Myth Buster: Argon, the Superior Dry Suit Inflation Gas?
Staying warm during the dive is not just a matter of comfort. As we have learned from the 2007 NEDU study, it also affects our decompression and, subsequently, our DCS risk. Supplemental insulation provided by dry and wet suits will shift the Lower Critical Temperature (which is the ambient temperature at which heat production responses are initiated) to lower values and thus, delays the onset of core cooling as water temperature decreases. Diving ‘dry’ will allow for much wider manipulation of thermal insulation with the use of differing undergarments that have their own thermal insulation properties.
It is common belief that additional insulation can be acquired by choosing the proper gas for dry suit inflation. Over the years there have been lively discussions and a lot of theorizing over what dry suit gas is best. Helium is considered undesirable. Less so because of cost, but more so because of its theorized thermal properties and issues with isobaric counter diffusion. Some strongly believe that Argon is the best gas. It’s molecular weight of 39.948 make it heavy compared to Air (28.966). It is also a denser gas, 1.784 g/l, than Air at 1.225 g/L. These properties have been used to argue for Argon being ‘warmer’ and thus superior to Air for dry suit inflation.
Particularly important in the commercial sector, protecting the diver from cold and its effects fueled the research in thermal considerations when diving. The Clo is a unit of measurement used to describe insulation afforded by clothing. It is also used to describe thermal properties in gases. Take a look at the chart below (from Lippitt & Nuckols 1983) which gives relative insulation values for dry suit inflation gases.
Discounting CO2 and SF6, Argon appears superior in thermal insulation properties. Theoretically, it should be almost 32% more effective in thermal insulation than Air. However, a 2001 study by Risberg & Hope failed to prove Argon’s superiority. Replacing Air with Argon had no effect on skin and core temperature, as well as, on the perception of thermal comfort. In this experiment, divers where held in a prone (face down) position at 33 ft (10 m) for 1 h in water with a mean temperature of 2 C. The region that received some benefit (although very small) was in the back. A plausible explanation to this observation is from the exertion of hydrostatic pressure causing a shifting of gas. Because the divers where in a prone position, the water’s hydrostatic pressure displaced most of the gas to the back, thus accounting for the decrease in heat loss primarily from that site.
As a final note: despite dry suits being superior in thermal insulation compared to wet suits, they are not without limits and inadequate for long duration deep dives, particularly in cold waters. This is why saturation divers working in cold environments require active heating by hot water suits which are superior to electrically heated suits.
So what does this mean to you? It appears that Argon does not offer any advantages over Air for dry suit inflation. Given that it does not appear to insulate any better, it is actually more expensive, more difficult to procure, and unbreathable. The Risberg and Hope study is clearly another myth buster to a commonly held and passionately debated misconception. What appears logical does not always translate into what is true when applied.
This article has created an interesting dialogue. As a result, a 2008 study* was brought to our attention, where it was reviewed, and now considered in our thoughts. What follows is an update to the original article:
Like with so many experiments that have the same topic of study, there are various differences.
Here, in the 2008 study by Nuckols, Giblo and Wood-Putnam, they purged the dry suit six times. There was no mention in the 2001 study by Risberg and Hope, of whether they purged the suit multiple times or at all. As suggested by Nuckols, Giblo and Wood-Putnam, that might have important implications.
The other important difference is the manikin’s position during the experiment. From the pictures, it looks like it was kept sitting up. If Risberg and Hope were correct in their assumption that hydrostatic displacement of gas plays a role, then the Nuckols, Giblo and Wood-Putnam study might reflect that in their data, as well, but to a point (i.e. legs had the least benefit from Argon). The outcome data might be a bit different if the mannequin was kept prone.
The real test would be to have a study that tests both elements:
Purge dry suit at least 6 times with Argon
Keep divers or mannequins in a prone (swimming) position during the experiment
If done with humans, include the subjective perception during the blinded experiment
So all this leads me to believe that the jury is still out! We have two studies with conflicting results. The main point remains that the type of undergarment one wears appears to make the biggest difference and that active heating is most important in very cold and long exposure dives.
Claudia Sotis MD
Lippit MW, Nuckols ML – Active diver thermal protection requirements for cold water diving
Aviat Space Environ Med 1983; 54: 644-648
Risberg J, Hope A – Thermal insulation properties of argon used as a dry suit inflation gas
Undersea Hyperb Med 2001; 28: 137-143
Brubakk AO, Neuman TS – Bennett and Elliott’s Physiology and Medicine of Diving – 5th Edition
Saunders Elsevier 2003
*Nuckols ML, Giblo J, Wood-Putnam JL
Thermal Characteristics of Diving Garments When
Using Argon as a Suit Inflation Gas
Duke University, Durham, North Carolina, 27708