Value of "Deco" gas on NDL dives?

**neilh** · May 10th, 2006, 10:33 AM

Not sure whether there is an easy answer to this, but here goes

Assuming several no deco dives over a number of days using 32% - is there any value in switching to a higher %o2 (e.g. 50%) for the ascent (at an appropriate depth of course)?

This came from a chat about getting some dives in with a stage/deco bottle just to get used to having one and then wondering whether there is any mileage in actually using it if its there...

Sterny · May 10th, 2006, 10:50 AM

Great question Neil - I'd be interested in people's thoughts about that too.

*JohnKendall* · May 10th, 2006, 10:54 AM

Quote: (Originally Posted by neilh)

Not sure whether there is an easy answer to this, but here goes

Assuming several no deco dives over a number of days using 32% - is there any value in switching to a higher %o2 (e.g. 50%) for the ascent (at an appropriate depth of course)?

This came from a chat about getting some dives in with a stage/deco bottle just to get used to having one and then wondering whether there is any mileage in actually using it if its there...

Unless the dives are really long, at the depth that you would switch to 50% you are basically just increasing your deco obligation. Using O2 would help clean up the deco, but at the increased risk and hassle of carrying an O2 bottle.

If you are doing NDL (or minimum Deco) dives, then a higher O2% gas won't be helping you, and you are taking additional risk carrying the bottle.

Look at it the other way around, why are you carrying the bottle? If it is because you want to do Tech1 and want the practice carrying it, then do that, Carry it, but don't switch. How are you going to switch to it? Who taught you the procedure for switching? How are you sure you are doing it Right?

HTH
J

*Hassan Adly* · May 10th, 2006, 12:04 PM

Hello,

I believe that the risks and inconvenience outweigh the benefits as far as carrying a deco stage is concerned. As long as you are staying within minimum deco and you are using 32% or 30/30, a second gas is a hassle to analyse, set up, carry, switch to, etc. If you are planning extended deco dives then it makes sense, as long as you have the right training.

As for simply practicing stage management, my advice would be to take a stage of the same contents as your backgas, preferably a 40cu. ft. cylinder. That way you can get accustomed to diving with it. If your buddy is properly trained he or she can give you some tips on practicing gas switches in shallow water with an emphasis on the buddy watching you do it.

*Clare Gledhill* · May 10th, 2006, 12:08 PM

Just a quick note though, in the UK we don't use 40s for Tech 1. A 7 or an 80 is fine.

jamesd · May 10th, 2006, 12:09 PM

Hi,

I am currently enjoying diving on just the double 12's, thinking about things I learnt in the DIRF and diving within the 32% range.
From my perspective I can't really see much/any benefit from carrying an additional tank at the moment. It is just another thing to buy, fill, service, carry onto/off the boat, clip onto yourself, carry around underwater for not really any advantage.

James

**neilh** · May 10th, 2006, 12:17 PM

Quote: (Originally Posted by JohnKendall)

If you are doing NDL (or minimum Deco) dives, then a higher O2% gas won't be helping you, and you are taking additional risk carrying the bottle.

That answers that then

Quote: (Originally Posted by JohnKendall)

Look at it the other way around, why are you carrying the bottle? If it is because you want to do Tech1 and want the practice carrying it, then do that, Carry it, but don't switch. How are you going to switch to it? Who taught you the procedure for switching? How are you sure you are doing it Right?

A fair point - I guess it comes down to the temptation to go that little bit further but, as you rightly point out, without appropriate training. I guess it's not unlike wanting to see what's round the next bend in a cave!

Thanks though John - curiosity satisfied and eagerness reigned in

graham_hk · May 10th, 2006, 02:18 PM

Quote: (Originally Posted by Gledders)

Just a quick note though, in the UK we don't use 40s for Tech 1. A 7 or an 80 is fine.

Al40s seem to be the bottle of choice in other locales - why is UK different? Is it an availability issue?

*JohnKendall* · May 10th, 2006, 02:43 PM

Quote: (Originally Posted by graham_hk)

Al40s seem to be the bottle of choice in other locales - why is UK different? Is it an availability issue?

Gas consumption would be my guess. Certainly I find I can't do any more than 30mins of deco on a 7L, so prefer an AL80 for 50% (If only using 1 deco gas)

Conditions in the UK are not all that great for keeping gas consumption low, especially when doing Tech1 training dives.

J

mstroeck · May 10th, 2006, 05:13 PM

Quote: (Originally Posted by JohnKendall)

If it is because you want to do Tech1 and want the practice carrying it, then do that, Carry it, but don't switch. How are you going to switch to it? Who taught you the procedure for switching? How are you sure you are doing it Right?

I'm all for DIR and getting education, and whatnot, but do you seriously believe an average adult person needs a course to in order to be able to safely switch to 02 at 6 meters?

May 10th, 2006, 10:33 AM	#1 (permalink)
neilh(Offline) Haemoglobin on the bus... Join Date: Nov 2005 Location: Barnsley, UK Posts: 1,900	Value of "Deco" gas on NDL dives? Not sure whether there is an easy answer to this, but here goes Assuming several no deco dives over a number of days using 32% - is there any value in switching to a higher %o2 (e.g. 50%) for the ascent (at an appropriate depth of course)? This came from a chat about getting some dives in with a stage/deco bottle just to get used to having one and then wondering whether there is any mileage in actually using it if its there...

May 10th, 2006, 10:50 AM	#2 (permalink)
Sterny(Offline) New Member Join Date: Nov 2005 Location: The limpid tropical lagoons of Ealing, West London Posts: 550	Great question Neil - I'd be interested in people's thoughts about that too. __________________ "I thought I had a great idea today, but it never really took off. In fact, it didn't even get on the runway. I guess you could say it exploded in the hangar." - Bill Watterson, Calvin and Hobbes

May 10th, 2006, 10:54 AM	#3 (permalink)
JohnKendall(Offline) GUE Instructor/DIRX Moderator Join Date: Nov 2005 Location: Cambridge, UK Posts: 1,097	Quote: (Originally Posted by neilh) Not sure whether there is an easy answer to this, but here goes Assuming several no deco dives over a number of days using 32% - is there any value in switching to a higher %o2 (e.g. 50%) for the ascent (at an appropriate depth of course)? This came from a chat about getting some dives in with a stage/deco bottle just to get used to having one and then wondering whether there is any mileage in actually using it if its there... Unless the dives are really long, at the depth that you would switch to 50% you are basically just increasing your deco obligation. Using O2 would help clean up the deco, but at the increased risk and hassle of carrying an O2 bottle. If you are doing NDL (or minimum Deco) dives, then a higher O2% gas won't be helping you, and you are taking additional risk carrying the bottle. Look at it the other way around, why are you carrying the bottle? If it is because you want to do Tech1 and want the practice carrying it, then do that, Carry it, but don't switch. How are you going to switch to it? Who taught you the procedure for switching? How are you sure you are doing it Right? HTH J __________________ John Kendall http://www.guetraining.com/ GUE Instruction, Santi and Halcyon Equipment NEW - Online Santi Shop

May 10th, 2006, 12:04 PM	#4 (permalink)
Hassan Adly(Offline) GUE Instructor Join Date: Feb 2006 Location: Red Sea Posts: 286	Hello, I believe that the risks and inconvenience outweigh the benefits as far as carrying a deco stage is concerned. As long as you are staying within minimum deco and you are using 32% or 30/30, a second gas is a hassle to analyse, set up, carry, switch to, etc. If you are planning extended deco dives then it makes sense, as long as you have the right training. As for simply practicing stage management, my advice would be to take a stage of the same contents as your backgas, preferably a 40cu. ft. cylinder. That way you can get accustomed to diving with it. If your buddy is properly trained he or she can give you some tips on practicing gas switches in shallow water with an emphasis on the buddy watching you do it. __________________ Hassan Adly Red Sea Discovery "Today I will finally see the sea again, which will smell of salt, wind, sand - and the cold of winter. Finally I will not only travel on it but dive in it, again I will become water, a bird - and I will remember the feeling of gliding above the abyss" Elena Sundukova, tragically lost at sea, January 2007

May 10th, 2006, 12:08 PM	#5 (permalink)
Clare Gledhill (Online) GUE Instructor Site Admin Join Date: Nov 2005 Location: UK Posts: 1,540	Just a quick note though, in the UK we don't use 40s for Tech 1. A 7 or an 80 is fine. __________________ Clare . "Keep away from people who try to belittle your ambitions....Small people always do that, but the really great make you feel that you too can become great." Interested in DIR dive training? Always happy to chat/answer questions so get in touch via PM or visit www.dirdiver.co.uk

May 10th, 2006, 12:09 PM	#6 (permalink)
jamesd(Offline) New Member Join Date: Jan 2006 Location: London Posts: 54	Hi, I am currently enjoying diving on just the double 12's, thinking about things I learnt in the DIRF and diving within the 32% range. From my perspective I can't really see much/any benefit from carrying an additional tank at the moment. It is just another thing to buy, fill, service, carry onto/off the boat, clip onto yourself, carry around underwater for not really any advantage. James

May 10th, 2006, 12:17 PM	#7 (permalink)
neilh(Offline) Haemoglobin on the bus... Join Date: Nov 2005 Location: Barnsley, UK Posts: 1,900	Quote: (Originally Posted by JohnKendall) If you are doing NDL (or minimum Deco) dives, then a higher O2% gas won't be helping you, and you are taking additional risk carrying the bottle. That answers that then Quote: (Originally Posted by JohnKendall) Look at it the other way around, why are you carrying the bottle? If it is because you want to do Tech1 and want the practice carrying it, then do that, Carry it, but don't switch. How are you going to switch to it? Who taught you the procedure for switching? How are you sure you are doing it Right? A fair point - I guess it comes down to the temptation to go that little bit further but, as you rightly point out, without appropriate training. I guess it's not unlike wanting to see what's round the next bend in a cave! Thanks though John - curiosity satisfied and eagerness reigned in

May 10th, 2006, 02:18 PM	#8 (permalink)
graham_hk(Offline) Pinoy ako pinoy Join Date: Nov 2005 Location: here, there and everywhere Posts: 779	Quote: (Originally Posted by Gledders) Just a quick note though, in the UK we don't use 40s for Tech 1. A 7 or an 80 is fine. Al40s seem to be the bottle of choice in other locales - why is UK different? Is it an availability issue?

May 10th, 2006, 02:43 PM	#9 (permalink)
JohnKendall(Offline) GUE Instructor/DIRX Moderator Join Date: Nov 2005 Location: Cambridge, UK Posts: 1,097	Quote: (Originally Posted by graham_hk) Al40s seem to be the bottle of choice in other locales - why is UK different? Is it an availability issue? Gas consumption would be my guess. Certainly I find I can't do any more than 30mins of deco on a 7L, so prefer an AL80 for 50% (If only using 1 deco gas) Conditions in the UK are not all that great for keeping gas consumption low, especially when doing Tech1 training dives. J __________________ John Kendall http://www.guetraining.com/ GUE Instruction, Santi and Halcyon Equipment NEW - Online Santi Shop

May 10th, 2006, 05:13 PM	#10 (permalink)
mstroeck(Offline) New Member Join Date: Nov 2005 Location: Vienna, Austria Posts: 156	Quote: (Originally Posted by JohnKendall) If it is because you want to do Tech1 and want the practice carrying it, then do that, Carry it, but don't switch. How are you going to switch to it? Who taught you the procedure for switching? How are you sure you are doing it Right? I'm all for DIR and getting education, and whatnot, but do you seriously believe an average adult person needs a course to in order to be able to safely switch to 02 at 6 meters?