Comparison of weather service heat indices using a thermal model

The US and Canadian weather service heat indices were evaluated to determine if one is a better predictor of the risk of heat injury. Heat index values were compared to the rectal temperature predicted by a heat-balanced-based thermal model to determine if there was a statistically significant relation between the heat index values and predicted rectal temperature. R2 values ranged between 0.96 and 0.99 for the conditions investigated. Equations that predicted rectal temperature from the heat indices are presented. Both indices are highly correlated with predicted rectal temperatures.