Document jBJe68rKvkv9ve1KwBJMVGbR9

1987 National Safety Congress ined: waste heat from nearby installations, warm return air from other underground workings, gcothormal heat from rock at depth, or tho heat contained in large bodies of water in lakes and rivers (even beneath lee-cappings In winter). In deep mining, ns at Kolar (in India), or on tire Witwntersmnd, or in Northern Australia, heat removal from tho air-stream is necessary. For this evaporative cooling is used or, alternatively, the air is passed over chilled coil systems. Although wo read of the rare case in mining that calls for humidification of on air stream, do-humidlficatlon is frequently more desira ble. Tho ultimate and eventual limitation in modem mining is depth, in which tho prob lems of heat, largely through geothermal gradients, can bo very serious. Combined cooling and de-humidification processes havo become necessary to provido desirable envi ronmental conditions in some mines. Avoldanco of humidification is attempted by re sorting to dry drilling and a reduction in tho use of water wherever possible, but such practico in turn gives rise to other problems. Quality control of the environmental at mosphere has not received as much attention in metal-mining as it has in collieries, but a greater awareness is evident nowadays amongst metalliferous mining engineers re sponsible for mine air-conditioning. The use of electrical analogue computers offers a rapid means of simultaneous control of a number of fnctors. Much remains to be dono in the study of turbulent resistance to flow in mine air streams and in the development of methods of ventilation network analysis. Acclimatisation is a factor in environments which claims our attention in'the industry under certain conditions. Tho extreme heat at extreme depths of mining give riso to problems of heat tolerance of the individual and, with them, those of acclimatisation. Tho adjustment of miners to extremes of en vironmental heat may bo prolonged and, even when acclimatized, gradual lowering of the overheated body to normal temperatures is important. Acclimatisation is also neces sary in the cose of high altitude locations; for example, in the Andes at elevations of 14,000-16,000 feet, where it takes the form of adjustment to oxygen deficiency and avoidance of over-exertion. Acclimatisation is a personal adjustment in the approach to, and withdrawal from, these unusual environ mental conditions. Dusts and Radiations. Tho hazards associated with dusts and ra diations are amongst tho most serious of all those with which tho mining engineer must contend but, like vontllntion, havo been re ceiving incrcnscd attention in recent years, particularly sinco tho insidious offccts of ra diations have been dramatically demon strated in tho uranium mines of this conti nent and elsewhere. Although much work has been dono on this important subject, much still remains to bo learned concerning dusts and radiations. Tho dust hazards derive from combina tions of particle size rango, freshness (or sur face reactivity), composition, and tho sus ceptibility of tho individual exposed thereto. Dust particles of pathological (or combusti ble) consequences are predominantly below 10 microns in size; that is, less than .0004 inch. Particles larger than lO microns are un likely to remain in airborno suspension in air streams of even modemto velocity. The haz ardous dusts characteristically havo a mean particle size in the rango of 0.5 to 3 microns, and generally the chemical reactivity of the minerollic material Increases with decreasing particlo size. Dusts below 10 microns, having no significant weight or inertia, tend to re main suspended somewhat indefinitely in an atmospheric environment. On the other hand, we know so littlo about actual dust particlo behavior, porticularly of the fibrous types such as asbestos-fine tube-like struc tures of almost constant diameter (0.5 micron) but of varying lengths. Do they tend towards preferential concentration, wafting about in'"!/ the atmosphere and settling under "hind ered" conditions? How do we assess atmos pheric concentrations of such dusts with ac curacy? Since dust particles may be electri cally charged, can they, or do they, attract to their surfaces coatings of even finer, more fissile dusts in parasitic fashion? Is this the reason for the intense activity of some essen tially silicious dusts (as on the Rand and elsewhere) where pneumoconiotic symptoms appear to havo been accelerated by some agency, perhaps extremely fino radio-active coatings? These arc questions that still re main to be settled. There are a number of categories into which dusts can be classified: (a) pulmon ary dusts, which are harmful to the respira tory system (such as silica, silicates, beryl lium ores, iron ores, and cassitcritic ores); 6