Gradient Factors - Air Dil vs Trimix Dil

athomson · 2nd May 2008, 12:38

I've a question for anyone out there who can give me staright answer.

I've been diving rebreathers for over a year and have just completed my Mod 2 in Malin Head. Yes, April in the North Atlantic and it was f$&%*ing freezing! Great course but may not have been the best time of year for it.

Anyway, I'm still trying to get a better understanding of gradient factors at the moment with regard to air dil and trimix dil. Until recently, I dived the Vision Nitrox Software with a conversatism setting of 3, which is 90/90, so fairly close to Bulhmans. With the trimix software now installed, I've started diving with 20/80 GF set. I'm still jumping back and forth a bit between the trimix and air dil depending on the dive. However, I have noticed that if I do an air dil dive with 20/80, I feel crappy after the dive (aches, pains, and generally cream-crackered) while I feel generally fine after a trimix dive. Now, I've started diving the 90/90 for air again .. no problems.

What I'm trying to understand is why this is. I would think that the 20/80 is more conservative and hence better for me. I've also sent this question by email to my Mod 2 instructor so if I get an answer from there, I'll post it.

Any comments or ideas would be welcome.

Regards,

Andy T

***EBT*** · 2nd May 2008, 13:55

'what works, works'... is the glib reply. The longer reply is that maybe you need to show a profile, or at least the other parameters ie;

- ascent/descent rates
- PO2's on bottom/deco.

***ScubaDadMiami*** · 2nd May 2008, 18:13

With the low GF set to 20, you might actually still be ingassing at your deepest stop to the point where you will need to pull longer shallow stops. This is why 10/100 or 10/90 is considered very aggressive.

Mark Chase · 2nd May 2008, 18:51

Quote: (Originally Posted by athomson)

I've a question for anyone out there who can give me staright answer.

I've been diving rebreathers for over a year and have just completed my Mod 2 in Malin Head. Yes, April in the North Atlantic and it was f$&%*ing freezing! Great course but may not have been the best time of year for it.

Anyway, I'm still trying to get a better understanding of gradient factors at the moment with regard to air dil and trimix dil. Until recently, I dived the Vision Nitrox Software with a conversatism setting of 3, which is 90/90, so fairly close to Bulhmans. With the trimix software now installed, I've started diving with 20/80 GF set. I'm still jumping back and forth a bit between the trimix and air dil depending on the dive. However, I have noticed that if I do an air dil dive with 20/80, I feel crappy after the dive (aches, pains, and generally cream-crackered) while I feel generally fine after a trimix dive. Now, I've started diving the 90/90 for air again .. no problems.

What I'm trying to understand is why this is. I would think that the 20/80 is more conservative and hence better for me. I've also sent this question by email to my Mod 2 instructor so if I get an answer from there, I'll post it.

Any comments or ideas would be welcome.

Regards,

Andy T

In the very broadest of terms....

Trimix uses Helium and Helium deco benefits from deeper stops so its better to do more deep stops on trimix than on air.

Empirical data? I have never seen any one in the water bent on Nitrogen but I have witnessed divers bent on the 6m stop due to helium.

So an aggressive trimix deco for me is 30/120GF but and aggressive Air deco is 100/100

As for you're diving... try going pure 02 for the last 20mins of ANY deco. It worked wonders for me.

ATB

Mark

2nd May 2008, 12:38	#1 (permalink)
athomson New Member Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Oct 2006 Location: Dublin Posts: 9	Gradient Factors - Air Dil vs Trimix Dil I've a question for anyone out there who can give me staright answer. I've been diving rebreathers for over a year and have just completed my Mod 2 in Malin Head. Yes, April in the North Atlantic and it was f$&%*ing freezing! Great course but may not have been the best time of year for it. Anyway, I'm still trying to get a better understanding of gradient factors at the moment with regard to air dil and trimix dil. Until recently, I dived the Vision Nitrox Software with a conversatism setting of 3, which is 90/90, so fairly close to Bulhmans. With the trimix software now installed, I've started diving with 20/80 GF set. I'm still jumping back and forth a bit between the trimix and air dil depending on the dive. However, I have noticed that if I do an air dil dive with 20/80, I feel crappy after the dive (aches, pains, and generally cream-crackered) while I feel generally fine after a trimix dive. Now, I've started diving the 90/90 for air again .. no problems. What I'm trying to understand is why this is. I would think that the 20/80 is more conservative and hence better for me. I've also sent this question by email to my Mod 2 instructor so if I get an answer from there, I'll post it. Any comments or ideas would be welcome. Regards, Andy T
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2nd May 2008, 13:55	#2 (permalink)
*EBT* Apprentice Luddite Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Feb 2005 Location: UK, Brighton Posts: 1,855	Re: Gradient Factors - Air Dil vs Trimix Dil 'what works, works'... is the glib reply. The longer reply is that maybe you need to show a profile, or at least the other parameters ie; - ascent/descent rates - PO2's on bottom/deco. __________________ Eagles May Soar, but weasels don't get sucked into jet engines! Rebreather World Terms of service Real diving t-shirts for real divers
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2nd May 2008, 18:13	#3 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,937	Re: Gradient Factors - Air Dil vs Trimix Dil With the low GF set to 20, you might actually still be ingassing at your deepest stop to the point where you will need to pull longer shallow stops. This is why 10/100 or 10/90 is considered very aggressive. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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2nd May 2008, 18:51	#4 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,470	Re: Gradient Factors - Air Dil vs Trimix Dil Quote: (Originally Posted by athomson) I've a question for anyone out there who can give me staright answer. I've been diving rebreathers for over a year and have just completed my Mod 2 in Malin Head. Yes, April in the North Atlantic and it was f$&%ing freezing! Great course but may not have been the best time of year for it. Anyway, I'm still trying to get a better understanding of gradient factors at the moment with regard to air dil and trimix dil. Until recently, I dived the Vision Nitrox Software with a conversatism setting of 3, which is 90/90, so fairly close to Bulhmans. With the trimix software now installed, I've started diving with 20/80 GF set. I'm still jumping back and forth a bit between the trimix and air dil depending on the dive. However, I have noticed that if I do an air dil dive with 20/80, I feel crappy after the dive (aches, pains, and generally cream-crackered) while I feel generally fine after a trimix dive. Now, I've started diving the 90/90 for air again .. no problems. What I'm trying to understand is why this is. I would think that the 20/80 is more conservative and hence better for me. I've also sent this question by email to my Mod 2 instructor so if I get an answer from there, I'll post it. Any comments or ideas would be welcome. Regards, Andy T In the very broadest of terms.... Trimix uses Helium and Helium deco benefits from deeper stops so its better to do more deep stops on trimix than on air. Empirical data? I have never seen any one in the water bent on Nitrogen but I have witnessed divers bent on the 6m stop due to helium. So an aggressive trimix deco for me is 30/120GF but and aggressive Air deco is 100/100 As for you're diving... try going pure 02 for the last 20mins of ANY deco. It worked wonders for me. ATB Mark __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System*
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