Trimix Versus HeliOx and Deco time

Lancer4545 · 2nd May 2008, 07:44

I had an interesting discussion recently regarding gas consumption and deco time when diving on HeliOx as compared to diving with Trimix.

It came about when we were on our last deep wreck trip and the guys were working out our Helium consumption and then comparing that to what they expected the HeliOx divers would use.

I ran the profiles through my planning software and always came up with longer deco and run times compared to the mix we were on.

Our mix was 16/45 and the Heliox guys were going to use 10/90 for the same 75m dives.

I got a reply back the other day and nearly fell off my chair when I saw what these guys were diving.

<paste>

As promised (names withheld) did all the blending and they used hardly any He at all- those blokes really know what they're on.

they boosted a little O2 on top of a full cylinder of He and then topped off Dil tanks as required. they were diving 40-60mins bottom, 200 mins total run max

We were doing similar bottom times to these and were coming up with total run time nearly an hour longer. Plug their mix in and the end result is over another hour deco longer.

Is there something I am missing here or is someone blazing a new (and dangerous) trail?

Regards,

Lance

ADDED Please, Please......Lets not turn this into a bashing place and lets keep it on subject!!

**DeepBlueInnovation** · 2nd May 2008, 07:54

Sounds aggressive; if you plug it into v-planner (and I don't want to re-start the debate from other threads) with nominal conservatism and switching to 100% @6m it comes out with a 209min runtime on the 10/90.

Cheers,

Ben.

Lancer4545 · 2nd May 2008, 08:31

Quote: (Originally Posted by DeepBlueInnovation)

Sounds aggressive; if you plug it into v-planner (and I don't want to re-start the debate from other threads) with nominal conservatism and switching to 100% @6m it comes out with a 209min runtime on the 10/90.

Cheers,

Ben.

Hi Ben,

I came up with a run time of 239mins from our actual dive plans. Plug in the HeliOx and the run time jumps to 313mins.

Lance

**DeepBlueInnovation** · 2nd May 2008, 08:42

Sorry mate, don't know why the difference. I set the profile up with 5 day prior surface interval, 40min @75m on 10/90 and 1.3 set-point. The only gas switch was to 100% 02 @6m. The schedule is attached below.

sample_profile.doc

Cheers,

Ben.

lizardland · 2nd May 2008, 09:11

Running it through the M11F6 model gives 238min of deco for heliox on the profile described:

0m >> 75m 3min; Hx10 RT: 3min
75m >> 75m 37min; Hx10 RT: 40min

Decompression Plan
198min of deco.

1.3 set point, O2 switch at 6m.

**nigelh** · 2nd May 2008, 09:18

I just punched the numbers into a raw Bühlmann CCR engine
and for 3mins descent and ascend at 43mins runtime
with a final 6m stop on 1.3 I got:

14/60 run 166mins
16/65 run 170mins
10/90 run 184mins

Some people don't like Bühlmann's numbers for Helium and wonder if he would have revised them but he didn't. Basically he makes it a faster gas and more prone to bubble so you need to gas down the compartment further. More helium on a Bühlmann model, once you're over about 30%, costs you more time. Remember there is zero conservatism built in to those numbers.

Frankly the only advantage I see in heliox is that you don't have to analyse it.

(edit) Well the line above wasn't at all what I meant. It looks more stupid every time I read it. See below. (/edit)

Lancer4545 · 2nd May 2008, 09:40

Here is my actual dive plan on TriMix followed by the HeliOx

POOF......

It isn't a matter of the exact numbers in your coming up with. The point I am making is, most dive planning software will come up with a lot longer deco for HeliOx dives than those on TriMix..........

Regards,

Lance

Lancer4545 · 2nd May 2008, 09:43

Quote: (Originally Posted by nigelh)

Frankly the only advantage I see in heliox is that you don't have to analyse it.

Oh.....how do you fugure out the percentages ????

***Beanie*** · 2nd May 2008, 09:50

Quote: (Originally Posted by Lancer4545)

Oh.....how do you fugure out the percentages ????

same as you would nitrox, there's only two gases so measure on of them (Oxygen)

solocavediver · 2nd May 2008, 09:53

Let's note that Heliox takes longer on VPM, so it clearly isn't just Dr. Buhlmann who reckons longer deco on 10/90.

The mathematical reason (for VPM) is that VPM works by (as far as possible) holding the supersaturation pressure constant in your tissues (NB it's NOT exactly possible to do this for all compartments at once, but VPM gets as close as it can to this). Helium comes out early, Nitrogen comes out late; so you can spread the decompression process more evenly throughout your ascent by using a mixture of N2 and He as diluent, and that results in shorter deco.

Cheers,

Charles.

2nd May 2008, 07:44	#1 (permalink)
Lancer4545 Closed Circuit Divers Aus Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jun 2007 Location: Cairns QLD Australia Posts: 534	Trimix Versus HeliOx and Deco time I had an interesting discussion recently regarding gas consumption and deco time when diving on HeliOx as compared to diving with Trimix. It came about when we were on our last deep wreck trip and the guys were working out our Helium consumption and then comparing that to what they expected the HeliOx divers would use. I ran the profiles through my planning software and always came up with longer deco and run times compared to the mix we were on. Our mix was 16/45 and the Heliox guys were going to use 10/90 for the same 75m dives. I got a reply back the other day and nearly fell off my chair when I saw what these guys were diving. <paste> As promised (names withheld) did all the blending and they used hardly any He at all- those blokes really know what they're on. they boosted a little O2 on top of a full cylinder of He and then topped off Dil tanks as required. they were diving 40-60mins bottom, 200 mins total run max We were doing similar bottom times to these and were coming up with total run time nearly an hour longer. Plug their mix in and the end result is over another hour deco longer. Is there something I am missing here or is someone blazing a new (and dangerous) trail? Regards, Lance ADDED Please, Please......Lets not turn this into a bashing place and lets keep it on subject!! __________________ You can run but you can't hide! ISC Appointed Megalodon Dealer for East Australia http://www.closedcircuitdivers.com.au info@closedcircuitdivers.com.au Last edited by Lancer4545 : 2nd May 2008 at 08:34. Reason: sp
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2nd May 2008, 07:54	#2 (permalink)
DeepBlueInnovation Prism #007 Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Sep 2005 Location: Perth, Western Australia Posts: 291	Re: Trimix Versus HeliOx and Deco time Sounds aggressive; if you plug it into v-planner (and I don't want to re-start the debate from other threads) with nominal conservatism and switching to 100% @6m it comes out with a 209min runtime on the 10/90. Cheers, Ben.
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2nd May 2008, 08:31	#3 (permalink)
Lancer4545 Closed Circuit Divers Aus Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jun 2007 Location: Cairns QLD Australia Posts: 534	Re: Trimix Versus HeliOx and Deco time Quote: (Originally Posted by DeepBlueInnovation) Sounds aggressive; if you plug it into v-planner (and I don't want to re-start the debate from other threads) with nominal conservatism and switching to 100% @6m it comes out with a 209min runtime on the 10/90. Cheers, Ben. Hi Ben, I came up with a run time of 239mins from our actual dive plans. Plug in the HeliOx and the run time jumps to 313mins. Lance __________________ You can run but you can't hide! ISC Appointed Megalodon Dealer for East Australia http://www.closedcircuitdivers.com.au info@closedcircuitdivers.com.au
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2nd May 2008, 08:42	#4 (permalink)
DeepBlueInnovation Prism #007 Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Sep 2005 Location: Perth, Western Australia Posts: 291	Re: Trimix Versus HeliOx and Deco time Sorry mate, don't know why the difference. I set the profile up with 5 day prior surface interval, 40min @75m on 10/90 and 1.3 set-point. The only gas switch was to 100% 02 @6m. The schedule is attached below. sample_profile.doc Cheers, Ben.
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2nd May 2008, 09:11	#5 (permalink)
lizardland Yak Current Rebreather/s: Classic Kiss Ray Home Build Other Rebreather/s: Ray Home Build Join Date: Mar 2005 Location: North... Posts: 1,138	Re: Trimix Versus HeliOx and Deco time Running it through the M11F6 model gives 238min of deco for heliox on the profile described: 0m >> 75m 3min; Hx10 RT: 3min 75m >> 75m 37min; Hx10 RT: 40min Decompression Plan 198min of deco. 1.3 set point, O2 switch at 6m. __________________ 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 Azerbaijani Association of Technical Divers Publicity Officer and Goat Wrangler
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2nd May 2008, 09:18	#6 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 784	Re: Trimix Versus HeliOx and Deco time I just punched the numbers into a raw Bühlmann CCR engine and for 3mins descent and ascend at 43mins runtime with a final 6m stop on 1.3 I got: 14/60 run 166mins 16/65 run 170mins 10/90 run 184mins Some people don't like Bühlmann's numbers for Helium and wonder if he would have revised them but he didn't. Basically he makes it a faster gas and more prone to bubble so you need to gas down the compartment further. More helium on a Bühlmann model, once you're over about 30%, costs you more time. Remember there is zero conservatism built in to those numbers. Frankly the only advantage I see in heliox is that you don't have to analyse it. (edit) Well the line above wasn't at all what I meant. It looks more stupid every time I read it. See below. (/edit) __________________ nigelh Last edited by nigelh : 2nd May 2008 at 12:29.
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2nd May 2008, 09:40	#7 (permalink)
Lancer4545 Closed Circuit Divers Aus Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jun 2007 Location: Cairns QLD Australia Posts: 534	Re: Trimix Versus HeliOx and Deco time Here is my actual dive plan on TriMix followed by the HeliOx POOF...... It isn't a matter of the exact numbers in your coming up with. The point I am making is, most dive planning software will come up with a lot longer deco for HeliOx dives than those on TriMix.......... Regards, Lance __________________ You can run but you can't hide! ISC Appointed Megalodon Dealer for East Australia http://www.closedcircuitdivers.com.au info@closedcircuitdivers.com.au Last edited by Lancer4545 : 2nd May 2008 at 12:15. Reason: Removed Plans
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2nd May 2008, 09:43	#8 (permalink)
Lancer4545 Closed Circuit Divers Aus Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jun 2007 Location: Cairns QLD Australia Posts: 534	Re: Trimix Versus HeliOx and Deco time Quote: (Originally Posted by nigelh) Frankly the only advantage I see in heliox is that you don't have to analyse it. Oh.....how do you fugure out the percentages ???? __________________ You can run but you can't hide! ISC Appointed Megalodon Dealer for East Australia http://www.closedcircuitdivers.com.au info@closedcircuitdivers.com.au Last edited by Lancer4545 : 2nd May 2008 at 09:48.
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2nd May 2008, 09:50	#9 (permalink)
*Beanie* Cheif tea maker Current Rebreather/s: Inspiration Classic Other Rebreather/s: Inspiration Vision Join Date: Jan 2005 Location: In da house! yeah baby! Posts: 3,134	Re: Trimix Versus HeliOx and Deco time Quote: (Originally Posted by Lancer4545) Oh.....how do you fugure out the percentages ???? same as you would nitrox, there's only two gases so measure on of them (Oxygen) __________________ Beanie Gallery Admin & Library Assistant. www.outlawdivers.org.uk www.beandiving.co.uk www.beanengineering.co.uk www.divelife.co.uk
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2nd May 2008, 09:53	#10 (permalink)
solocavediver New Member Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Apr 2006 Location: Leeds UK Posts: 98	Re: Trimix Versus HeliOx and Deco time Let's note that Heliox takes longer on VPM, so it clearly isn't just Dr. Buhlmann who reckons longer deco on 10/90. The mathematical reason (for VPM) is that VPM works by (as far as possible) holding the supersaturation pressure constant in your tissues (NB it's NOT exactly possible to do this for all compartments at once, but VPM gets as close as it can to this). Helium comes out early, Nitrogen comes out late; so you can spread the decompression process more evenly throughout your ascent by using a mixture of N2 and He as diluent, and that results in shorter deco. Cheers, Charles.
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