Air or Argon in Dry Suit Inflation Cylinder?

[terrillja]

Originally posted on the deco stop

DOES ARGON IMPROVE DIVER COMFORT AND WARMTH WHEN COMPARED TO AIR AS A DRY SUIT INFLATION GAS?

In this article we present the first in a series of topical scientific paper reviews written by members of the Undersea and Hyperbaric Medical Society Diving Committee. This series will continue as more reviews are generated.

This issue’s article is of particular relevance to technical divers who frequently carry an extra cylinder of argon for drysuit inflation purposes.

PAPER TITLE:

Thermal insulation properties of argon used as a dry suit inflation gas.

AUTHORS:

J Risberg, A Hope.

REVIEWER:

Simon Mitchell.

REFERENCE:

Undersea and Hyperbaric Medicine 2001;28(3):137-143

THE PURPOSE AND AIMS OF THE STUDY:

Diving is frequently conducted in very cold water and it is recognised that under these circumstances a dry suit will provide superior insulation than a wet suit. A dry suit traps a layer of gas between the diver and the water and since gas is a less efficient conductor of heat, this means that there is less direct conduction of heat from the diver to the environment.

Based on the known physical properties of various gases, it might be predicted that some will be better than others when used to “insulate” a diver in a dry suit. For example, argon has a specific heat capacity (the amount of energy required to raise the temperature of a defined quantity by 1 degree) and a thermal conductivity (the rate of heat energy transfer through a small volume of the gas given a standard temperature gradient on either side) that is about 30% less than air in both cases. This would suggest that argon would provide better insulation for a diver in a dry suit.

Some divers, particularly technical divers, go to the trouble of carrying a separate cylinder of argon for use as a dry suit inflation gas, and most believe that argon makes them feel warmer in comparison to air. However, as the authors of this paper point out, this contention had not been evaluated objectively. The reason it is important to do this is that there is a vast potential for a “placebo effect” where parameters like perceived warmth are being subjectively judged. Put another way, if a diver is told that a particular dry suit inflation gas will make them feel warmer, there is potential for the “power of suggestion” to influence their judgement. Thus, in this study, the authors set out to eliminate any placebo effect by running dives in which the divers did not know what dry suit inflation gas was being used when they made judgements about thermal comfort. They also used electronic thermistors to accurately measure actual temperatures rather than relying on the divers opinions alone.

THE METHODS:

The authors recruited 6 Norwegian Navy divers who dived using Poseidon Unisuit drysuits and “woolly bear” undergarments. Prior to “dressing into” their undergarments and suits, the divers were “instrumented” with thermistors (temperature measuring probes) at multiple skin sites (including the chest and back) and in the rectum (as a measure of central or “core” temperature).

Each diver completed 2 dives (separated by 24 hours) to 10m for 60 minutes in water at 2 degrees Celsius. The divers rested during the dives. The dry suit inflation gas was argon on one dive and air on the other, but neither the divers nor the experimenters knew the order until both dives were complete and the data recorded. A standardised suit flushing procedure was developed to ensure that the suit was thoroughly flushed with the gas of interest on each dive.

During the dives, the temperature at the various thermistors was constantly recorded, and the divers were asked to subjectively rate their thermal comfort (eg very warm, warm, comfortable, cold, very cold etc).

THE RESULTS:

The temperature decreased during the course of the dive at all points where thermistors were applied (including the rectum), but there was no difference in the magnitude of the drop between the dives with argon or air as the dry suit inflation gas. Nor was there any difference in the divers’ opinions of their warmth between the air and argon dives. Interestingly, there was a statistically significant difference between the magnitude of skin temperature drop on the back and chest in both air and argon dives (on average, chest fell by about 4 degrees more).

WHAT DOES ALL THIS MEAN?

In this group of divers with the particular equipment configuration employed, and under the fairly extreme environmental conditions that prevailed, the use of argon as a dry suit inflation gas did not appear to confer any advantage in terms of thermal protection.

However, one needs to be careful about drawing the conclusion that argon is not useful as a dry suit inflation gas in any situation. As is usual in good scientific papers the authors are careful to identify any potential weaknesses in their results. They point out that a resting dive (as conducted here) would be unusual in either a naval operational setting or a technical dive, but this is mitigated by the fact that a resting dive (as opposed to a working dive) is most likely to result in a significant temperature drop, and therefore most likely to identify any potential advantage for argon. They also point out that their population of divers and the number of dives was small. From a statistical point of view, this might mean that there were an insufficient number of trials to reveal a significant difference between argon and air dives, particularly with respect to the subjective opinions of the divers. However, this is also mitigated by the widely and strongly expressed subjective opinion that argon is clearly superior. The authors argue that were this truly so, some indication of the effect should have been apparent even in their relatively small experiment.

So, notwithstanding the potential weaknesses of the study outlined above, one conclusion that might be drawn is that despite its theoretical attraction, argon in the dry suit simply doesn’t make a big difference at a practical level. This might be because there are too many sources of heat loss that argon in the dry suit cannot modify. These sources would include the hands, face, and heat loss from the respiratory tract and those dependent areas (such as the chest in the horizontal position) where the dry suit and undergarment are squashed hard against the diver thus minimizing any thermal advantage of the inflation gas.

There remains the question as to how there could be such a glaring difference between the popular opinion that argon is superior and what this study has shown. The authors speculate that one explanation for a misperception of superiority is that individual divers’ personal experiences are not based on blinded evaluation and are therefore subject to a placebo effect (as described earlier).

THE BOTTOM LINE

On the one hand we have a popular opinion that argon is highly effective adjunct to thermal protection in dry suits, but this opinion is potentially subject to a very strong placebo bias. On the other hand we have a scientific study that demonstrates no large advantage for argon, but this study may have been too small to reveal a more subtle benefit. The truth about argon as a dry suit inflation gas may lie somewhere between these two extremes, but the benefit is unlikely to be substantial. Divers will have to draw their own conclusions about the merits of extra cylinders of argon with their associated cost and inconvenience in the light of these findings.

[terrillja]

I'd like to see them do this with an He mixture, and see what the results are.

[Lake Diver]

You'd float up above the surface of the water with HE in your suit!

[Chad]

And freeze.

[terrillja]

Originally Posted by Chad

And freeze.

Well I want to see the numbers, if the temperature drop is 12 degrees, that's a lot more than air, if it's just 5, not a huge difference. I'd just like to see the numerical data to back up what divers have been saying for a while.

[texdiveguy]

In my experience diving a ds inflation system and having used both AIR and ARGON on different occasions I don't find much thermal chance in terms of my comfort level. I have read reports generated by several groups looking at this very topic and there is no major evidence supporting much of a difference. For the most part I use AIR for its ease of availability at fill stations and as a cost factor.

[CompuDude]

This is the same test that keeps getting trotted out. There really needs to be a new study done with more current protocols. (and more current undergarments) There are a bunch of other issues with it that I've read, but can't recall off the top of my head.

The other thing to consider is this tested argon against air. Fair enough, but it doesn't really address the fact that you REALLY need some sort of redundant DS inflation system (be it air or argon) if you're diving helium mixes in your back gas. I've seen it used to support that theory, is the only reason I mention this.

[ChrisA]

These guys went to a lot of trouble for nothing. No one use argon because it is so much btter than air, they use argon because it is so much better than helium. Tech divers cary argon because (1) their tri-mix is not the best gas for the drysuit and (2) you have to cary _something_ so why not argon?

[texdiveguy]

There is no reason why someone diving trimix would want to use such for a ds inflation medium. Its costly,,a very poor thermal insulator and can contribute to 'skin bends'.....for these are 3 reasons you will see mix divers using either AIR or ARGON delivered via an inflation system to the ds.