Trimix...

[MookieMoose]

Helium has very little thermal values, so you will get cold quicker than on air.

This is a bit of a misnomer - Helium has very high thermal conductivity, so it will carry heat away from your body faster, ie. it is a poor insulator, so it should not be used to inflate your drysuit.

The kicker is that helium also has a very low specific heat, it is not capable of absorbing very much heat into the gas. Since gas breathed into your lungs is always heated to body temp, the specific heat is more important when talking about breathing gasses - how much energy does your body have to spend in order to heat the inhaled gas to body temp. Since helium has a lower specific heat than nitrogen, you actually loose less heat by breathing helium than you do breathing nitrogen.

Now, because helium is less dense than nitrogen, it can feel like it's cooler when inhaling vs. nitrogen, but that feeling does not reflect heat loss, it's a trick, and only a product of density. The long and short is you will loose heat faster with helium in your drysuit, but will retain more heat with helium in your breathing gas when compared to nitrogen.

Cam

 

[wedivebc]

Example: I use different trimix mixes for planned dives

15/25 for 200 feet 15O2/25HE
14/33 for 300 feet
10/52 for 400 feet
8/64 for sub 400

All these mixes are Heliair (helium topped with air) Why, because its easy and accurate to mix and I have diving it for 15 years. So I know it works.

.

Curt, did you use these mixes when diving OC as well?

 

[mer]

Helium is very expensive and only comes in LP bank cylinders 2400 psi.

Nope, both Linde Gas and Air Gas (and most likely others) have it available in 3500 and 6000 psi. It is often a special order requiring 3-7 days of lead time.

 

[padiscubapro]

This is a bit of a misnomer - Helium has very high thermal conductivity, so it will carry heat away from your body faster, ie. it is a poor insulator, so it should not be used to inflate your drysuit.

The kicker is that helium also has a very low specific heat, it is not capable of absorbing very much heat into the gas. Since gas breathed into your lungs is always heated to body temp, the specific heat is more important when talking about breathing gasses - how much energy does your body have to spend in order to heat the inhaled gas to body temp. Since helium has a lower specific heat than nitrogen, you actually loose less heat by breathing helium than you do breathing nitrogen.

Now, because helium is less dense than nitrogen, it can feel like it's cooler when inhaling vs. nitrogen, but that feeling does not reflect heat loss, it's a trick, and only a product of density. The long and short is you will loose heat faster with helium in your drysuit, but will retain more heat with helium in your breathing gas when compared to nitrogen.

Cam

You beat me to the response! check out my response on this thread

http://www.scubaboard.com/showthread.php?t=100129


also see the thread
http://www.scubaboard.com/showthread.php?t=83987&highlight=thermal+conductivity

I go over all the properties and reasons for heat loss in breathing mixes.. Sorry Curt your wrong about breathing helium makes you lose more heat, in your lungs it just feels taht way because the He molecules take on the heat much more rapidy, but in the end the net loss from BREATHING is less...

 

[Curt Bowen]

Curt, did you use these mixes when diving OC as well?

Thats all I use on OC. For CCR I normally use 10/52 only. Why, because I have several hundred cuft banked in my dive trailer. Thats the only reason.

 

[Curt Bowen]

You beat me to the response! check out my response on this thread

http://www.scubaboard.com/showthread.php?t=100129


also see the thread
http://www.scubaboard.com/showthread.php?t=83987&highlight=thermal+conductivity

I go over all the properties and reasons for heat loss in breathing mixes.. Sorry Curt your wrong about breathing helium makes you lose more heat, in your lungs it just feels taht way because the He molecules take on the heat much more rapidy, but in the end the net loss from BREATHING is less...

Really, I guess all those thousands or dives I froze my *** off, was just in my head. Maybe I would have froze just as much with air?

 

[Curt Bowen]

Nope, both Linde Gas and Air Gas (and most likely others) have it available in 3500 and 6000 psi. It is often a special order requiring 3-7 days of lead time.

Wonder why Tritek, my gas company never told me about that offer? Is it the same price per cuft or more? It would be nice to get a 3500 psi bank.