Characteristics and Consideration of Required Sweat Rate Standard of the Previous ISO 7933

Abstract

It is important to understand the applicable conditions and characteristics of thermal indices for their proper application. In this paper, the characteristics of the required sweat rate of the previous ISO 7933 standard are investigated from the viewpoints of the thermal physiology and thermal equilibrium of the human body. A linear multiple regression formula used for the prediction of skin temperatures is not always consistent with the relation between the thermal physiological states and sweat secretion in the human body. With the decrease in the sweat efficiency brought about by hot and humid conditions, an error in the evaluation of skin temperature leads to a larger error in operative temperature according to the previous ISO 7933. In order to compensate for this error, this paper suggests that both the skin temperature and sweat rate should be evaluated based on the thermal equilibrium of the human body and the relationship between the thermoregulatory system and thermal physiological states. In order to create a new hot environmental index based on the previous ISO 7933 standard, which uses heat storage and dehydration as parameters for evaluation, the authors present an example of such evaluation methods. In this example, sweat secretion corresponds with the rise in skin temperature.