Opinions on DSAT TecRec courses

[JeffG]

There is always the issue of temperature loss to deal with when breathing Helium.

Well, according to 36 Myths of Diving Physiology and The Case For Heliox : A Matter of Narcosis and Economics


unless you are using the Helium in your drysuit.

20. COLDER BREATHING HELIUM?
There is much discussion whether you get colder breathing helium than breathing air. Helium has greater thermal conductivity than air. Undeniably, you lose more heat when surrounded by helium than by air, because heat conductance is the major factor in skin heat loss. Therefore helium is not used in dry suits. However, respiratory heat loss depends on heat capacity, and not at all on conductance. The thermal capacity of helium per gram is higher than that of air. However, there are fewer grams of helium for the same volume breathed because it is far less dense, making thermal capacity less compared to the same volume of air. Less heat would be lost breathing helium, so it should not chill you to breathe, as commonly thought. In a helmet or full face mask, your face may feel cool, making it hard to separate out the lesser loss through breathing.
Depth affects gas density, and so, heat loss through the breathing medium, and to be more confusing, you also need to account for interactions of respiratory heat loss through convection and evaporation. With helium you may also be more aware of the cold that is so common in diving, than when dulled by narcosis while breathing non-helium mixes. Remember too, it is generally not feasible to breathe air at depths where helium is used, so hard to compare in actual use. The short answer seems to be that breathing mixtures of helium at depths encountered by technical divers does not seem to result in greater cooling than breathing air. Helium feels colder to your skin than air, but it carries away less heat when you breathe it. So there.

A good case can be made that because of the greatly reduced density (and consequently thermal capacity) of helium, convective heat losses for helium mixtures are probably less that that for compressed air (and other nitrogen mixtures) at any given depth

 

[JeffG]

How long is your extension cord?

~18 in

 

[DCBC]

Well, according to ... unless you are using the Helium in your drysuit.

The heat that's lost, is primarily lost through the breathing process. The respiratory heat loss increases from about 10 percent of the body’s heat generating capacity at the surface to 28 percent at 7 ATA and 50 percent at 21 ATA when breathing Heliox. This is why in commercial diving the breathing mixture is preheated.

PS

Additionally, approx 10-12% of heat loss (from a non-sweating diver) comes from the head. This is exposed to Helium as a result of the Superlite. This adds to the Helium heat-sink. Prolonged exposure to breathing Helium requires that the diver use a hot-water suit.

Although Argon is often used as a dry suit inflation gas, our tests at DCIEM showed mixed results. Argon increases urinary output. As such it increases heat loss and dehydration (which causes another problem), however the thermal conductivity of Argon is about 30% less than air.

 

[JeffG]

as a result of the Superlite.

Whats that?

 

[DCBC]

Whats that?

The helmet the diver wears which includes the regulator.

 

[JeffG]

The helmet the diver wears which includes the regulator.

Ah. Thanks. Never heard that term before. (Mind you I know very little about commercial diving, period.)

 

[Blackwood]

Argon increases urinary output. As such it increases heat loss

I remember learning once that your body flushes un-necessary fluids so it doesn't have as much volume to keep warm.

 

[boomx5]

Additionally, approx 10-12% of heat loss (from a non-sweating diver) comes from the head. This is exposed to Helium as a result of the Superlite. This adds to the Helium heat-sink. Prolonged exposure to breathing Helium requires that the diver use a hot-water suit.

I know we've hijacked this thread and maybe it should be split off but, in your studies did you find that the hot water suit did anything to the decompression? I know Jeff uses a heated vest, and I know of other people who use or have used heated vests with mixed results. From what I've heard it gives them weird results on the decompressions. Maybe it's because the heat is not distributed efficiantly throughout the body and it's extremities. I'm just curious, any thoughts?

 

[DCBC]

I know we've hijacked this thread and maybe it should be split off but, in your studies did you find that the hot water suit did anything to the decompression? I know Jeff uses a heated vest, and I know of other people who use or have used heated vests with mixed results. From what I've heard it gives them weird results on the decompressions. Maybe it's because the heat is not distributed efficiantly throughout the body and it's extremities. I'm just curious, any thoughts?

I agree; it seems that we are getting off of the discussion. Hot water suits don't change the decompression profile.

The suit does however increase sweating and fluid loss; which leads to isotonic dehydration. This requires the diver to take a break for fluid intake periodically. When you're saturated and working in the water, the maximum time you work is 2 hours. If the saturated diver works in an underwater habitat (used for dry welding) he usually has an eight hour shift.

 

[Hyper-limits]

There is always the issue of cost and temperature loss to deal with when breathing Helium. I'd be interested in hearing how divers who are diving in cold water to 300' deal with that one.

CCR I found that I can stay in the water a lot longer since I moved to rebreather. Usually the loop temperature is about 8 to 10 degree F higher than the water temp. it's not much but enough to keep me warmer longer, my longest dive in 40 degree F. water is 203 minutes, I don't think I could have done the same dive on OC. Oh yeah the cost of gas including Helium for a dive to 300' a big $15.

Al