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

Satoru Ueno

doi:10.1186/s40101-020-00235-9

Abstract

BackgroundThermal 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 (CFi) and evaporative resistance (CFe), respectively. Then, CFi and CFe 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 CFi and CFe 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.MethodsCFi of ISO 7933 (CFi7933) and ISO 9920 (CFi9920), and CFe of ISO 7933 (CFe7933) and two kinds of CFe of ISO 9920 (CFe9920a, CFe9920b) 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 CFi9920 and CFe9920a (PHSmA) and modified PHS integrated with CFi9920 and CFe9920b (PHSmB). We calculated the rectal temperature, water loss, and exposure time limit by PHS, PHSmA, and PHSmB and compared the results.ResultsCFi7933 and CFi9920 were almost similar in terms of Var and walking speed, while CFe9920a and CFe9920b were larger than CFe7933 when Var was more than 1.0 m·s−1. Intrinsic clothing insulation (Icl) diminished the effects of Var on CFi7933, CFi9920, CFe7933, and CFe9920b. However, CFe9920a was not influenced by Icl. The predicted rectal temperature and water loss difference were larger between PHS and PHSmA as CFe difference got larger. The duration time when limit of rectal temperature of 38 °C was reached (DlimTre38) calculated by PHS was significantly longer than PHSmA, PHSmB at higher Var.ConclusionsPrecise correction factors for evaporative resistance are required to predict rectal temperature, water loss, and work-time limits.

Highlights

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
CFi of International Organization for Standardization (ISO) 7933 (CFi7933) and CFi of ISO 9920 (CFi9920) did not differ in nude, the clothing thermal insulation of 0.3 clo and more than 0.6 clo in terms of walking speed (Fig. 1b)
CFe of ISO 7933 (CFe7933) was smaller than CFe9920a and CFe9920b in both for relative air velocity and walking speed

Summary

Introduction

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. Clothing decreases heat transfer between the human body and the environment through convection, conduction, radiation, and evaporation. A wearer’s activity increases heat transfer by the exchange of air between the inside of the clothing and the environment by “pumping effects” [8] through openings in the clothing. Increased vapor transfer to the environment decreases the microenvironmental humidity inside the clothing, which promotes evaporation on wetted skin, leading to increased heat transfer between the body and the environment. When heat loss by sweating is suppressed by vapor-impermeable clothing, though it serves to protect the human body from hazardous materials, thermal physiological strain increases [10,11,12]

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