Winter (daily average temperature is below 0°C) is the longest season in the Barents region. For example in Northern Finland the length of the winter is 150-200 days in a year. The limit of cold work is considered to be +10°C, below which fingers and other body parts susceptible to cold start to cool at light work. Cold environment (low temperature of air) increases heat loss which cools the body. Wind is the worst company of cold air, because the movements of cold air increase efficiently heat loss by carrying away warm air from the skin and clothing and replacing it by cold air. Wind chill index (WCI) describes the combined effect of cold and wind, as shown by the Figure. WCI is divided in the three categories:
• Very cold (WCI -25 ... -35): getting frostbite in uncovered skin is possible during a long stay outdoors
• Risk of frostbite (WCI -35 ... -60): possibility to get frostbite in 10 minutes outdoors
• Great risk of frostbite (WCI more than -60): possibility to get frostbite in two minutes outdoors.
Statistics shows that in the population level the number of frostbite increases sharply when ambient temperature goes below -25ºC.
Figure. Wind chill index (WCI). Please note that the wind velocity is expected to get from weather report. If it is actually measured, you should multiply the velocity by 1.5 before using the table.
Also contact with cold objects, especially metal surfaces, increases greatly the risk of frostbite, because local heat loss can be extremely high in contact cooling.
The cooling of human body depends not only on ambient temperatures but also on clothing (thermal insulation between the skin and environment) and physical activity (producing heat which replaces the heat lost to the environment).
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