Windchill And Its Effects
At any temperature, you feel colder as the wind speed increases. The combined effect of cold air and wind speed is expressed simply as the “wind chill” temperature in degrees Celsius or Fahrenheit. It is essentially the air temperature that would feel the same on exposed human flesh as the given combination of air temperature and wind speed. It can be used as a general guideline for deciding clothing requirements and the possible health effects of cold. If your workplace experiences any sort of windchill, then maybe it’s time to ditch your best rated cooling towel that you used to use at work.
A surface loses heat through conduction, evaporation, convection, and radiation. The rate of convection depends on both the difference in temperature between the surface and the environment surrounding it and the velocity of the air with respect to the surface. As convection from a warm surface heats the air around it, an insulating boundary layer of warm air forms against the surface. Fast-moving air disrupts this boundary layer, or epiclimate, allowing for cooler air to replace the warm air against the surface. The faster the wind speed, the more readily the surface cools.
In the US, the term “wind chill” or “wind chill index” is used. This factor is a measurement of a heat loss rate caused by exposure to wind and is expressed in temperature-like units.
Environment and Climate Change Canada have produced a Wind Chill Temperature Index and guides to help estimate wind chill and wind speed.
NOTE: Environment and Climate Change Canada’s recommendations consider all individuals who may be outside, including young children and the elderly. These recommendations may not match exposure values developed by other organizations that have specifically made recommendations for working adults who are in good general health.
For working populations, the American Conference of Governmental Industrial Hygienists (ACGIH) also provides recommendations. These recommendations were developed to protect workers from the severest effects of cold stress (hypothermia and frostbite). The recommendations also describe exposures to cold working conditions under which it is believed nearly all workers can be repeatedly exposed without adverse health effects. Included in these recommendations is the following wind chill temperature index.
How Did Windchill Become So Popular?
The core idea behind wind chill was first developed in the 1940s by Paul Siple and Charles Passel, a pair of American scientists working in Antarctica. It was long known that wind caused objects to lose heat more quickly, by blowing away the layer of warmer air that surrounds them. Siple and Passel tried to measure this effect by studying the freezing rates of water bottles placed on top of their hut in Antarctica.
These calculations helped them develop what they called the “wind chill factor.” For years, this metric was used mainly by scientists, because Siple and Passel expressed it in units of kilocalories per hour per square meter — a technical measurement of heat loss that was lost to most people.