Appropriateness of international heat stress standards for use in tropical agricultural environments.

Where a danger to health from heat stress is identified, standards allow decisions for implementing measures to reduce the heat stress to be made. These standards, specifically ISO 7243 (Wet Bulb Globe Temperature Index, WBGT) and ISO 7933 (Sweat Required, SWreq) were designed with European and American subjects, primarily for use in those countries. While the scope of the standards is international, little consideration has been made about how valid and usable they are in industrially developing countries. This investigation evaluated ISO 7933 and ISO 7243 in terms of validity and usability. A tropical agricultural task was simulated; 16 subjects plucking tea leaves for 2 h, (ta = tr = 37.18 degrees C; va = 0.16 m/s; rh = 70.17%). While ISO 7243 was valid (if slightly over protective) and usable, ISO 7933 was over protective and underestimated sweat and evaporation rates in its predictions. The discrepancies between predicted and observed results were attributed primarily to the calculations related to clothing in the standard. Furthermore, ISO 7933 was unusable without a computer; in regions where access to such technology may be limited, a simpler method of presentation is required.