN COMPLETE


150 FT 20 MINS TMX 25 / 35 +3 / FAILURE OF EAN 50 BOTTLE

DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (3) on Trimix 25.0/35.0, 50ft/min descent.
Level 150ft 17:00 (20) on Trimix 25.0/35.0, 1.38 ppO2, 60ft ead, 86ft end
Asc to 70ft (22) on Trimix 25.0/35.0, -30ft/min ascent.
Stop at 70ft 0:20 (23) on Trimix 25.0/35.0, 0.78 ppO2, 19ft ead, 34ft end
Stop at 60ft 1:00 (24) on Trimix 25.0/35.0, 0.70 ppO2, 14ft ead, 27ft end
Stop at 50ft 1:00 (25) on Trimix 25.0/35.0, 0.63 ppO2, 9ft ead, 21ft end
Stop at 40ft 3:00 (28) on Trimix 25.0/35.0, 0.55 ppO2, 4ft ead, 14ft end
Stop at 30ft 4:00 (32) on Trimix 25.0/35.0, 0.48 ppO2, 0ft ead, 8ft end
Stop at 20ft 2:00 (34) on Oxygen, 1.60 ppO2, 0ft ead
Stop at 15ft 7:00 (41) on Oxygen, 1.45 ppO2, 0ft ead
Asc to sfc. (41) on Oxygen, -30ft/min ascent.

Off gassing starts at 97.1ft

OTU's this dive: 50
CNS Total: 22.8%

97.6 cu ft Trimix 25.0/35.0
6.7 cu ft Oxygen
104.3 cu ft TOTAL

DIVE PLAN #2
Surface interval = 0 day 2 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (3) on Trimix 25.0/35.0, 50ft/min descent.
Level 150ft 17:00 (20) on Trimix 25.0/35.0, 1.38 ppO2, 60ft ead, 86ft end
Asc to 70ft (22) on Trimix 25.0/35.0, -30ft/min ascent.
Asc to 60ft (23) on Nitrox 50.0, -30ft/min ascent.
Stop at 60ft 1:00 (24) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 1:00 (25) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 1:00 (26) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 2:00 (28) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 1:00 (29) on Oxygen, 1.60 ppO2, 0ft ead
Stop at 15ft 8:00 (37) on Oxygen, 1.45 ppO2, 0ft ead
Asc to sfc. (37) on Oxygen, -30ft/min ascent.

Off gassing starts at 97.1ft

OTU's this dive: 56
CNS Total: 37.5%

86.6 cu ft Trimix 25.0/35.0
7.5 cu ft Nitrox 50.0
6.7 cu ft Oxygen
100.7 cu ft TOTAL

DIVE PLAN COMPLETE


150 FT 20 MINS TMX 25 / 35 +3 / FAILURE OF 100% O2 BOTTLE

DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (3) on Trimix 25.0/35.0, 50ft/min descent.
Level 150ft 17:00 (20) on Trimix 25.0/35.0, 1.38 ppO2, 60ft ead, 86ft end
Asc to 70ft (22) on Trimix 25.0/35.0, -30ft/min ascent.
Stop at 70ft 0:20 (23) on Nitrox 50.0, 1.56 ppO2, 32ft ead
Stop at 60ft 1:00 (24) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 1:00 (25) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 1:00 (26) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 2:00 (28) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 2:00 (30) on Nitrox 50.0, 0.80 ppO2, 1ft ead
Stop at 15ft 10:00 (40) on Nitrox 50.0, 0.73 ppO2, 0ft ead
Asc to sfc. (40) on Nitrox 50.0, -30ft/min ascent.

Off gassing starts at 97.1ft

OTU's this dive: 47
CNS Total: 18.0%

86.6 cu ft Trimix 25.0/35.0
15.8 cu ft Nitrox 50.0
102.4 cu ft TOTAL

DIVE PLAN #2
Surface interval = 0 day 2 hr 0 min.
Elevation = 0ft
Conservatism = + 3

Dec to 150ft (3) on Trimix 25.0/35.0, 50ft/min descent.
Level 150ft 17:00 (20) on Trimix 25.0/35.0, 1.38 ppO2, 60ft ead, 86ft end
Asc to 70ft (22) on Trimix 25.0/35.0, -30ft/min ascent.
Asc to 60ft (23) on Nitrox 50.0, -30ft/min ascent.
Stop at 60ft 1:00 (24) on Nitrox 50.0, 1.41 ppO2, 26ft ead
Stop at 50ft 1:00 (25) on Nitrox 50.0, 1.26 ppO2, 20ft ead
Stop at 40ft 1:00 (26) on Nitrox 50.0, 1.10 ppO2, 13ft ead
Stop at 30ft 2:00 (28) on Nitrox 50.0, 0.95 ppO2, 7ft ead
Stop at 20ft 1:00 (29) on Oxygen, 1.60 ppO2, 0ft ead
Stop at 15ft 9:00 (38) on Oxygen, 1.45 ppO2, 0ft ead
Asc to sfc. (38) on Oxygen, -30ft/min ascent.

Off gassing starts at 97.1ft

OTU's this dive: 57
CNS Total: 35.1%

86.6 cu ft Trimix 25.0/35.0
7.5 cu ft Nitrox 50.0
7.4 cu ft Oxygen
101.5 cu ft TOTAL

DIVE PLAN COMPLETE
 
Last edited:
This is a hypothetical question, as I've been doing some reading on decompression theory lately.

Lets say you do a dive to 150ft that reqired at total accent time of 60 min. where you would do a staged acent stopping at the reqired stops for the reqired time.

Would this be, in theory, and assuming it were possible to even physically do this, the same as making a direct controled acent of 2.5ft/min without stopping from 150ft???

In other words is a direct acent totaling 60min the same as a staged acent totalling 60min from the same depth?

I hope that makes sense.

No, it would not. I could write a long explanation about why ... but I only have a few minutes before class, so I'll leave that for someone else to explain.

But the simple answer to your question is no.

Nereas, I haven't a clue what you were attempting to answer by pasting a bunch of V-planner profiles ... I suspect you don't either.

... Bob (Grateful Diver)
 
...

Nereas, I haven't a clue what you were attempting to answer by pasting a bunch of V-planner profiles ... I suspect you don't either.

... Bob (Grateful Diver)

Well the poor guy has never seen a deco plan, and you are too much in a hurry to show him one, whereas I happen to have one ready to go, so I have done the honors.

Although I suspect that you don't know either.:rofl3:
 
Thakyou for the responses so far.

So i guess the quick answer is no?

Is it because there is a certain depth where u are still on gassing faster than off gassing? cause i did notice the part in nereas's Vplanner profile where it says ""offgassing starts at 97.1ft"" for that particular profile.
 
Conventional decompression theory holds that different groups of tissue absorb and release gas at different rates. The release of this gas must be controlled within a certain limit often called M-value which is the maximum pressure the tissue (compartment) can hold above ambient pressure before the risk of producing bubbles become a problem. For a given dive compartments that absorb gas faster will be closer to saturation than slower compartments and it is for these compartments that we start making our first (deeper) stops. As those tissue compartments release gas to fall to a lower gradient we are able to move closer to the surface but now the slower compartments start to reach their M-value and we have to stop until they have released enough gas to continue upward. As we get closer to the surface the tissues compartment that prevents our ascent (controlling tissue) is the slower compartment and therefore we have to wait longer for them to offgas to an acceptable level. According to Buhlmann ZHL-16A for nitrogen decompression (air, not helium) the tissue half times range from 4 minutes for the fastest tissue to 635 minutes for the slowest tissue.
Hope that makes sense.
 
Thakyou for the responses so far.

So i guess the quick answer is no?

Is it because there is a certain depth where u are still on gassing faster than off gassing? cause i did notice the part in nereas's Vplanner profile where it says ""offgassing starts at 97.1ft"" for that particular profile.

The answer is "no thou shalt never violate a deco plan."

The reason why it because it could forever ruin your woody.

Or even put you into a wheelchair with an incontinence bag.

That is why. Those are findings of fact, not just theory.

I haven't a clue why NWGREATFUL's mind does not comprehend obvious things. But that could happen too, as a matter of fact.
 
Conventional decompression theory holds that different groups of tissue absorb and release gas at different rates. The release of this gas must be controlled within a certain limit often called M-value which is the maximum pressure the tissue (compartment) can hold above ambient pressure before the risk of producing bubbles become a problem. For a given dive compartments that absorb gas faster will be closer to saturation than slower compartments and it is for these compartments that we start making our first (deeper) stops. As those tissue compartments release gas to fall to a lower gradient we are able to move closer to the surface but now the slower compartments start to reach their M-value and we have to stop until they have released enough gas to continue upward. As we get closer to the surface the tissues compartment that prevents our ascent (controlling tissue) is the slower compartment and therefore we have to wait longer for them to offgas to an acceptable level. According to Buhlmann ZHL-16A for nitrogen decompression (air, not helium) the tissue half times range from 4 minutes for the fastest tissue to 635 minutes for the slowest tissue.
Hope that makes sense.


Yes, that makes perfect sense. Thankyou.
 
I don't know what you are reading but it should be "Deco For Divers" by Mark Powell.

You can get a brief overview of the "Suunto Reduced Gradient Bubble Model" (as implemented in their computers) at http://www.dive-tech.co.uk/resources/suunto-rgbm.pdf

There are other documents you can find via Google. Search for 'decompression theory'. The problem with the Internet results is that anyone can write anything. It may, or may not, be correct.

Of course, you could do it the easy way and take some TDI courses.

I know almost nothing about deco. But I darn sure wouldn't take a schedule posted to an Internet forum as a plan that would protect my life. By nature, I don't trust anybody. If I don't plan the dive, I won't dive the plan. But then, I am just a recreational diver, uninterested in the vagaries of deco theory.

Richard
 
https://www.shearwater.com/products/perdix-ai/

Back
Top Bottom