Testing climate indices in the field

To validate the climate index ‘required sweat rate’ (ISO/DIS 7933, 1986), in a common research action of the ECSC, several European working parties performed field tests and analysed the data on stress and strain at the workplace. Field tests, covering most distinct conditions of work and climate, should be used to validate climate indices, because a standard has to prevent health damage under real working conditions. The time variation of muscular work and heat load requires the consideration of the pre-history of load, in order to examine the effects on more delayed physiological strain. A method using an exponentially weighted floating mean value with a time constant of 10 min was found to be suitable. The ‘required sweat rate’ index provides a better description of the measured sweat rate than do the other indices based on the sweat rate (ITS, P4SR). This applies to the prediction of averages and exposure limits, as well as to the regression gradient. Laboratory tests are used to improve the model, concerning the mean skin temperature and the evaporative efficiency of sweating. The limitation of exposure given by the evaluation of the required sweat rate is ‘on the safe side’, if these modifications are used in conjunction with the criteria of the ‘warning’ level. The indices ‘required sweat rate’ and WBGT, on which are based ISO standards 7933 and 7243, provide virtually identical results for the limits of an 8-hour exposure.