Relationship between heat loss indexes and physiological indicators of turnout-related heat strain in mild and hot environments.

A validated physiological manikin method was used to qualify environmentally dependent correlations between firefighter turnout total heat loss (THL) and intrinsic evaporative resistance ( R _ef ) heat strain indexes and core temperature rise in stressful work conducted in mild (25 °C, 65% relative humidity [RH]) and hot (35 °C, 40% RH; 40 °C, 28% RH) conditions. Five turnout suit constructions representing a wide range of breathability were selected. The observed correlations between measured material heat loss and core temperature showed that the THL heat strain index accurately forecast thermal burden in mild environments (<25 °C); while the R _ef index provided accurate prediction in hot environments (>35 °C). They showed that the THL index did not predict heat strain in hot work environments. The findings of this study support incorporating both the R _ef and THL heat strain indexes as dual metrics for characterizing the heat strain performance of turnout clothing fabrics.