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A Proposal for the Assessment of Long-Term and Short-Term Tolerable Hygrothermal Microclimatic Conditions

Technical University of Prague

Z. Jirák

Hygiene Institute, Ostrava, Czech Republic

H. Jiráková

Hygiene Institute, Ostrava, Czech Republic

P. Bajgar

Hygiene Institute, Ostrava, Czech Republic

A group of four experienced mine rescuers, aged 25-35 years, were exposed to a workload on both a cyclo-ergometer (stages A and B) and a hand ergometer (stage E) in a climate chamber for work periods of 120 min divided into four intervals of 30 min each with 5 min breaks between. The load at the ergometer was selected to be in the range of 25-150 W, T_g = 20-40°C, RH = 40-80% and V_a = 0.2-1.5 m.s^-1. The thermal resistance of the clothes worn was 0.65 clo in stage A, 1.07 clo in stage B and 0.81 clo in stage E. A total of 200 experiments with 50 combinations of the work and climate load were made. Heart rate, oxygen consumption, carbon dioxide production, body temperature, skin tem perature, water loss by sweating and perspiration, dry and wet bulb air temper ature, air velocity and globe temperature were measured during the experi ments. The expected production of sweat (sweat rate; SR) and the amount of accumulated heat in the body (Qmax) were calculated for each combination of the work-climate conditions. The experimental results showed a good agree ment between the predicted and actual measured values of temperature of the body core as an index of short-term tolerable climate load. The tolerated time of work in the short-term, for Qmax = 50 W.h.m ^-2, gave an increase in body core temperature of 0.8-1.0 K. Heart rate mostly did not exceed 140 min^-1, although exceptionally rates over 150 min^-1 were reached.The authors recom mend limiting long-term work-heat (climatic) load generated at a high meta bolic rate (M > 80 W.m^-2 inclusive of the basal metabolic rate) by acclima tised males and females according to an SR of 270 g.h^-1.m^-2, and for non- acclimatised people by an SR of 206 g.h ^-1.m^-2. Our proposed limit for long- term work at low metabolic rates (M 80 W.m ^-2) for non-acclimatised and acclimatised persons is an SR of 147 g.h ^-1.m^-2. The short-term load which can be tolerated, because of heat storage in the body, for all categories of work ers is proposed as Qmax = 50 W.h.m^-2.

Key Words: Microclimate • Hygrothermal conditions • Toleration of high temperatures • Physiological limits • Climate chamber • Workplace hygiene

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