INFLUENCE OF INTERMITTENCY AND STATIC COMPONENTS OF WORK ON HEAT-STRESS

This paper summarizes the results of a series of experiments establish ed to examine the effects of the composition and pattern of physical w orkload on human heat tolerance and to compare the predictive abilitie s of a selection of prominent heat stress indices. The experiments wer e carried out in a climatically controlled chamber and involved mixtur es of dynamic (treadmill walking) and static (weight holding) activiti es as appropriate. The average physiological responses to intermittent dynamic workloads did not significantly differ from those to continuo us dynamic work of the same average intensity. However, the average va lues masked periods of peak physiological loading. The inclusion of a static load component had a negligible effect on the average level of physiological thermal strain. As a consequence, the presence or absenc e of a static work component did not influence the predictive abilitie s of the five heat stress indices examined. It was concluded that, whe re peak loading was unlikely to be a problem, time weighted averaging of workload was a reasonable approach in assessing industrial thermal strain and that heat stress criteria, derived originally for continuou s dynamic workloads, were likely to be equally appropriate for intermi ttent combined workloads. However, care should be taken to ensure that peak loading did not present a health risk to industrial populations carrying out intermittent work in hot environments.