Whole body heat balance and local insulation required to prevent extremity cooling in extremely cold environments

Introduction
Local cooling in winter conditions is a sensitive and early warning of whole body cooling. Previous studies showed that the equilibrium temperature for the 5th finger is strongly affected by both temperature and insulation. The international standard ISO 11079 is used to calculate clothing insulation required for the whole body based on heat balance equations. However, it does not provide possibility to determine required insulation for local protection. The European standard EN 511 has provided a simple example of the thermal insulation level required as a function of ambient air temperature at a wind speed below 0.5 m/s. The objective of this study was to investigate the relationship between glove insulation and finger temperature in an extremely cold condition.
Methods
Nine subjects participated in a climatic chamber (Ta -30.6 °C, Va 0.4 m/s). Hestra wind stopper fleece fabric gloves and thicker cross country ski mittens (727 g/m2) with micro fleece lining were used for four and five subjects, respectively. Cold protective clothing (Icl=1.89 clo, standard total insulation: 2.26 clo) was used for subjects walking at 232.8 W/m2 to provide whole body thermal comfort according to ASTM F2732.

Results and conclusions
The rectal temperature was relatively stable (37.4 - 37.7 °C) during walking (90 min). The mean little finger temperature reduced to 7.9 (SD 1.4) °C when wearing Hestra wind stopper fleece fabric gloves (0.95 clo), whereas the finger temperature reached 17.8 (1.2) °C when wearing thicker ski mittens (1.46 clo). The insulation of gloves is required to be approximately about the standard total insulation of the ensemble (2.26 clo) to maintain thermal equilibrium of the finger (33 °C). The relationship (Iglove = 0.0522 * Tfinger + 0.5347) between finger temperature (°C) and glove insulation (clo) is established to estimate glove insulation required in this extremely cold environment.