n Southern African Forestry Journal - Evaluation of methods for estimating the metabolic rate according to ISO 8996 in forestry work in Zimbabwe : scientific paper




Forestry activities in Southern Africa may expose forest workers to uncompensable heat stress risk when the climate conditions are such that the body experiences difficulties to dissipate its excess heat to the environment. A study was made in North Eastern Zimbabwe during the hot season to evaluate ISO standard methods for heat stress risk determination in manual forestry work. The differences between the metabolic rate assessments by three methods of ISO 8996 were evaluated, as well as the effects of these variations in the assessments on the heat stress risk determination by ISO 7243 and 7933. The results showed significant differences between the metabolic rate assessment methods, with variations of up to 36% for the same observation period. It was also found that the methods responded inconsistently for different activities. ISO 7243 and 7933 gave contradictory assessments of the heat stress risk in the prevailing climate conditions and the differences in the recommended allowable exposure times by ISO 7933 were up to 265 minutes. It is therefore questionable whether the ISO heat stress standard methods in their present versions are applicable to all work situations in forestry.


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