LAUSR

The wet-bulb temperature of 35 °C has been widely used as the threshold for human survivability in the field of climate science. However, recent experiments have shown that a person's core temperature starts to rise at a range of critical wet-bulb temperatures well below this threshold. It is shown here why this state of severe heat stress cannot be predicted using the wet-bulb temperature. Instead, it is shown that the recently extended heat index can explain nearly all of the variance in the observed critical combinations of temperature and humidity in those heat-stress experiments. For light and moderate exertion in an indoor setting, the heat index predicts that the critical wet-bulb temperature ranges from 20 to 32 °C, depending on the relative humidity, consistent with experimental results. For the same setting and exertion, the heat index predicts fatal wet-bulb temperatures ranging from 24 to 37 °C. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.