Background: Activities using level III personal protective equipment (PPE) in a hot work environment have the potential to cause heat stress which results in discomfort and excessive physiological responses. This study aims to evaluate the occurrence of discomfort and the physiological response profile when doing activities using PPE level III in different working conditions. Methods: The experiment was carried out cross-sectionally and within subject design (repeated measures) in 3 tests (20

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... , 25 ᵒC and 30 ᵒC with relative humidity (50 ± 10) %). Twelve participants with age of (23.7±2.4) years and body mass index of (24.3±3.3) kg/m2 were using PPE level III and carried out a simulation of 6 activities consisting of physical activity, activities requiring concentration and manual dexterity activities for one hour. Microclimate temperature and humidity between skin and clothing, perceived comfort of heat, perceived comfort of wetness, core body temperature, and skin temperature were measured at the end of each activity. The amount of sweat and weight loss were measured after all activities were completed. Result: Working environment temperature (20 ᵒC, 25 ᵒC, and 30 ᵒC) affects microclimate temperature (29.29 ᵒC, 31.70 ᵒC, 33.22 ᵒC, p=0.000), microclimate relative humidity (60.94 %, 92.30 %, 97.31 %, p=0.000), perception of heat discomfort (-0.56, -1.43, -2.04, p=0.000) and perception of wet discomfort (-1.14, -1.57, -2.14, p=0.000), core body temperature (37.45 ᵒC, 37.62 ᵒC, 37.97 ᵒC; p=0.000), skin temperature (35.94 ᵒC, 36.42 ᵒC, 36.85 ᵒC, p=0.000), sweat intensity (41.67 g, 63.67 g, 140.08 g, p=0.023), and weight loss (241.67 g, 291.67 g, 425.00 g, p=0.012). At a working environment temperature of 30 ᵒC, the microclimate reaches a temperature of 33.22 ᵒC and a relative humidity of 97.31 %. This results in high discomfort and a physiological response in the form of a core body temperature that exceeds 38 ᵒC which is an ind [...]