Guidelines on risk of frostbite
New wind chill research has determined precisely how long it takes for exposed skin to freeze in cold winter weather. A team of scientists and medical experts tested volunteers in a refrigerated wind tunnel to gauge their response to high winds and freezing temperatures. This work, which was carried out by Defence Research and Development Canada - Toronto in the spring of 2003, has enabled scientists to develop new frostbite guidelines to help safeguard the military, and, ultimately, all Canadians.
This new research builds on earlier work which was used to revamp Environment Canada's wind chill index in 2001. Wind chill is the cooling sensation caused by the combined effect of temperature and wind. It can cause cold-related injuries like frostbite and hypothermia. The first volunteer studies, carried out in 2001, enabled researchers to develop a general understanding of how the human body responds to wind chill. The new research provides more precise information on the level of risk and the time it takes for exposed skin to freeze.
Volunteers, wearing winter clothing with only their faces exposed, sat in the wind tunnel for up to 45 minutes at a time. They were exposed to various temperatures and wind speeds, with researchers closely monitoring their condition. The volunteers were removed from the wind tunnel when they developed frostnip - a condition where the skin turns white, but only the very superficial outer layer has frozen. If the skin is immediately heated, for example, with a warm hand, this condition can be reversed and the skin is not harmed. Researchers estimate that frostbite, where the skin and underlying layers of tissue freeze, will develop within 30 seconds to one minute after the first signs of frostnip. Using this method, the research team was able to clearly define the level of risk and to provide very precise information on the time it takes for exposed skin to freeze under various wind and temperature conditions.
Researchers found a very clear cutoff point in the tolerance of human skin to cold. For wind chill index values from zero down to -27, most of the volunteers did not develop frostnip during the 45 minute trial. However, once the wind chill was colder than -27, the risk increased rapidly. At -40, all the volunteers developed frostnip within ten minutes, and at -55, all developed frostnip within two minutes. Since the volunteers had been chosen to represent a range of healthy adults, the researchers were able to use this study to develop frostbite guidelines which would apply to most healthy Canadian adults.
Environment Canada is now integrating these results into its wind chill index program, to provide more accurate information to help safeguard the health of Canadians during cold winter weather.
For more information, please consult the various charts and tables on this site.
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