cold environment, a human environment arbitrarily designated as one in which the temperature is below 10° C (50° F). Nearly two thirds of the world population, including most of North America, Europe, and Asia north of the Indian subcontinent, live in a naturally cold environment for at least a part of each year. The human body generally begins to experience some functional impairment when unprotected in temperatures below 15° C (59° F). The hands and fingers lose sensitivity, and the risk of errors and accidents increases. The body’s hemostatic mechanism reacts with vasoconstriction, reducing heat loss to the environment but cooling the skin with a resultant chilling of the extremities. When vasoconstriction no longer eases the thermal strain between the skin and the environment, muscular hypertonus and shivering become mechanisms for maintaining body temperature.
