Total heat loss as a predictor of physiological response in wildland firefighter gear

In most types of protective clothing heat strain is an important issue. The wildland firefighter clothing system in the USA has seen no major revision over the last decades. In this project the wildland firefighter clothing system was studied at the material and the systems level. On the sweating guarded hot plate and the sweating thermal manikin effects of different base layers (cotton and modacrylic) and meta-aramid outer layers of different fabric weights were evaluated. Then, a human subject trial was performed on a limited set of clothing systems to validate the results from materials and manikin testing. The clothing systems were composed of relevant materials for wildland firefighters with extra configurations added to explore the effects of the highest and lowest levels of protection. All measurement techniques were reverted to a calculation of the total heat loss (THL), as predicted from the hot plate and the manikin and compared to the calculated heat loss from the human subjects. The prediction of the heat strain, based on the sweating guarded hot plate only, gives a large overestimation of the actual heat loss in humans. The currently used standard in the USA that utilizes THL values has no link to actual human heat loss. The manikin showed much better comparison to the human data in absolute terms, but in general underestimated heat loss and showed worse overall correlation to the human heat loss data than the hot plate values.