Trimix Sac Rate - slightly higher?

[BabyLitigator]

Just did my first trimix dives (Farnsworth Bank which is awesome if a LOOOONG day). Noticed my SAC rate was a bit (~10%) higher than my more recent dives, based on comparable perceived level of effort. Is this a trimix thing, or just the day? Google AI said it was a Trimix thing but who knows.

 

[lermontov]

cant say ive noticed it in relation to trimix -if its you first trimix dive then perhaps you were more tense than usual? or where you carrying more gear ( drag)
even a slight anxiety can change your SAC even if your not consciously feeling anxious - i know my sac rate goes up when I go to a new site and not sure what to expect

 

[boulderjohn]

If all your gear is the same, I would guess it is your task loading with new skills, etc. To get your best SAC rate, you need to be relaxed, and you are not likely to be relaxed under those circumstances.

 

[broncobowsher]

My theory, thermal stress. Helium transfers more heat.
That would be if everything else was identical, and your thermal managment was right at the edge of where consumption increases, even if you are still comfortable.

 

[Germie]

I think this is because you was nervous for your first trimixdives. I have never mentioned a higher RMV/SAC.
A lot of people have a little bit higher consumption when something is new. So it is not strange. Don't worry too much, relax and enjoy your diving.

 

[sea_ledford]

Depending on how you calculated your SAC, it also might be as simple as the tanks were sitting in the sun for the whole ride out, so they were warmer when you jumped in the water. Rapid cooling back to "normal" pressure would show up as increased SAC.

 

[pickens_46929]

One dive does not make a trend nor is it statistically significant. Do another 20 Trimix dives to see if the +10% remains a constant.

 

[Kendall Raine]

Various counter current factors. Thermal issues of breathing helium may be less of an issue than previously thought: Fighting Exposure – Is Helium a “cold” gas? -. Not the case for helium in suit inflation, of course, but who does that?

Furthermore, mechanical efficiency of using high helium v nitrogen mixes on WoB argue against increased SAC. More likely issue is (as others have suggested) emotional/stress related. Transitioning to helium mixes means diving deeper, with deco, and all the additional equipment and deco planning that involves. In summary, do 100 helium dives and track the SAC (electronically if possible) before making conclusions.

 

[BabyLitigator]

I think this is because you was nervous for your first trimixdives. I have never mentioned a higher RMV/SAC.
A lot of people have a little bit higher consumption when something is new. So it is not strange. Don't worry too much, relax and enjoy your diving.

Figured it out. We switched back to back gas after deco was done and then did drills. Subsurface says my sac rate was awful at that point and that brought the overall rate up.

 

[Germie]

With drills it is quite normall that the sac/rmv is a little bit higher.

I talk about sac/rmv as a lot of people talk about sac in liters per minute, but officially this is the rmv.