The assessment proposal for long-term and short-term tolerable hygrothermal microclimatic conditions

A group of four efficient mine rescuers 25 to 35 years old were exposed to a load of a cyclo-ergometer (stages A and B) and a hand ergometer (stage E) in a climate chamber. The total 120 min period of work was divided into four work intervals, 30 min each. There were 5-min breaks between the individual intervals. The load on the ergometer was selected in the range of 25 to 150 W, Tg=20 to 40 degrees C, rh=40 to 80% and v(a)=0.2 to 1.5 m x s(-1). The thermal resistance of the working suit was 0.65 clo at stage A, 1.07 clo at stage B and 0.81 clo at stage E. A total of 200 experiments with 50 combinations of the work and climate loads were made. The heart rate, oxygen consumption, carbon dioxide production, body temperature, skin temperature, water loss by sweating and perspiration, dry and wet bulb air temperature, air velocity and globe temperature were measured during the experiments. The expected production of sweat (SR) and the amount of accumulated heat in the body (Qmax) were calculated for each combination of the work-climate conditions by a computing program ISO 7933:1989 as well as by our own program. Good agreement was reached between the measured and predicted SR values, calculated by the ISO program (r=0.871) as well as between the values calculated by the two programs, respectively (r=0.985). The experimental results have shown good agreement between the predicted and actually measured values of temperature of the body core as an index of short-term tolerable climate load. The values of short-term tolerable time of work calculated at the level of accumulated heat in the body of 50 W x h x m(-2) resulted in an increase of body core temperature by 0.8 to 1.0 K. The values of heart rate did not mostly exceed 140 beats/min, reaching in exceptional (three) cases values above 150 beats/min. The authors recommend to limit the long-term work-heat (climatic) load during a higher metabolic rate (M >80 W x m(-2) including the basal metabolic rate) of acclimatized males and females at a sweat rate SR=270 g x h(-1) x m(-2), of non-acclimatized persons at SR=206 g x h(-1) x m(-2). The limit for low metabolic rates (M < or = 80 W x m(-2)) for non-acclimatized and acclimatized persons is proposed for long-term tolerable loads of SR=147 g x h(-1) x m(-2). The short-term tolerable load by heat storage within the organism for all categories is proposed as Qmax=50 W x h x m(-2).