94 MINE VENTILATION. $35. every circumstance, is to prohibit the use of gunpowder in all fiery, bituminous mines. Shot-firing has, in all probability, to answer for more fatal casualties than some are inclined to ascribe to it. This does not happen so much in anthracite mines, from the fact that there is scarcely any dust floating in the air when compared with bituminous mines: however, we are not sure but that it may apply in some instances even to them. It is certain that people are maimed and burned by blasting, at distances varying from ten to a hundred and eighty yards, when there is no fire-damp present to cause such destruction; then, it is quite clear that this results, either from the simple force and flame of the shot on account of the weight of the charge, or from this force and flame assisted by the rapid combustion of coal-dust as it travels on its course, or from the force and flame assisted by an instantaneous emission of gas, in consequence of a partial vacuum being formed by the rushing blast. With a view of testing these assumptions, careful experiments were made, a description of which may be found in "Colliery Guardian," England, p. 13, vol. xxxii., the summing-up of which is as follows: "1. The flame from a blown-out shot, unassisted by gas or coal-dust, does not travel farther than five, or, at the utmost, ten yards, entailing little or no danger. "2. If coal-dust be present, even in a comparatively damp mine, the flame may not travel fifty yards. That in a dry mine of a high temperature this distance would be greatly exceeded; and since miners, as a rule, consider themselves safe at from fifteen to twenty yards from the point where the powder is used, a blown-out shot under these circumstances is a source of great danger. "3. That the violence of the blast from either gunpowder or fire-damp is much increased when coal-dust is present. "4. That, on any partial vacuum being formed in an underground coal-working, fire-damp will instantly issue in dangerous quantity; and there are fair grounds for assuming that a shot blowing out in the face of a narrow heading, and setting coal-dust on fire in its course, would, by its exhaustive action, produce such a vacuum, and might cause a serious explosion in a mine practically clear of gas. "5. Although no experiments have been made directly to test the result of coal-dust set on fire in air heavily loaded with fire-damp, there is every likelihood that such an occurrence would be attended with grave consequences. "6. That it is desirable that any system of blasting coal which entails heavy charges of gunpowder, and an 96 MINE VENTILATION. $36. unusual liability to 'shots blowing out,' such as blasting without side-cutting, or nicking, or using improper materials for stemming, should be discontinued. "7. A large body of flame, such as results from a very heavy charge or from a blown-out shot, is required to ignite coal-dust; that in blasting with charges not exceeding twelve ounces, accompanied by the proper preparation of holing and side-cutting, there is little liability of this taking place. "To discard all shot-firing means, in many mines, a considerable increased cost in the working of coal. But life is the first consideration, and the safety of the collier should be the one great object of the proprietor and manager. The opinion of the best mining engi neers is, that so long as shot-firing is allowed, even under the most favorable circumstances, so long will there be a certain amount of risk, while, in many cases where the plan is adopted, it often leads to most serious and fatal consequences.' 36. The third point, which should be earnestly considered, is efficient ventilation. There is no country in the world where such facilities are offered for good ventilation, because of the thick coal-seams; yet in very many instances managers appear to rely too much upon this advantage, and fail to conduct the air properly in its journey through the mines; and there are some that could not, although by law required, give the inspector a design of their ventilation. Thus it is not at all to be wondered at, when such gross negligence prevails, that accidents now and then occur. The cheapest method of obtaining more air is by splitting, and mechanical means. Enlarging the airways lessens the velocity, and is another, though costlier, mode of obtaining more air: in small seams it is, however, absolutely imperative. CHAPTER X. MEASURING THE AIR. 37. To measure air travelling through mines, various methods have been employed: those in most general use may be classed under three heads; viz., (a) Travelling at the same velocity as the air-current, and noting the distance passed over in a unit of time. (b) Determining from observation the rate at which small floating particles are carried along by the current, and assuming their velocities to be identical with that of the air-current itself. (c) By the use of the anemometer, or other instru ments. |