Physiological Observations on Men Working in Supposedly Limiting Environments in a West African Gold-mine

In recent years there has been renewed interest in the problem of limiting environments (Eichna, Ashe, Bean, and Shelley, 1945 ; Adolph, 1946). The appreciation that the body temperature may safely be allowed to rise a few degrees above the little arrow on the thermometer (Du Bois, 1948) has meant that the wet-bulb limit of 88? F., suggested by Haldane's work (1905), has long since been discarded. Almost any environment may be tolerated and even worked in for a short time ; thus Blockley and Taylor (1949) found that men at rest could tolerate a temperature of 240? F. for 20 minutes when the air was dry. Craig, Garren, Frankel, and Blevins (1954) consider the deter mining factor in voluntary heat tolerance is total heat storage, the best single estimate of which, they suggest, is the rectal temperature. In their tests the mean final rectal temperature at which the men gave up was 102? F. (S.D. 0-54). For exposures lasting several hours Robinson, Turrell, and Gerking (1945) have evolved a complex index of physiological stress, in which changes in skin temperature, sweat rate, rectal temperature, and heart rate are all taken into consideration. The M.R.C. Climatic Unit (1947), led by McArdle, after a long series of tests concluded that a single physio logical observation, the sweat rate, was sufficient to indicate the severity of a heat stress, and from their results a nomogram was constructed from which, given the relevant figures, the sweat production for a four-hour exposure could be predicted (predicted four-hour sweat rate or P4SR). From their obser vations on hyper-acclimatized subjects they con cluded that the threshold for intolerance was reached when the P4SR was 4-5 litres. Recent work on the same lines reported by Ellis, Ferres, Lind, and Newling (1954) in Singapore has shown that the limit suggested by McArdle was substantially correct. In Fig. 1 the London and Singapore l mits for men in overalls and those suggested by Robinso and others (1945) are plotted together ; all three groups of workers also set the upper limit of tol rance for men dressed in shorts working at to 2 m t. (1 met. = 50 kg. cal./sq. m./hr.) at abo t the same area on the psychrometric chart. Working conditions which approach these toler ance limits have been described several times in mines ; for example, by Weiner (1950), who found working temperatures in Rand mines of 93-7? F. dry-bulb, 92-7? F. wet-bulb, and Caplan (1944) who reported working places in Indian mines with a dry-bulb temperature of 112? F. and a wet-bulb on of 96? F. In both places collapse from heat occurs, but it does not seem to be a major problem until even higher temperatures are reached. On the other hand the amount of useful work that can be done is severely limited under such conditions ; Caplan and Lindsay (1946) found that only about one hour's good work was possible when the wet bulb r ached 93? F. or the effective temperature 96? F.; this corresponds to the 50% failure line de ermined by Ellis and others (1954). In a Nig rian colliery, where conditions were uncomfortable rather than severe, the workers avoided heat stress by taking frequent rests and by tak ng time off in cooler, well-ventilated roadways whenever they could (Ladell, 1948b). Conditions in West African gold-mines are more severe than in the collie y, and through the courtesy of the Ashanti Goldfields Corporation the physiological obser vations reported here were made on the workers in one of their deep mines at Obuasi. These observa tions show how the West African miners react in situations where conditions are near the accepted tolera ce limit. From the ventilation reports the stope tempera tures in this mine varied from 82 to 97? F. and the wet-bulb temperatures from 81-5 to 96? F. The Ill