EKPP gases

Divingniknaks · October 31st, 2006, 03:55 PM

Having had a wander round the EKPP site the other day while downloading the video, I noticed something which sparked my curiosity.

It makes mention a few times of the 21M switch to 50/25 Trimix.

Just wondered what the more experienced amongst you thought to that as a "deco" gas v the "normal" 50%.

Accepting it's dearer of course, what advantages / disadvantages does it have to the deco ?

Question based on total ignorance as usual, so be gentle

Cheers

GLOC · October 31st, 2006, 04:06 PM

Have a look on the Ocean Discovery site and there is plenty of discussion on this, including using 50/50 as a deco gas.

The 2 bits I remember are that it provides a cleaner deco as there is an even bigger gas gradient and the bottle rides better.

I am sure someone with far more experience will be along to explain more...

Ahmed Adly, Marlin Inn DC · October 31st, 2006, 04:46 PM

50/25 rides well. That is the main reason it is used.

But there is some suspicion about the deco thingy too.

Ahmed

Gareth Burrows · October 31st, 2006, 04:51 PM

Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC)

50/25 rides well. That is the main reason it is used.

But there is some suspicion about the deco thingy too.

Ahmed

that's the most succinct and accurate expression of the DIR ethos I've ever seen.

:D

***Bob Cooper*** · October 31st, 2006, 05:07 PM

Quote: (Originally Posted by Divingniknaks)

Just wondered what the more experienced amongst you thought to that as a "deco" gas v the "normal" 50%.

The helium make the deco bottles closer to neutral when full.

There are also advantages to using some helium in the deco mix.

Janos · October 31st, 2006, 06:54 PM

I looked at this for a while. There's a fair bit over on The Deco Stop. And there's a thread I started on RBW.

My conclusion is that many people find 50/25 or 50/50 leaves them feeling better following a dive. However all the cases I saw where two (or more) stage dives where they used O2 at the final stage. The point here is that pure O2 is an He free gas; and He being "quick" gets out the system quicker.

Have a look at that Richard Pyle article (the one where he advocates deep stops 20m above the bottom, not 80%). Later on he talks about the relatively off gassing of different inerts and it all makes sense.

I decided against putting He in my shallow bottle (to make it ride better) as I wouldn't be finishing deco on O2 and I was worried about residual He.

Janos

*Hassan Adly* · October 31st, 2006, 07:25 PM

Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC)

50/25 rides well. That is the main reason it is used.

Hang on, before making sweeping statements like that let's see what the people who actually use it think...

Quote:

But there is some suspicion about the deco thingy too

There are quite clear reasons for using 50/25 or 50/50 as compared to 50% nitrox, and having a neutrally buoyant cylinder isn't the main reason.

Simply put, when you put helium in the 21m cylinder, you are reducing the nitrogen component and hence increasing the nitrogen gradient. This leads to more efficient offgassing of nitrogen as compared to 50% nitrox. This explains why people "feel" better after using 50/25 or 50/50.

Using helium in the 21m cylinder also means that we decrease the helium gradient and offgas helium more slowly, which is something that has to be accounted for in the deco profile - which is why you would normally see this gas used in conjunction with oxygen, where the "fast helium" effect comes into play.

50% nitrox is for when you want to get the helium out.

50/25 or 50/50 is for when you want to get the nitrogen out!

jluttichau · October 31st, 2006, 08:38 PM

Quote: (Originally Posted by Garf)

that's the most succinct and accurate expression of the DIR ethos I've ever seen.

:D

Why DIR: It rides well and theres something about the deco thingy too..

Cheers

GLOC · October 31st, 2006, 08:48 PM

Quote:

(Originally Posted by Ahmed Adly, Marlin Inn DC)

50/25 rides well. That is the main reason it is used.

Quote: (Originally Posted by Hassan Adly)

Hang on, before making sweeping statements like that let's see what the people who actually use it think...

You 2 sound like Garf and I!

lizardland · October 31st, 2006, 11:16 PM

It's advantageous in long decos to have a bit of helium, it's increasing the nitrogen gradient as stated, it's easier to breathe on long stops and (for whatever physiological reason) I think it makes you feel better. With a long bottom time on trimix then a switch to straight nitrox isn't a particularly good idea either.

On normalish deco dives I don't think there is much advantage, maybe even counter-productive. You will need to offgas the helium at some point, on a short deco then this may increase your deco time.

I generally breathe helium in my mix all the way up (one benefit of diving a rebreather

) but I always make sure I do full flushes at 6m so that I'm on pure O2 for the final stop.

October 31st, 2006, 03:55 PM	#1 (permalink)
Divingniknaks(Offline) Resident purveyor of shiney kit.... Join Date: Nov 2005 Location: Midlands UK Posts: 1,038	EKPP gases Having had a wander round the EKPP site the other day while downloading the video, I noticed something which sparked my curiosity. It makes mention a few times of the 21M switch to 50/25 Trimix. Just wondered what the more experienced amongst you thought to that as a "deco" gas v the "normal" 50%. Accepting it's dearer of course, what advantages / disadvantages does it have to the deco ? Question based on total ignorance as usual, so be gentle Cheers __________________ Phill ----------------------------- Salvo Lights, DirZone Gear , Frog Wings Dive ? http://www.divingniknaks.com

October 31st, 2006, 04:06 PM	#2 (permalink)
GLOC (Online) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,963	Have a look on the Ocean Discovery site and there is plenty of discussion on this, including using 50/50 as a deco gas. The 2 bits I remember are that it provides a cleaner deco as there is an even bigger gas gradient and the bottle rides better. I am sure someone with far more experience will be along to explain more... __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

October 31st, 2006, 04:46 PM	#3 (permalink)
Ahmed Adly, Marlin Inn DC(Offline) New Member Join Date: Feb 2006 Location: hurghada Posts: 849	50/25 rides well. That is the main reason it is used. But there is some suspicion about the deco thingy too. Ahmed __________________ It has just dawned on me.... We are all just recycled stardust Ahmed Adly, www.deepvoyage.com

October 31st, 2006, 04:51 PM	#4 (permalink)
Gareth Burrows(Offline) Chimp 2 Join Date: Nov 2005 Location: Horsham, West Sussex Posts: 365	Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC) 50/25 rides well. That is the main reason it is used. But there is some suspicion about the deco thingy too. Ahmed that's the most succinct and accurate expression of the DIR ethos I've ever seen. :D __________________ Garf Amusing and Clever Signature under construction.

October 31st, 2006, 06:54 PM	#6 (permalink)
Janos(Offline) "Two Sheds" Join Date: Nov 2005 Location: Surrey Posts: 400	I looked at this for a while. There's a fair bit over on The Deco Stop. And there's a thread I started on RBW. My conclusion is that many people find 50/25 or 50/50 leaves them feeling better following a dive. However all the cases I saw where two (or more) stage dives where they used O2 at the final stage. The point here is that pure O2 is an He free gas; and He being "quick" gets out the system quicker. Have a look at that Richard Pyle article (the one where he advocates deep stops 20m above the bottom, not 80%). Later on he talks about the relatively off gassing of different inerts and it all makes sense. I decided against putting He in my shallow bottle (to make it ride better) as I wouldn't be finishing deco on O2 and I was worried about residual He. Janos __________________ You can lead a horse to water but you can't climb a ladder with a large bell in both hands - Vic Reeves www.hellfins.com/shed

October 31st, 2006, 05:07 PM	#5 (permalink)
*Bob Cooper*(Offline) Moderator - "Don't stop me now!" Join Date: Nov 2005 Location: South East London, UK Posts: 680	Quote: (Originally Posted by Divingniknaks) Just wondered what the more experienced amongst you thought to that as a "deco" gas v the "normal" 50%. The helium make the deco bottles closer to neutral when full. There are also advantages to using some helium in the deco mix.

October 31st, 2006, 07:25 PM	#7 (permalink)
Hassan Adly(Offline) GUE Instructor Join Date: Feb 2006 Location: Red Sea Posts: 287	Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC) 50/25 rides well. That is the main reason it is used. Hang on, before making sweeping statements like that let's see what the people who actually use it think... Quote: But there is some suspicion about the deco thingy too There are quite clear reasons for using 50/25 or 50/50 as compared to 50% nitrox, and having a neutrally buoyant cylinder isn't the main reason. Simply put, when you put helium in the 21m cylinder, you are reducing the nitrogen component and hence increasing the nitrogen gradient. This leads to more efficient offgassing of nitrogen as compared to 50% nitrox. This explains why people "feel" better after using 50/25 or 50/50. Using helium in the 21m cylinder also means that we decrease the helium gradient and offgas helium more slowly, which is something that has to be accounted for in the deco profile - which is why you would normally see this gas used in conjunction with oxygen, where the "fast helium" effect comes into play. 50% nitrox is for when you want to get the helium out. 50/25 or 50/50 is for when you want to get the nitrogen out! __________________ 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 Last edited by Hassan Adly; October 31st, 2006 at 07:35 PM.

October 31st, 2006, 08:38 PM	#8 (permalink)
jluttichau(Offline) Custom User Title Join Date: Nov 2005 Location: Denmark Posts: 437	Quote: (Originally Posted by Garf) that's the most succinct and accurate expression of the DIR ethos I've ever seen. :D Why DIR: It rides well and theres something about the deco thingy too.. Cheers

October 31st, 2006, 08:48 PM	#9 (permalink)
GLOC (Online) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,963	Quote: (Originally Posted by Ahmed Adly, Marlin Inn DC) 50/25 rides well. That is the main reason it is used. Quote: (Originally Posted by Hassan Adly) Hang on, before making sweeping statements like that let's see what the people who actually use it think... You 2 sound like Garf and I! __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

October 31st, 2006, 11:16 PM	#10 (permalink)
lizardland(Offline) LCS Join Date: Nov 2005 Location: Evidently Chickentown Posts: 593	It's advantageous in long decos to have a bit of helium, it's increasing the nitrogen gradient as stated, it's easier to breathe on long stops and (for whatever physiological reason) I think it makes you feel better. With a long bottom time on trimix then a switch to straight nitrox isn't a particularly good idea either. On normalish deco dives I don't think there is much advantage, maybe even counter-productive. You will need to offgas the helium at some point, on a short deco then this may increase your deco time. I generally breathe helium in my mix all the way up (one benefit of diving a rebreather ) but I always make sure I do full flushes at 6m so that I'm on pure O2 for the final stop. __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk The Lot isn't the only place to dive: http://www.lulu.com/content/613554