Heat balance model for a human body in the form of wet bulb globe temperature indices

• Published in: Journal of thermal biology Vol. 71; pp. 1 - 9
• Main Authors: Sakoi, Tomonori, Mochida, Tohru, Kurazumi, Yoshihito, Kuwabara, Kohei, Horiba, Yosuke, Sawada, Shin-ichi
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2018; Elsevier BV
• Subjects: Adjustment factor; Body temperature; Heat balance; Heat stress; Heatstroke; Protective clothing; Radiation; Skin; Solar radiation; Temperature; Temperature effects; Thermal environment; Vapors; Wet bulb globe temperature; Adjustment factor; Wet bulb globe temperature; Heat stress; Solar radiation; Clothing; Thermal environment
• ISSN: 0306-4565; 1879-0992
• DOI: 10.1016/j.jtherbio.2017.10.002

The purpose of this study is to expand the empirically derived wet bulb globe temperature (WBGT) index to a rational thermal index based on the heat balance for a human body. We derive the heat balance model in the same form as the WBGT for a human engaged in moderate intensity work with a metabolic heat production of 174W/m2 while wearing typical vapor-permeable clothing under shady and sunny conditions. Two important relationships are revealed based on this derivation: (1) the natural wet bulb and black globe temperature coefficients in the WBGT coincide with the heat balance equation for a human body with a fixed skin wettedness of approximately 0.45 at a fixed skin temperature; and (2) the WBGT can be interpreted as the environmental potential to increase skin temperature rather than the heat storage rate of a human body. We propose an adjustment factor calculation method that supports the application of WBGT for humans dressed in various clothing types and working under various air velocity conditions. Concurrently, we note difficulties in adjusting the WBGT by using a single factor for humans wearing vapor-impermeable protective clothing. The WBGT for shady conditions does not need adjustment depending on the positive radiant field (i.e., when a radiant heat source exists), whereas that for the sunny condition requires adjustments because it underestimates heat stress, which may result in insufficient human protection measures. •We obtained a human body heat balance models with the same form as the WBGT.•The derived model agreed with WBGT at a skin wettedness of 0.45.•WBGT was regarded as amount of skin temperature change rather than heat storage rate.•Adjustment factor for WBGT was available from values used in heat balance equation.•WBGT needs to be adjusted according to radiation excluding the effect of sunshine.