Evaluation of thermal comfort of head gear : a method to measure heat transfer characteristics

Abstract: This study was carried out within the research project "Thermal properties of protective helmets - improvement, validation and standardization of a measurement method" which was a continuation of a research project being carried out since 1992 at the Division of Industrial Ergonomics, Department of Human Work Sciences, Luleå University of Technology, Sweden, with co-operation of the Department of Ergonomics, National Institute for Working, Life (NIWL), Solna, Sweden. A method was developed for measuring the evaporative heat transfer properties of helmets, based on the results of a thorough literature survey. This method has been further improved by building a new sweating head manikin and improving the water (simulated sweat) supply system. Seven different helmets were used in extensive laboratory experiments under various controlled environmental conditions to verify the improvements in the method, and to standardize the measurement procedures. This method was then adapted to measure dry heat transfer properties of helmets. Laboratory tests were conducted with the sweating manikin head under dry conditions (without simulating sweating on the manikin head). The same helmets used in evaporative thermal transfer tests were used in the dry heat loss measurements. Field investigations with human subjects in both hot and cold environments were also carried out to validate the laboratory tests with the method. The results from the laboratory tests showed that the improved method can reveal more detailed information about the evaporative heat transfer from head gear, it is easy to use and control. The field investigation indicated that the subjective results were consistent with the laboratory measurements results in terms of heat transfer. Efforts were made to incorporate the dry heat transfer measurement into the evaporative heat transfer measurement to form a standardized total thermal transfer testing method for head gear thermal evaluations. Further laboratory measurements are proposed to apply this total heat transfer measurement technique to practical tests.