Human responses to cold and wind
Abstract: Cold is stressful for the human being and has physical, subjective and physiological effects. Body cooling must be prevented to provide for the worker's comfort and safety in cold workplaces. The effects of cold were studied in view of the two predictive cold indices that are mainly used, IREQ (Insulation Required) for whole body cooling and WCI (Wind Chill Index) for bare skin cooling. The indices had scarcely been validated by physiological studies. WCI is mainly based on theoretical calculations and physical measurements. The influence of thermal state, light physical activity and wind speed on heat flows, temperature, cardiovascular and subjective responses and respiratory function were investigated at climate conditions calculated to be at the borderline of risk-no risk. Eight to ten young and middle-aged subjects participated in the studies. The subjects were dressed in multi-layer cold-protective clothing. They sat, stood or walked on a treadmill at -6 to -22 °C for 10-90 minutes in wind (1-6 mls-1) and in the absence of wind. In one study the subjects were pre-cooled before the wind exposure. Even moderate wind speeds (2-6 mls-1) at -10 °C caused the systolic and diastolic blood pressure to increase significantly, more at higher wind speed. They remained elevated without compensatory bradycardia. The air velocity also had effects on the skin temperatures. In about a fourth of the wind experiments the face temperature dropped to 0 'C. Pain was commonly reported at conditions below the risk level for frostbite in Wind Chill Index. The criteria of IREQ concerning body cooling were fulfilled, but hand temperatures were lower than recommended. In addition, finger temperatures were below 15 °C, which resulted in reduced manual performance. An increased exercise level was more effective to reheat fingers after cooling at -22 °C than adding insulation. At -10 °C moderate exercise reduced finger cooling more than low intensity exercise, but only at < 1 mls-1. To be comfortable at low activity in cold it seems necessary to dress slightly more than indicated by IREQ and by thermal neutrality sensations. WCI seems to underestimate the cooling power of 5-6 mls-1 at -10 °C of bare skin (e.g. face). The results provided suggestions for improving and developing IREQ and WCI. Prediction models for cold risk assessment should consider the large individual variation. The observations of blood pressure responses to cold wind exposure indicate that special attention should be taken at exposure to cold wind of physically inactive individuals, hypertensive persons and patients with heart disease.
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