In defensive fighting positions like foxholes or small vehicle crew compartments, movement is very restricted and soldiers must often remain inactive inside them for long periods of time, which can greatly increase the risk of cold injury. Individuals who have experienced a cold injury in the past are at greater risk of experiencing a cold injury than other soldiers. These soldiers may be more sensitive to the effects of cold, or they may not have learned how to properly protect themselves. When the face and other exposed skin areas are covered by camouflage paint, it is difficult to see the changes in skin color which signal the early development of frostbite. For any given air temperature, the potential for body-heat loss, skin cooling, and decreased internal temperature is increased by wind.
Wind increases heat loss from skin exposed to cold air, in effect lowering the temperature.
The wind-chill index integrates windspeed and air temperature to provide an estimate of the cooling power of the environment and the associated risk of cold injury. Appendix A depicts the Equivalent Chill Temperature for different wind speeds and air temperatures. To find the equivalent chill temperature in the table, find the row corresponding to the windspeed, and read across until reaching the column corresponding to the air temperature. When assessing weather conditions for troops operating in mountainous regions or for flight personnel in aircraft, altitude may need to be considered, if weather measurements are obtained from stations at low elevations. Temperatures, windchills and the risk of cold injury at high altitudes can differ considerably from those at low elevations.