Heat exhaustion in a deep underground metalliferous mine

Objectives-To examine the incidence, clinical state, personal risk factors, haematology, and biochemistry of heat exhaustion occurring at a deep under ground metalliferous mine. To describe the underground thermal conditions a ssociated with the occurrence of heat exhaustion. Methods-A 1 year prospective case series of acute heat exhaustion was under taken. A history was obtained with a structured questionnaire. Pulse rate, blood pressure, tympanic temperature, and specific gravity of urine were me asured before treatment. Venous blood was analysed for haematological and b iochemical variables, during the acute presentation and after recovery. Bod y mass index (BMI) and maximum O-2 consumption (V) over dotO(2) max) were m easured after recovery. Psychrometric wet bulb temperature, dry bulb temper ature, and air velocity were measured at the underground sites where heat e xhaustion had occurred. Air cooling power and psychrometric wet bulb globe temperature were derived from these data. Results-106 Cases were studied. The incidence of heat exhaustion during the year was 43.0 cases 1 million man-hours. In February it was 147 cases / mi llion man-hours. The incidence rate ratio for mines operating below 1200 m compared with those operating above 1200 m was 3.17. Mean estimated fluid i ntake was 0.64 l/h (SD 0.29, range 0.08-1.50). The following data were incr eased in acute presentation compared with recovery (p value, % of acute cas es above the normal clinical range): neutrophils (p<0.001, 36%), anion gap (p<0.001, 63%), urea (p<0.001, 21%), creatinine (p<0.001, 30%), glucose (p< 0.001, 15%), serum osmolality (p=0.030, 71%), creatine kinase (p=0.002, 45% ), aspartate transaminase (p<0.001, 14%), lactate dehydrogenase (p<0.001, 9 .5%), and ferritin (p<0.001, 26%). The following data were depressed in acu te presentation compared with recovery Cp value, % of acute cases below the normal clinical range): eosinophils (p=0.003, 38%) and bicarbonate (p=0.01 1, 32%). Urea and creatinine were significantly increased in miners with he at cramps compared with miners without this symptom (p<0.001), but there wa s no significant difference in sodium concentration (p=0.384). Mean psychro metric wet bulb temperature was 29.0 degrees C (SD 2.2, range 21.0-34.0). M ean dry bulb temperature was 37.4 degrees C (SD 2.4, range 31.0-43.0), Mean air velocity was 0.54 m/s (SD 0.57, range 0.00-4.00). Mean air cooling pow er was 148 W/m(2) (SD 49, range 33-290) Mean psychrometric wet bulb globe t emperature was 31.5 degrees C (SD 2.0, range 25.2-35.3), Few cases (<5%) oc curred at psychrometric wet bulb temperature <25.0 degrees C, dry bulb temp erature <33.8 degrees C, air velocity >1.56 m/s, air cooling power >248 W/m (2), or psychrometric wet bulb globe temperature <28.5 degrees C. Conclusion-Heat exhaustion in underground miners is associated with dehydra tion, neutrophil leukocytosis, eosinopenia, metabolic acidosis, increased g lucose and ferritin, and a mild rise in creatine kinase, aspartate transami nase, and lactate dehydrogenase. Heat cramps are associated with dehydratio n but not hyponatraemia. The incidence of heat exhaustion increases during summer and at depth. An increased fluid intake is required. Heat exhaustion would be unlikely to occur if ventilation and refrigeration achieved air c ooling power >250 W/m(2) at all underground work sites.