Modern research/thoughts on Ascent Rates

[grantctobin]

I am out of my depth here not being a rebreather diver, but everyone I've seen uses larger diluent tanks like 7 liter minimum. Little 3 liter tanks don't leave much margin for error if you have a gas leak or something.
But regardless of tank size, why the concern over expense? Are we talking like $1 worth of gas here? Maybe $2? So what.

Actually argon, but whatever. I don't see a problem with inflating a small DSMB using the drysuit inflator hose since at the end of the dive you shouldn't need to add any more gas to the drysuit. It works fine with a small DSMB and I do it myself sometimes because my lips get so cold on long dives that I have trouble orally inflating a closed circuit DSMB. With a large DSMB, the little drysuit inflation tank might not have enough gas left in it. Some divers attach an extra inflator hose to their left post and use that for filling DSMBs or lift bags. I'm not sure what the best approach is here?

Agreed.

if we include all CCR divers (incl sidemount ccr, dilout, things like sidewinder and choptima with doubles, gue rack, RB80 racks etc) on a per unit basis, I'd guess average diluent size is still between 3 and 4L, though the number of larger diluent users is increasing because of things like the sidewinder and choptima and racks

 

[Wibble]

Who uses argon to inflate a drysuit?

Is it more expensive than helium?

Air works very well, costs next to nothing, is readily available and doesn’t need special handling — dedicated tins, etc.

 

[Manatee Diver]

When I asked about argon "Just use air" was the response I got around here. I'm not even sure any of the tech shops even fill argon.

 

[Nick_Radov]

Who uses argon to inflate a drysuit?

This has been common practice among some US technical divers for 20+ years. In California and Washington, several of the local dive shops fill argon but it might be hard to obtain in other places.

Is it more expensive than helium?

Argon is cheaper than helium, but who cares? We use so little of it per dive (even with filling a small DSMB) that the cost is trivial.

Air works very well, costs next to nothing, is readily available and doesn’t need special handling — dedicated tins, etc.

Argon has a thermal conductivity about 30% lower than air so it works slightly better, although any actual difference in body heat loss is probably small. Subjectively it seems to help a little on long dives. Or maybe it's just a placebo effect?

 

[Wibble]

I appreciate that a very few people may use it. Nobody I’ve ever met though.

There’s so few technical dive shops nowadays, but have never found one that sells argon.

 

[Akimbo]

Who uses argon to inflate a drysuit?

This has been common practice among some US technical divers for 20+ years. In California and Washington, several of the local dive shops fill argon but it might be hard to obtain in other places.

This practice has been dying out quickly. It is true that Argon has a little lower thermal conductivity than air, WHEN DRY. The fallacy is comparing these values to the very high humidity in a drysuit (from perspiration).

Thermal Conductivity Relative to Air​

Relative Conductivity	W/(m·K)​	Name
1.0​	0.024​	Air (gas)
0.7​	0.016​	Argon (gas)
0.6​	0.0146​	Carbon dioxide (gas)
5.9​	0.142​	Helium (gas)
7.0​	0.168​	Hydrogen (gas)
90.8​	2.18​	Ice (0°C, 32°F)
1.0​	0.024​	Nitrogen
1.0​	0.024​	Oxygen
24.2​	0.58​	Water

 

[inquis]

We use so little of it [argon] per dive

Which is why it is typically no better than air. To really leverage the superior thermal properties, you need to flush your suit a few times to remove most of that air.

 

[Nick_Radov]

Which is why it is typically no better than air. To really leverage the superior thermal properties, you need to flush your suit a few times to remove most of that air.

Yes we do flush our drysuits a few times at the surface. That still doesn't take much argon. You can flush your suit, do a deep technical dive, inflate a small DSMB, and still have gas left in a little 6 ft³ tank.
I think argon does help me stay warm, although I don't have a way to prove it.

 

[Wibble]

Drysuits do get damp due to perspiration and leaks. This is why you need to hang up your underclothes overnight to dry them.

Or, to be blunt, if you bag them up after a dive and leave them for a couple of days, they stink.

Secondly, if you’re a bit light — some may say ‘correctly' weighted— the suit will be rather snug thus relying more on the insulation properties of your undersuit. In any case the gas will migrate to your back due to hydrostatic pressure differentials between your front and back. Some people wear a door mat for insulation on their chest.

The main reason for using a separate suit inflation bottle is to keep helium out of the drysuit. It’s extremely rare for someone to use argon when air is so much more practical.

 

[Akimbo]

The main reason for using a separate suit inflation bottle is to keep helium out of the drysuit. It’s extremely rare for someone to use argon when air is so much more practical.

Helium is not only more expensive, it is 5.9 times more thermally conductive than air. A real loose-loose option for drysuit equalization. Argon is only 0.7 times as thermally conductive. Of course humidity in the suit makes both gasses significantly more conductive.

Lower cost, reduced HPNS, and lower thermal conductivity are the advantages of Trimix over HeO2. Saturation divers use HeO2 but have hot water heated wetsuits and add gas heaters below 600', and often shallower. Thermal loss for sat divers is estimated at about 50% through respiration alone.