Show mechael mechanically cally produced venti ventilation aaion in in metal mines BY GEORGE RICE mechanically produced ventilation or of mines and the coursing of air throughout their workings has been regarded until the last few years as necessary only in coal mines the more or less haphazard ventilation of metal mines is in striking contrast to the high order of engineering shown in other departments of metal mining operations ventilation of coal mines on account of inflammable gases given off by the strata or the loss of oxygen of the all air through absorption by the coal made the positive coursing or circuiting of the air current a vital necessity this was waa recognized a century ago after serious explosions of fire damp had occurred occurred d although coal mining operations were on a very small scale at that time notwithstanding the slow development of positive ventilation in metal mining op orations erat ions mechanically produced ventilation i of metal mines re eions taken from the hoover translation of Agri colas book 1 I will now speak of ventilating machines if a shaft is very deep and no tunnel reaches to it or no drift from another shaft connects with it or when a tunnel is of great length and no shaft reaches to it these devices are of three genera the first receives and diverts into the shaft the blowing of the wind the second genus of blowing machine is made with fans fang and is likewise varied and of many forms for the fans are either fitted to a windlass barrel or to an axle blowing 4 A V Y A 4 j PA 41 va W when a eills of great length and no shaft an early start agricola in his book describing the mining practice of the sixteenth century in the hartz mountains repeatedly refers to ventilation ti the following are some quota then the air does not replenish itself in such a case it weighs heavily on the miners causing them to breathe with difficulty and sometimes they are suffocated and burning lamps are also extinguished there is therefore a necessity for machines IN which enable the miners to breathe easily and carry on their work 4 machines of the third genus which are no less varied and of no fewer forms than those of the second genus are made with bellows for by its blasts the shafts and tunnels are not only f furnished urnis hed with air through conduits or pipes but they can also be cleared by suction of their heavy and pestilential va pours many devices Agri colas drawings show many varieties of ventilating devices vices some dependent as indicated in the above quotations on the effect of the wind and others are the predecessors of the centrifugal fans several of the drawings show large feath ers set in the axle others show wood blades or paddles arranged as in the later guibal fan apparently however the proper arrangement for admitting the air to the fan fail at the axle had not yet been discovered in the drawings the air appears to enter a slot on the circumference of the casing and is discharged through a wooden coti conduit dult at another place on the circumference cum ference presumably y however the file action off the fanjas fan was I 1 improved through the le leakage ak igo of af ille the I 1 wooden I 1 sides so that accidentally I 1 it way may not have been so inefficient in design the drawings seem to indicate ab Z 4 7 4 5 1 1 an k moo 41 A 7 al A continuous current of air should reach every part of the mine that the use of brattices bratt ices in shafts and ventilating ti doors was understood although there is no indication that a circuit of the air was maintained main bained away from the shaft or beyond where a sh shaft a ft intersected drift workings except by wooden pipes little advance seems to have been made in metal mining ventilation for the years following until compressed air drills came into use th then n the exhaust from these was and ordinarily still is regarded as furnishing bishin sufficient air in the working place when the drill is not running if the atiq atmosphere is oppressive in the heading or s or aris is bad following blasting the comprised com presed air is allowed to blow direct from an air pipe outlet undoubtedly in small metal mines or those in which there is no considerable sid erable amount of noxious gas given off or where workings are a short distance from tile the drift mouth or shaft this may be sufficient in most metal mines owing to the or ore formation generally having length along the strike and depth vertically or to the dip alp but bui generally not great width difference in temperature between the lower workings and the outside atmosphere generates aerates dir air currents when secondary connections have been made to the surface inflammable gases rare iffla inflammable gases are rarely encountered t e red in metal mines and 9 generally ene rally there ther e is a little absorption of 0 oxygen X agen by the ore or inclosing walls although in mines in which there is much timbering it has been found that there is considerable absorption of oxygen by the timbers due to bacteriological action nevertheless thousands of samples of air that have been gathered by the bureau of mines in metal mines indicate that except after blasting it is rare when the air has a considerable amount of impurity occasionally as in the cripple creek district metal mines encounter large amounts of pure nitrogen gas residual in the strata such mines can only be worked by the employment of a plenum pressure system of ventilation in general however the chief air impurities in metal mines arise from blasting in the ca case se of long drainage tunnels the rule is to ventilate with fans and air pipes and it is obvious that it is an economic advantage to quickly ventilate the heading after blasting so that the miners may get back to their work as soon as possible gradual introduction in great ore bodies such as are found at butte in the lake superior iron and copper mines in the copper mines of the compressed air when there is a consider consid able volume 0 of noxious or p poisonous onOus gases caf present as from blasting is ext extremely reineld in i efficient both in swee sweeping away the sr noke and gases which it tends merely to stir 1 up and from a mechanical efficient effi efficiency cien cy stand point in using air which is as usually cora coal pressed inefficiently to a high pressure dessure res sure and liberating it without doing in mechanical ech anical work at atmospheric pressure tho ohp only remedy is to arrange as far as P possible a circuiting of air supplemented by booster fans fails the two exits it is hardly necessary in this day to argue the necessity of having two cwb means of exit from a mine as this is the requirement in most state metal mining laws proba probably b ay over 95 per cent of the metal mines of the country which have reached a permanent basis of ore production have two exits and the remainder are probably Y putting in such second exits as rapidly as it can bedone where there are two such exits 0 one 11 naturally becomes the and the other the downcast unfortunately however these conditions sometimes change with the season and during such change or approaching it the natural ventilation underground is asin in sufficient hence in such mines there is a necessity for the use of effans fans in very deep mines such as the copper mines of the lake lahe ap d 0 X 1 15 A A A P S E Q I 1 PM 1 I x wk V 4 it Is an economic advantage to ventilate the head quickly after blasting soTha olle miners may get back to their work southwest and especially in the deep and extensive gold mines of south africa there has been a gradual introduction of mechanical ch anical ventilation methods apart from any dependence on compressed air at the faces attempting to ventilate by means of normally the superior district and the downcast conditions do no not reverse treverse very is natural main up casting current such strong it then becomes a pr problem kroblen interest in afie in a special case whether yh ether oj or not in current of curre of safety to prevent reversal the case of a mine fire in the downcast it is not best to install a large fan which may never ibe be needed except for fire protection tec tion however in the great majority of mines a s strong rong non reversing current due to the difference in temperature in the casting up and down casting shafts cannot be obtained this being the case it is highly important both tor for fire protection and for a positive circuit of air through the mines that fans shall be used great variety of conditions the great variety of conditions found in metal mining in the united states varying from typical figure veins to the great and irregular iron ore bodies of the lake superior district makes it impossible to lay down as exact a procedure as is usually reg regarded added as a necessity in planning coal mining developments nevertheless erth eless it will be generally conceded that a great deal more might be done in the future than has been done in the past if preliminary planning of a ventilating system is borne in mind particularly in developing low grade deposits the volume of which has been more or less determined in advance by prospecting while metal mining laws and modern practice require two exits and recognize the necessity of air down casting in one shaft or and returning through another shaft or audit or tunnel the necessity for provisions for circuiting the air through the body of the mine has not been well recognized with the result that in some of the great mines of the I 1 united states the ventilation is of the most haphazard or badly arranged character often the writer has had occasion to observe that the main fan placed underground is ineffective because part of the air discharge has been circuited round and around therefore even when the percentage of impurity in the air might be low it did no not take care of one of the most important features of metal mines ventilation in deed dee mines i e to keep the current temperature below that of the mine walls it is not always a question of depth or natural heat of the strata but where large masses of timber are employed especially in the caving system employing a timber mat the temperature is frequently far greater immediately under the mat than it is in the deeper development levels care in devising system it is believed that if the same degree of care were taken in laying out in advance the ventilating system that is given to laying out the levels drifts and cross cuts and raises for extracting the ore body a great deal of the diff difficulty of physiological si nature now experienced by the miners in certain districts would be prevented these troubles are not simply those of temporary discomfort of the workers but their health is likely to be affected and make them liable to contract diseases lessening their working efficiency and thus in consequence decreasing the earning of the mine ventilation therefore becomes a matter of economic importance it is difficult to speak of specific mines or districts without causing unfortunate comparisons but that the problem is an acute one in many districts will be readily admitted by most mining authorities another phase of the physiological problem concerning workers in hot mines is that it is not alone the high temperature of the air but whether or not the air is in motion the experiments of dr haldane of oxford ane celebrated physiologist brought out strikingly that in still hot air the body is editions found in the united unite estates dS states tates prevent formulating exact specifications for a ventilating ti scheme which would fit all conditions but in order to bring out discussion which it is hoped will follow these suggestions the following general principles are mentioned which may be of guidance in planning the ventilating systems of now new mines or in adapting the arrangement of old mines as far as is possible to do so 1 that there shall be a permanent and permanent downcast shaft 2 that the downcast shaft shall be as far as practicable the shaft in which the men are hoisted and lowered it may or may not be the main ore hoisting shaft the object being that in case of fire in the 10 NINE k r 5 P ak MS 4 W A cut showing great advance now being made in ventilating systems this is a modern installation which Is coming into general use note the workman carrying several lengths cut furnished by bro bag co st louis alo enveloped with a film of air at or near blood heat and the skin is not cooled by evaporation of the sweat but if the air is in motion unless it is saturated which it seldom is evaporation occurs and thus the skin is cooled the writer recalls a case where in a certain there was no movement of the air the miners complained of the heat and froni from time to time they went into a nearby crosscut where there was a strong current of air and were comfortable although in the latter place the temperature w was as actually several degrees hotter than in the former specifications for system the tremendous variety of mining con mine the main maim hoisting arrangements for men will be available and if practicable this shaft and its landing shall be concreted or otherwise fireproofed fire proofed and back of each landing there shall be a fireproof door to 0 protect from tho the workings beyond 3 that the main shaft shall extend to the lowest workings so that the fresk bresli air may go to the bottom of the mine and then ascend on either side through the workings to the shaft sufficient iclene splits of air to be taken off on the different levels to provide for proper ventilation on these levels the returns to be taken around the downcast shaft by crosscuts cross cuts or concreted bridges main fan on surface 4 that the main ventilating ekl lating fan be placed on the surface the fan to be of fireproof construction and with fireproof housing this to be a reversible fan generally die most convenient arrangement would be to place it near the collar of that shaft which is not the main hoisting shaft of course a tunnel or slope mouth would be equally as good so 0 as to avoid an air lock therefore the fan would normally be an exhaust fan but as previously stated it should be reversible to provide for emergencies 5 the fan should ibe be of sufficiently large size so as to take care of the largest volume of air which is likely to be sary for at least five or six years to come and it should be able to deliver and draw air at a pressure in excess of that which could be produced by maximum natural causes that is the maximum notice head of the air column due to the maximum difference which may obtain of temperature pera ture of the mine air and of the outside air in the coldest or the warmest day of the year for undeveloped mines such figures have to be more or less conjectural and so it is often necessary to make assumptions from past experience in general the main fans at metal mines are entirely inadequate and fans such as are employed in large coal mines should be installed in metal mines the workings of which are expected to be of large extent and employ many men underground by this is meant fans which will discharge from to cubic feet of air per minute against pressure measured by two to six inches of water gage on account of the fire risk it is not good practice to place the main fan underground and moreover there is usually liability of the air short circuiting that is going around and around and not being discharged to the surface of course there are special conditions where the ground is badly near the outcrop and the leakage of air would be too great to place it at the surface but the conditions are exceptional where the openings cannot be sealed iby by surface covering or clay filling booster fans are a necessity 6 booster fans are necessary in exploratory drifts and in making dinzes or raises and in high new devices in the way of canvas pipes and hanging arrangements range ments for same have |