Modified wind chill temperatures determined by a whole body thermoregulation model and human-based facial convective coefficients

Abstract

Wind chill equivalent temperatures (WCETs) were estimated by a modified Fiala’s whole body thermoregulation model of a clothed person. Facial convective heat exchange coefficients applied in the computations concurrently with environmental radiation effects were taken from a recently derived human-based correlation. Apart from these, the analysis followed the methodology used in the derivation of the currently used wind chill charts. WCET values are summarized by the following equation:

$$ \mathrm{WCET}=12.87+0.5334\ast {T}_o-\left(12.66-0.4414\ast {T}_o\right)\ast {U}_{reported}{}^{0.1228} $$

Results indicate consistently lower estimated facial skin temperatures and consequently higher WCETs than those listed in the literature and used by the North American weather services. Calculated dynamic facial skin temperatures were additionally applied in the estimation of probabilities for the occurrence of risks of frostbite. Predicted weather combinations for probabilities of “Practically no risk of frostbite for most people,” for less than 5 % risk at wind speeds above 40 km h⁻¹, were shown to occur at air temperatures above −10 °C compared to the currently published air temperature of −15 °C. At air temperatures below −35 °C, the presently calculated weather combination of 40 km h⁻¹/−35 °C, at which the transition for risks to incur a frostbite in less than 2 min, is less conservative than that published: 60 km h⁻¹/−40 °C. The present results introduce a fundamentally improved scientific basis for estimating facial skin temperatures, wind chill temperatures and risk probabilities for frostbites over those currently practiced.