Friday, 14 March 2014 11:46

Snow Density For Survival Underneath An Avalanche Important ?

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 How important is snow density for survival underneath an avalanche?

Experimental study conducted with test subjects and an artificial avalanche

2014/03/14, Bolzano, Italy: The snow density may play a much greater role than previously assumed in the ability of a person to survive avalanche burial. Researchers believe that the snow density could exert an even stronger influence than the size of the available air pocket in the snow. In order to investigate this theory, researchers at the EURAC Bolzano, Innsbruck Medical University, the WSL Institute for Snow and Avalanche Research SLF in Davos and the Institute for Sports Science of the University of Innsbruck conducted an experimental study with test subjects and an artificial avalanche in the Puster Valley (South Tyrol) between January and March 2014.

IMG 0720 kleinIn earlier studies, the researchers had observed that a person buried in an avalanche consisting of dry, loosely bonded snow can survive longer than a person engulfed by an avalanche consisting of wet, dense snow, who is likely to be asphyxiated sooner because less air penetrates the snowpack. These observations prompted the question addressed by the recent study: Exactly how great is the influence of snow density on the ability of a person to survive an avalanche burial if he has access to an air pocket in the snow and is able to breathe?

The research team restricted their study to an air pocket having a uniform volume, to a consistent temperature, and to twelve volunteers who underwent testing several times, on each occasion in different snow conditions. For the experiments, the researchers created an artificial avalanche in which they punched out a standardised air pocket for each test subject. The twelve volunteers were members of the mountain rescue teams of the South Tyrol Alpine Club and the Excise Service, and medical students from Austria and Italy. In order to guarantee their safety, the test subjects were not actually buried in the avalanche, but seated closely adjacent to the wall of snow.

For the purpose of investigating the relationship between the survival time and different snow densities, the tests were conducted in three successive cycles in January, February and March 2014.

For the tests, the volunteers breathed directly into the prepared air pocket for 30 minutes. During this 30-minute period the researchers monitored numerous parameters that are relevant to survival, including the oxygen and carbon dioxide content of the volunteers' blood as well as in the air pocket, and the oxygen saturation of the brain, along with other key body functions such as pulse and blood pressure.

In addition, the effort required to breathe in the air pocket was measured at the beginning and end of a 30-minute period. The measured values enabled the researchers to draw conclusions concerning the relationship between the snow density and survival in the event of an avalanche burial. Study project leaders Hermann Brugger and Giacomo Strapazzon of the EURAC Institute for Alpine Emergency Medicine, and Peter Paal of Innsbruck Medical University, described the rationale behind the test method.

IMG 0615 kleinThey said that the tests simulated a complex system, namely the transportation of vital oxygen into the air pocket through snow. The researchers were seeking to establish the relationship between oxygen diffusion into the air pocket and snow density, they explained, because the survival time in snow might be longer than previously assumed. In order to create a control mechanism, volunteers breathed into airtight plastic bags, eliminating the possibility of atmospheric oxygen reaching the air pocket. The control experiment was terminated after two to five minutes because of the lack of oxygen. In contrast, the volunteers breathing in air pockets in loosely bonded snow, having the same capacity, were able to continue breathing easily for 30 minutes. This illustrates the enormous variability of the survival time, depending on the density of the snow surrounding the air pocket.

In relation to the medical data, Jürg Schweizer and his research colleagues at the WSL for Snow and Avalanche Research SLF in Davos analysed the snow density and the properties of the snow surrounding the air pockets used in the tests. They took samples from each of the punched-out air pockets before and after each test, for instance, in order to establish whether the structure of the snow had been altered by the volunteers breathing into the pockets. The researchers also took deep-frozen snow samples of the air pockets back to Davos and analysed the snow structure there in the laboratory by computed tomography (CT). For the first time, moreover, they examined the air permeability of the snow in order to establish how much oxygen can pass through the snow into the air pocket. For this purpose, they extracted air from the air pocket and then measured how quickly the pressure returned from below atmospheric to normal.

The research team are now fairly confident that the snow density could play a greater role than assumed thus far in the ability of a person to survive an avalanche burial. The results of the study are expected to be available within a year. They will be especially useful for estimating the time available for rescuing and attending to people who are buried by avalanches, and for facilitating the development of new safety equipment for ski tourers, freeriders and rescue teams. In conclusion, according to the researchers, the survival curve in the event of an avalanche burial during the six months of winter is probably subject to greater fluctuations than assumed to date depending on the prevailing snow density.


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