At cold temperatures the Steadman apparent temperature scale, used to update the present wind chill formulation, offers a replacement for the wind chill formula, tables, and graphs used by the NWS and others. The National Weather Service ( NWS 1992a) employs a version of the Steadman apparent temperature scale as its heat index, using temperature and humidity input only, and assumes appropriate clothing and a very light breeze. Its input variables include air temperature, humidity, wind speed, and external solar radiation loading, and it can be applied to various modeled levels of clothing. The Steadman apparent temperature is operative for both heat stress and cold stress (called wind chill). While similar, the Klima–Michel model was not used in this study. Figure 1 schematically highlights the various heat exchange mechanisms that are representative of the Steadman approach. The Steadman model of heat balance of the human body, originally conceived as a tool for textiles and clothing science, explicitly and implicitly includes all the major heat sources and sinks when estimating heat loss or gain to ascertain the comfort level of a person. Pioneering work by Steadman (1971) and his subsequent refinements (1979a,b, 1984, 19, 1997, unpublished manuscripts) offer an improved wind chill scale based on peer-reviewed research employing a biophysical energy balance model of the human body. Winds above 40 mph are assumed to have no additional chilling effect. The base wind speed at which the wind chill equivalent temperature equals the ambient air temperature is shifted from 0 to 4 mph, which implies that winds less than 5 mph have a warming effect at a given temperature. Furthermore, the traditional wind chill adaptation makes two other assumptions that are not entirely correct. The major consequence is that water, not having a metabolic heat source and not being appropriately attired in human clothing, produces colder wind chills (for given wind and temperature conditions) than those experienced by live, clothed humans. The original wind chill is based on the length of time it took a vessel of near-freezing water to actually freeze under various wind and temperature conditions rather than any human physiological model of heat loss and gain under equivalent conditions. The wind chill concept was pioneered by Siple and Passel (1945), extrapolated for wind speeds above 12 m s −1, and promulgated by the National Oceanic and Atmospheric Administration (NOAA) and the media ( NWS 1992a, b Kuhl 1992). But it may have also made us complacent by exaggerating the chilling effect of the wind at very cold temperatures lulling us, by experience, into the notion that temperatures well below −35☌ (−31☏) are safe, when in fact, they can be dangerous. Unquestionably the current wind chill scale has served us well in highlighting the need for extra clothing and protection in cold, windy conditions. There was a session partly devoted to this topic at the 22d Annual Workshop on Hazards Research and Applications (13–16 July 1997) sponsored by the Natural Hazards Research and Applications Information Center, Boulder, Colorado. Many scientists have noted deficiencies in the current wind chill scale (e.g., Court 1992 Dixon and Prior 1987 Driscoll 1985, 1992, 1994 Kessler 1993, 1994, 1995 Horstmeyer 1994 Osczevski 1995 Schwerdt 1995 Steadman 1995).
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