Think piece: Nitrox vs. Rebreather dive planning

warjarrett · 16th October 2007, 21:47

A Nitrox diver chooses 32% O2 to dive at 100 ft (30m). His buddy, a rebreather diver, chooses a set point of 1.3 for the same dive. How will the two divers' plans differ, and will there be a difference in their time limits? Will their recommended surface interval and 2nd dive time (to the same depth) differ?

**almity1** · 17th October 2007, 00:37

Because I use a Non Integrated Computer...

Using your scenario, my computer (not a VR3) would be set to 32% (Setpoint/ATA that is 1.3/4 = 0.325).

So I would have a similar profile but my Oxygen Exposure will be different and have to be taken into the account with the Rebreather diving having the Constant P02 and not varying as per the Nitrox Diver.

Using a Integrated Computer such as VR3 where you can set the setpoint there may be a different scenario. Hoping that others will comment on this

Drmike · 17th October 2007, 03:52

Quote: (Originally Posted by warjarrett)

A Nitrox diver chooses 32% O2 to dive at 100 ft (30m). His buddy, a rebreather diver, chooses a set point of 1.3 for the same dive. How will the two divers' plans differ, and will there be a difference in their time limits? Will their recommended surface interval and 2nd dive time (to the same depth) differ?

Dead man walking??

Do a course.

You cant/shouldnt learn to dive rebreathers on the internet.

Russ · 17th October 2007, 05:05

Depending on the bottom time..

Generally speaking for that dive the CCR will give you "perfect" nitrox so the
CCR will have more time til deco or less deco on the first and second dives plus you could probably do the same dive twice and not have to change anything between dives

Russ

If you want more info look for differences in breathing a changing PO2 versus breathing a constant PO2

warjarrett · 17th October 2007, 05:30

Well, I am thinking that both divers are spending their complete bottom time breathing EXACTLY the same gas. And, therefore if one where to use tables to plan the dive (not just brainlessly rely on whatever the computer tells you), both divers would come up with EXACTLY the same dive profiles -- before they even entered the water.

Abbo · 17th October 2007, 05:34

The PN2 is 2.72 in the first case and 2.7 in the second, but the difference is not significant given that decompression models are very imprecise to put it mildly. The difference comes as you surface: at 10m, the OC nitrox diver has a PN2 of 1.36, where the rebreather diver has a PN2 of 0.7. For all depths less than maximum depth, the rebreather diver has a lower PN2, and is therefore taking on less nitrogen on the decent and offgassing more on the ascent. This makes little diifference on a periscope-depth dive like this, but it makes a huge difference on a deeper dive: if you ascend at 9m/min, as you should, it will take you 11.1 minutes to ascend from 100m, and though you can descend slightly faster than 9m/min, the descent time has a quite significant effect on the decompression time also. Obviously you would have to be nuttier than squirrel poop to dive to 100m on air, but the principals are the same.

**Steve** · 17th October 2007, 06:19

Quote: (Originally Posted by warjarrett)

Why is DrMike so ready to abuse, condemn and put down.. that is, say that I am going to die, because I want to hear people's answers to questions that we should all know? And, why cant he answer the questions with the same expenditure of enthusiasm? Is it because he is better at condemning than explaining? Or maybe his understanding of human stupidity exceeds his understanding of dive theory. Well, my answer is that both divers are spending their complete bottom time breathing EXACTLY the same gas. And, therefore if one where to use tables to plan the dive (not just brainlessly rely on whatever the computer tells you), both divers would come up with EXACTLY the same dive profiles -- before they even entered the water.

He is cranky because all the questions you pose are really really really fundamental topics that no one who is qualified should be asking due to the information being really really really well understood by anyone who has been trained. I'm not just referring to this thread. You scare the crap out of me mate. Go and do another course with a different instructor......please

decoweenie · 17th October 2007, 07:08

Quote: (Originally Posted by Steve)

Go and do another course with a different instructor......please

It is not always the instructor's fault.

Reading some of the questions here, IMHO some people shouldn't get anywhere near a CCR, compressor or booster.

jhaaja · 17th October 2007, 07:39

Quote: (Originally Posted by warjarrett)

Why is DrMike so ready to abuse, condemn and put down.. that is, say that I am going to die, because I want to hear people's answers to questions that we should all know? And, why cant he answer the questions with the same expenditure of enthusiasm? Is it because he is better at condemning than explaining? Or maybe his understanding of human stupidity exceeds his understanding of dive theory. Well, my answer is that both divers are spending their complete bottom time breathing EXACTLY the same gas. And, therefore if one where to use tables to plan the dive (not just brainlessly rely on whatever the computer tells you), both divers would come up with EXACTLY the same dive profiles -- before they even entered the water.

How will the OC nitrox divers ppO2 behave during the accent?

warjarrett · 17th October 2007, 08:18

These questions were tests, mostly to confirm some subtle related details that my theory study has made me think about. I asked them from the basic perspective to see if the more advanced aspects of the questions would surface. But, I must say, I was surprised that the issue of dive planning was not disscussed. Not encouaging dive planning is one kind of failure, in this test question. Other answers show that some of you care more about proving how conceited you are than about helping new divers undertstand. This is a bigger failure. I believe some of you that not understanding basics causes deaths. Not thinking is even more dangerous. Asking questions and being helpful saves lives. But, condemning people for asking questions that YOU think are stupid probably is the most dangerous of all.

16th October 2007, 21:47	#1 (permalink)
warjarrett New Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: May 2007 Location: Los Angeles Posts: 48	Think piece: Nitrox vs. Rebreather dive planning A Nitrox diver chooses 32% O2 to dive at 100 ft (30m). His buddy, a rebreather diver, chooses a set point of 1.3 for the same dive. How will the two divers' plans differ, and will there be a difference in their time limits? Will their recommended surface interval and 2nd dive time (to the same depth) differ?
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17th October 2007, 00:37	#2 (permalink)
almity1 No Viz is BAD Viz Current Rebreather/s: Megalodon Other Rebreather/s: Evolution Prism Topaz Sport Kiss Optima Join Date: Aug 2006 Location: Sydney, Australia Posts: 176	Re: Think piece: Nitrox vs. Rebreather dive planning Because I use a Non Integrated Computer... Using your scenario, my computer (not a VR3) would be set to 32% (Setpoint/ATA that is 1.3/4 = 0.325). So I would have a similar profile but my Oxygen Exposure will be different and have to be taken into the account with the Rebreather diving having the Constant P02 and not varying as per the Nitrox Diver. Using a Integrated Computer such as VR3 where you can set the setpoint there may be a different scenario. Hoping that others will comment on this __________________ Cheers almity1 - http://www.almity1.com
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17th October 2007, 03:52	#3 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,113	Re: Think piece: Nitrox vs. Rebreather dive planning Quote: (Originally Posted by warjarrett) A Nitrox diver chooses 32% O2 to dive at 100 ft (30m). His buddy, a rebreather diver, chooses a set point of 1.3 for the same dive. How will the two divers' plans differ, and will there be a difference in their time limits? Will their recommended surface interval and 2nd dive time (to the same depth) differ? Dead man walking?? Do a course. You cant/shouldnt learn to dive rebreathers on the internet. __________________ Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you
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17th October 2007, 05:05	#4 (permalink)
Russ New Member Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Jul 2006 Posts: 88	Re: Think piece: Nitrox vs. Rebreather dive planning Depending on the bottom time.. Generally speaking for that dive the CCR will give you "perfect" nitrox so the CCR will have more time til deco or less deco on the first and second dives plus you could probably do the same dive twice and not have to change anything between dives Russ If you want more info look for differences in breathing a changing PO2 versus breathing a constant PO2 Last edited by Russ : 17th October 2007 at 05:07.
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17th October 2007, 05:30	#5 (permalink)
warjarrett New Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: May 2007 Location: Los Angeles Posts: 48	Re: Think piece: Nitrox vs. Rebreather dive planning Well, I am thinking that both divers are spending their complete bottom time breathing EXACTLY the same gas. And, therefore if one where to use tables to plan the dive (not just brainlessly rely on whatever the computer tells you), both divers would come up with EXACTLY the same dive profiles -- before they even entered the water. Last edited by warjarrett : 17th October 2007 at 18:43.
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17th October 2007, 05:34	#6 (permalink)
Abbo Going down on Meg Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 380	Re: Think piece: Nitrox vs. Rebreather dive planning The PN2 is 2.72 in the first case and 2.7 in the second, but the difference is not significant given that decompression models are very imprecise to put it mildly. The difference comes as you surface: at 10m, the OC nitrox diver has a PN2 of 1.36, where the rebreather diver has a PN2 of 0.7. For all depths less than maximum depth, the rebreather diver has a lower PN2, and is therefore taking on less nitrogen on the decent and offgassing more on the ascent. This makes little diifference on a periscope-depth dive like this, but it makes a huge difference on a deeper dive: if you ascend at 9m/min, as you should, it will take you 11.1 minutes to ascend from 100m, and though you can descend slightly faster than 9m/min, the descent time has a quite significant effect on the decompression time also. Obviously you would have to be nuttier than squirrel poop to dive to 100m on air, but the principals are the same.
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17th October 2007, 06:19	#7 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,050	Re: Think piece: Nitrox vs. Rebreather dive planning Quote: (Originally Posted by warjarrett) Why is DrMike so ready to abuse, condemn and put down.. that is, say that I am going to die, because I want to hear people's answers to questions that we should all know? And, why cant he answer the questions with the same expenditure of enthusiasm? Is it because he is better at condemning than explaining? Or maybe his understanding of human stupidity exceeds his understanding of dive theory. Well, my answer is that both divers are spending their complete bottom time breathing EXACTLY the same gas. And, therefore if one where to use tables to plan the dive (not just brainlessly rely on whatever the computer tells you), both divers would come up with EXACTLY the same dive profiles -- before they even entered the water. He is cranky because all the questions you pose are really really really fundamental topics that no one who is qualified should be asking due to the information being really really really well understood by anyone who has been trained. I'm not just referring to this thread. You scare the crap out of me mate. Go and do another course with a different instructor......please __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
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17th October 2007, 07:08	#8 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,510	Re: Think piece: Nitrox vs. Rebreather dive planning Quote: (Originally Posted by Steve) Go and do another course with a different instructor......please It is not always the instructor's fault. Reading some of the questions here, IMHO some people shouldn't get anywhere near a CCR, compressor or booster.
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17th October 2007, 07:39	#9 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 867	Re: Think piece: Nitrox vs. Rebreather dive planning Quote: (Originally Posted by warjarrett) Why is DrMike so ready to abuse, condemn and put down.. that is, say that I am going to die, because I want to hear people's answers to questions that we should all know? And, why cant he answer the questions with the same expenditure of enthusiasm? Is it because he is better at condemning than explaining? Or maybe his understanding of human stupidity exceeds his understanding of dive theory. Well, my answer is that both divers are spending their complete bottom time breathing EXACTLY the same gas. And, therefore if one where to use tables to plan the dive (not just brainlessly rely on whatever the computer tells you), both divers would come up with EXACTLY the same dive profiles -- before they even entered the water. How will the OC nitrox divers ppO2 behave during the accent?
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17th October 2007, 08:18	#10 (permalink)
warjarrett New Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: May 2007 Location: Los Angeles Posts: 48	Re: Think piece: Nitrox vs. Rebreather dive planning These questions were tests, mostly to confirm some subtle related details that my theory study has made me think about. I asked them from the basic perspective to see if the more advanced aspects of the questions would surface. But, I must say, I was surprised that the issue of dive planning was not disscussed. Not encouaging dive planning is one kind of failure, in this test question. Other answers show that some of you care more about proving how conceited you are than about helping new divers undertstand. This is a bigger failure. I believe some of you that not understanding basics causes deaths. Not thinking is even more dangerous. Asking questions and being helpful saves lives. But, condemning people for asking questions that YOU think are stupid probably is the most dangerous of all. Last edited by warjarrett : 17th October 2007 at 18:51.
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