Protection of humans working in open areas during a cold period is of great importance. Cold influences human heat state, health and functional capacity. The assessment criteria for optimal permissible heat state during work time and maximum permissible heat state demanding regulation of cold exposure time are described. They form the basis for estimation and forecast of cold risk. Classification of cooling risk is made on the basis of factors such as mean skin temperature, heat deficit, strain of thermo regulative reactions, thermal sensation, and occupational conditions. Cooling risk is also dependent on human factors such as metabolic rate and clothing thermal insulation and ambient conditions such as air temperature, wind velocity, and exposure time. For evaluation of the cooling risk a regression equation is presented for determination of the integral index of cooling conditions (IICC). On basis of the IICC value, presented in a nomogram it is possible to predict the probability of cooling risk of various rates. In consideration of the shifting climate conditions of Russia, requirements for thermal insulation of protective clothing for four major climate regions of the country are presented.