Comparison of correction factor for both dynamic total thermal insulation and evaporative resistance between ISO 7933 and ISO 9920

BACKGROUND: Thermal insulation and evaporative resistance of clothing are the physical parameters to quantify heat transfer and evaporative dissipation from the human body to the environment, respectively. Wind and body movement decrease thermal insulation and evaporative resistance of clothing, which is represented as correction factors for dynamic total thermal insulation (CF(i)) and evaporative resistance (CF(e)), respectively. Then, CF(i) and CF(e) are parts of the key parameters to predict heat strain of workers by computer simulation. The objective of this study was to elucidate the difference of CF(i) and CF(e) between ISO 7933 and ISO 9920 and compare the difference of predicted rectal temperature, water loss, and exposure time limit calculated by using each correction factor. METHODS: CF(i) of ISO 7933 (CF(i7933)) and ISO 9920 (CF(i9920)), and CF(e) of ISO 7933 (CF(e7933)) and two kinds of CF(e) of ISO 9920 (CF(e9920a), CF(e9920b)) were compared in terms of relative air velocity, walking speed for three kinds of thermal insulation of clothing. Next, two modified predicted heat strain (PHS) models were developed: modified PHS integrated with CF(i9920) and CF(e9920a) (PHS(mA)) and modified PHS integrated with CF(i9920) and CF(e9920b) (PHS(mB)). We calculated the rectal temperature, water loss, and exposure time limit by PHS, PHS(mA), and PHS(mB) and compared the results. RESULTS: CF(i7933) and CF(i9920) were almost similar in terms of V(ar) and walking speed, while CF(e9920a) and CF(e9920b) were larger than CF(e7933) when V(ar) was more than 1.0 m·s(−1). Intrinsic clothing insulation (I(cl)) diminished the effects of V(ar) on CF(i7933), CF(i9920), CF(e7933), and CF(e9920b). However, CF(e9920a) was not influenced by I(cl). The predicted rectal temperature and water loss difference were larger between PHS and PHS(mA) as CF(e) difference got larger. The duration time when limit of rectal temperature of 38 °C was reached (D(limTre38)) calculated by PHS was significantly longer than PHS(mA), PHS(mB) at higher V(ar). CONCLUSIONS: Precise correction factors for evaporative resistance are required to predict rectal temperature, water loss, and work-time limits.