A natural and important starting point to practical assessment is to consider human response to thermal environments as being determined by the air temperature, radiant temperature, humidity and air velocity in which the people work as well as their activity and the clothing that they wear. The opportunity afforded to them by the environment to reduce their exposure to cold stress is also of importance (e.g. rest in a warmer area and increase clothing levels). A primary consideration when conducting a practical assessment of a cold environment is to determine where, when and what to measure. It is of great importance to determine at the outset, exactly what the aim of the survey will be and what will be delivered. Mean radiant temperature is the temperature of a uniform enclosure with which a small black sphere at the test point would have the same radiation exchange as it would have with the ‘actual’ environment.