Sivut kuvina



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obtained as shown by § 32. The pressure passing 50,000 cubic feet, we find aggregates 8.328 pounds; then

√8.328: √6:: 50000 : 42400 cubic feet

the actual quantity, as is shown by the table.


34. As yet no rule has been established as to the quantity of air necessary for ventilating mines of dif ferent capacities: consequently, sometimes as much air is sent into a mine employing two hundred persons as there is into one in which twice that number are constantly engaged.

Scientifically ventilated mines contain a certain allowance of air for each person working under ground, as well as for each light and horse; also for various other purposes. Some persons think they can determine in a general manner the volume of air necessary for a mine, basing it upon the following single element, the number of miners employed, and giving to them a greater or less volume of air, varying with the presence or absence of fire-damp. Let us see if this be correct, and, to do so, assume that each workingman, exclusive of

horses and lights, requires one hundred cubic feet per minute, taking as examples two mines equally developed, although, by reason of the nature of the coalseam and the mode of working, the tonnage hewn by each man may be different, and only require sixty men in the first mine, whilst the second requires a hundred and fifty men.


The first, we will say, is from necessity wrought in two workings 6' x 5'. The volume per man being 100 cubic feet, the total volume required is 6,000 cubic feet per minute, which, divided by the area, 303060 square feet, gives 100 feet per minute as the velocity of the air. In the second case, one airway is required with an area of 8' x 5' 40 square feet. The total volume. circulating will be 100 x 150 15,000 cubic feet per minute, and the velocity will be 377.5 feet per minute. The first velocity will be insufficient to sweep away the gas, and prevent the heating of the air; while the other is too great, and would incommode the workmen. Thus a volume of air exclusively founded on the number of men employed is incomplete. The extreme limits of velocity which largely regulate the temperature, and indirectly the capacity of the air for water-vapor-must be fixed. To do this, a record of the development of the working; the method of working; the nature of the seam; the splits, if any, or, if not, the main current; and



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the more or less abundant production of gases, must be kept, as it is impossible to fix in a lump otherwise the volume of air necessary for a fiery mine, where the evolution varies in such great limits. On account of the great complication of such calculations, no general system can be established. “It appears, under the circumstances, to be indispensable to proceed by analogy, by classing mines according to the more or less favora ble conditions for ventilation in which they are situated, and to form groups, to the members of which a single and absolute rule can be applied."

In some mines, of course, more air is required than in others; but, for sanitary purposes alone, 120 feet per minute is quoted as the minimum for each man and boy; but, where gas is given off, twice that amount should be allowed. No person should be allowed to work in a stagnant atmosphere, while the working-places and goaves where the gases congregate should have a supply of air large enough to dilute and deprive them of their power. In all excavations where air is renewed, and in the galleries of mines in particular, carbonic-acid gas is continually found in more or less quantity. The ventilation should be sufficient to draw it constantly away, and to keep that quantity which is mixed with the air beneath that limit beyond which it would become injurious to the workmen.




little or no gas is given off. The cost of fan-ventilation is not as great as the furnace, although the first cost is larger. As before stated, enlargement of airways, and judicious division of the current into several splits (which should begin as near as possible to the downcast), will bring the air much purer and cooler to the miners, and also greatly increase the ventilation.


35. Much has been written and said upon this subject, yet every now and then the public is startled with news of a recent explosion where numbers of lives have been lost. The investigations which follow are not always satisfactory, either to the families of the deceased or the managers. Instances may be cited where the injured have received the blame for the negli gences of either the manager or his "fire-boss."

There are laws in some of the States which require the managers to allow each miner a certain quantity of air. Whenever there is "bad air," the miner should inform the "mine-boss," and, in case the evil is not speedily remedied, report the fact to the "mine-inspector." Miners should not neglect to do this, even if it costs them "their job;" because they risk the lives of

1 See Sect. 7, Pennsylvania Mine Laws.

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