Application of the relative summary climatic indices during work in heat for ergonomic purposes

Abstract

A new method was elaborated for the evaluation of work-heat load. Two indices of heat stress were introduced, the so called ‘climatic heat’—H_cl (a sum of convective, radiation, respiration and maximum evaporation heat), and the ‘total heat’—H_tot (a sum of metabolic and climatic heat). It is an adapted thermal balance equation in which the evaporation heat was replaced with maximum evaporation heat. This enabled the quantification of climatic load also in the normothermic region, where stored heat S = 0. The applicability of these indices is given by the fact that so called heat heart rate (HR_H) is in good correlation with them (see figure 1 A).

The above mentioned indices were used in the relative values of the ‘quotient of heat stress’ (Q_dif.H) and of the ‘grade of heat strain’ (G_dif.H). These variables are basically a relation between real load and ‘permissible’ load to which a healthy adult male can be exposed for 8 h without an increase in his body temperature. In this paper, equations for calculation of those relative values according to heat stress indices are introduced.

The relative indices show how many times is the real HR_H larger (or smaller) than its permissible value ( = 20 min^-1). By joining the relative heat stress indices with the relative work load indices (Q_{dif, W} and G_{dif, W} respectively) (figure 2) the index of work-heat load is obtained. The permissible work heart rate (= 30 min^-1), which corresponds with the energetic output in males (approximately 250 W).

The work-heat strain grade (G_{dif, WH}) can be used for the quantification of load, for the determination of the rest allowance, of the necessary recovery time and for the determination of a suitable regime of work and rest in general (see nomogram CL-W-TEX, figure 3). With the above nomogram as well as with the nomogram CL-T-RH (figure 4), the permissible values of climatic elements under a given physical load, and the admissible duration of exposure under different climatic conditions and different muscle load intensities can be determined.

Keyword:

• Relative heat stress indices
• Admissible values.