EVAPORATIVE HEAT-TRANSFER CHARACTERISTICS OF INDUSTRIAL SAFETY HELMETS

Thermal discomfort is one of the major complaints from the wearers of industrial safety helmets. While studies have been reported on dry hea t transfer (conduction, convection and radiation) in safety helmets, t he investigation of wet heat dissipating (evaporation) properties has not been found in the literature. To evaluate experimentally the evapo rative heat transfer characteristics of industrial safety helmets, a m ethod was developed to simulate sweating of a human head on a thermal head manikin, and to use this manikin to assess the wet heat transfer of five industrial safety helmets. A thermal head manikin was covered with a form-fitting cotton stocking to simulate 'skin'. The skin was w etted with distilled water to simulate 'sweating'. A form-fitting perf orated polyethylene film was used to cover the wetted stocking to cont rol the skin wettedness at two levels, 0.64 and 1.0. Experiments were conducted in a climatic chamber, under the following conditions: the a mbient temperature = head manikin surface temperature = 34 +/- 0.5-deg rees-C; ambient relative humidity 30% and 60%. Also, the effects of wi nd and a simulated solar heat load were investigated. The five helmets showed statistically significant difference in evaporative heat trans fer under the experimental conditions. Skin wettedness, ambient humidi ty, wind and solar heat showed significant effects on evaporative heat transfer. These effects were different for the different helmets.