Assessing the Heat Stress and Establishing the Limits for Work in a Hot Mine

Abstract

The management of the mine at Mount Isa, Queensland, Australia decided to enquire into the following questions with regard to men working underground in hot conditions: (a) Which of the various heat stress indices predicts most accurately the effects on workmen of the various heat stress factors which occur in the mine at Mount Isa? (b) How best should the limits of heat stress be judged at which the normal 8-hour shift should be reduced to a 6-hour shift, or at which work should be stopped? With these objects in mind, oral temperatures were measured on 86 workmen after three hours of ordinary work in the mine and also on 36 occasions on 29 volunteers after three hours of stepping on and off a stool at a work rate of 1,560 ft. lb./min. These men were studied in different environmental heat stresses over the range that occurs in the mine. Dry bulb air temperatures (D.B.), wet bulb temperatures (W.B.), velocity of air movements, and globe temperatures (G.T.) were measured in the micro-climate in which each man worked. An estimate was made of the work rate of the 86 workmen. From these estimates and measurements, the predicted 4-hourly sweat rate (P4SR) and corrected effective temperature (C.E.T.) values were determined for each heat stress condition. P4SR values varied between 0·9 and 6·5 and C.E.T. between 70° and 95°F. Correlation coefficients were calculated between oral temperatures and W.B.s, C.E.T.s, and P4SRs and are 0·51, 0·64, and 0·75 respectively. Further analysis was confined to C.E.T. and P4SR. Plots of oral temperature on P4SR for conditions where G.T. was more than 10°F. above D.B. were found to fall well below the rest of the plots, indicating that P4SR exaggerates the effect of mean radiant temperature. These data were therefore excluded from the rest of the analysis. Regression equations were calculated for oral temperature on P4SR and for oral temperature on C.E.T. for (a) men `on the job', for (i) conditions where D.B. was more than 10°F. above W.B. and (ii) for conditions where D.B. was less than 10°F. above W.B., and (b) for men `stepping'. This analysis showed that one overall regression line can be used for all three conditions for oral temperature on P4SR, but for oral temperature on C.E.T. at least two different regression lines would be needed. Also the correlation coefficients between oral temperature and P4SR were generally higher than between oral temperature and C.E.T. For the prediction of oral temperature in the mine at Mount Isa the P4SR index is to be preferred to the C.E.T. scale. These results indicate that the emphasis given to G.T. in the P4SR index is too great. A multi-variance analysis of the P4SR index shows that, in the middle of the range of heat stress conditions examined, a unit change in P4SR would be obtained by about the same change in W.B. and G.T. This is at variance with the present results and also with the experimental findings of the M.R.C. Climatic Physiology Unit at Singapore. It appears, therefore, that the P4SR index should be revised in this regard. When ...

Heat illness in the U.S. mining industry

“…It is likely that the same processes occur in the US. By way of contrast, work rates used to be paced in South Africa [Wyndham et al, 1967], and it is likely that miners suffering heat exhaustion continued to work and went on to develop heat stroke.…”

A Field Evaluation of the Physiological Demands of Miners in Canada's Deep Mechanized Mines

“…Many of the issues affecting work in hot environments, which were first addressed in South African mining operations in the 1920s, remain unresolved. (1)(2)(3)(4) Although limits for work and heat stress in hot mines have also been partially examined in Germany, (5,6) Turkey, (7) India, (8) Australia, (9) and the United States, (10) the need to combat personnel heat exposure in Canadian mines is comparatively new but becoming an increasingly important issue. In recent years, the economic incentive to mine deeper has created new and unique challenges for the industry.…”

Heat exhaustion in a deep underground metalliferous mine

“…In 1967 Wyndham et al developed thermal exposure limits for underground mining designed primarily to prevent heatstroke 12. These limits have been used at this mine and although no case of heatstroke has been recorded, heat exhaustion and heat cramps remain common.…”