Thermal conditions in mining operations. Final report on CEC Contract 6245-11/8/049

A survey of climatic conditions in underground workplaces carried out in seven British collieries showed that what were regarded as hot conditions were characterised by only moderately high air-temperatures which were exacerbated by high relative humidities and low air velocities. These conditions were most often found at faces, face ends, headings and district roadways. Similarly, cold conditions were characterised by moderately low air temperatures, the effects of which were accentuated by the high air velocities often found in intake roadways and pit bottom areas.As human responses to hot and cold conditions have a degree of specificity, the research has developed along two independent lines: the assessment of thermal indices for hot mining conditions and the development of principles for the selection of clothing for use in cold conditions.A review of the literature on thermal indices suggested that four were appropriate for use in hot conditions: Effective Temperature American (ETA), Wet Bulb Globe Temperature (WBGT), Predicted Four-Hour Sweat Rate (P4SR) and the Index of Thermal Stress (ITS).Workrate was found to be a factor in the relationships between these indices. This finding was supported by the results of an experimental study which showed that metabolic heat in combination with environmental heat produced marked increases in both heart rate and core temperature.A subsequent field study indicated that mining work in hot conditions was of an intermittent nature and light to moderate in intensity. Under these conditions, metabolic heat load had little effect on the thermal load imposed on the workmen.A final laboratory study showed that under intermittent workload conditions in ETAs up to 28C, indices without workrate compoments (ETA and WBGT) predicted increased physiological strain. The practical implication for the British mining industry was that ETA, which is already in widespread use and easily measured and understood, is an acceptable index for predicting thermal strain.The mobile but low workload nature of the mining tasks undertaken in cold mining conditions, and a review of the literature on cold conditions, indicated that the best approach to improve workmen’s thermal comfort should be based on establishing the principle of protective clothing for mining conditions.In developing principles for the selection of such clothing, four main factors were found to affect heat loss from clothing assemblies:-a) the thermal insulation of the clothing fabric;b) the resistance of the fabric to wind penetration;c) the air exchange rate;d) the overall insulation characteristics of the clothingassembly.Air exchange rate was considered to be the most important because of the high air velocity compoment in cold mining conditions. The vailable laboratory technique which involved air exchange measurement was not sufficiently sensitive to measure air exchange rate in miners’ clothing assemblies due to the permeable nature of the fabrics used. A field experiment was designed, therefore, to investigate aspects of clothing materials and design in terms of subjective responses.The results of this study showed that thermal insulation of the garment was the major determinant of comfort in clothing assemblies for cold conditions in mining. Other factors identified included: one-piece or two-piece designs were equally acceptable in providing thermal comfort; and that the trial designs were felt to be less restrictive than existing clothing. “”