South-Eastern Australia experiences the most frequent and severe bushfires in the world. In 2009, bushfires in Victoria claimed 173 lives and cost more than $4 billion in structural damage. As a consequence, the establishment of building standards that might govern the construction of bushfire shelters was recommended. Since no relevant standards existed, it was suggested that if these shelters could keep the internal conditions to a maximal mean Modified Discomfort Index (MDI) of 39o for 60 min, then they could restrain the rise in core temperature to no more than 2oC. The current investigators were invited to test this hypothesis and, in this communication, provide a physiological evaluation of this recommendation across two experiments. In the first experiment, the aim was to evaluate the physiological impact of a 10oC variation in air temperature that could be encountered at a constant Modified Discomfort Index of 39o. The objective of the second experiment was to explore changes within the internal environment of an air-tight shelter containing pre-heated and sweating occupants.