Human occupational and performance limits under stress: the thermal environment as a prototypical example

The authors wish to challenge the contemporary stress limits for workers exposed to adverse thermal conditions. Further, they wish to challenge the basis upon which all such occupational stress exposures are founded. It is their contention that task performance level should be the primary criterion for exposure. Change in behavioural performance efficiency is the most sensitive reflection of human response to stress. Such responses are superior as indices of incipient damaging effects compared with the traditional measurement of physiological function. Efficient and error-free performance is the principal criterion of contemporary work, especially in high-technology systems. Therefore, continuing exposure after work performance efficiency begins to fail, but before current physiological limits are reached, is inappropriate for both the safety and the productivity of the individual worker, their colleagues, and the systems within which they operate. Behavioural performance assessment should therefore supercede physiological assessment as the primary exposure criterion, although physiological measures still provide important supplementary information. A new description of such performance thresholds for heat stress is presented, together with its substantive theoretical foundation. Performance limits are of growing importance for prescriptions to all forms of occupational exposure and are critical necessities for future statements concerning comprehensive protective safety standards.