Thermal performance trials on the habitability of private bushfire shelters: part 2
In the preceding communication, an investigation was described in which the thermal specifications for the design of private bushfire shelters were evaluated. Since those trials were undertaken with the thermal characteristics of the air clamped, survival uncertainty persisted if the internal ambient conditions were progressively changing, as would occur within an air-tight shelter. Therefore, two further investigations were performed. In the first, changes in the physical properties of air within an air-tight shelter simulator (1.2 m3), initially equilibrated to 43.7 °C and 42.3 % relative humidity, were studied when pre-heated, well-hydrated males were sealed inside (N = 16; 60 min; experimental series 2). Air temperature and humidity moved sigmoidally to 40.5 °C (standard deviation (SD), 0.5) and 90.1 % (SD, 2.1). Oxygen and carbon dioxide fractional concentrations changed reciprocally, with respective terminal averages of 16.7 % (SD, 0.8) and 3.94 % (SD, 0.72). Deep-body temperature rose beyond the tenth minute to a terminal mean of 39.3 °C (SD, 0.2). In the third experimental series, these air temperature and humidity changes were reproduced in trials commencing at two different thermal states (40 °C and 70 % relative humidity; 45 °C and 50 % relative humidity). Sixteen pre-heated and slightly dehydrated men and women were investigated. In neither condition did the auditory canal temperature of any individual change by more than 2 °C or exceed 40 °C. It may be concluded, within the limits of these experiments, that the recommended thermal and dimensional specifications for bushfire shelters can provide tenable conditions for healthy, young adults.