April 15, 1886] 



NATURE 



569 



officials and woilimen in the mine than liy any attention to such 



explosions have been made the subject of careful study and com- 

 prehensive experiment by numerous workers since attention was 

 first drawn, about forty-two years ago, by Faraday and Lyell to 

 the functions exercised by coal-dust in "aggravating and ex- 

 tending the injurious effects of fire-damp explosions." The 

 results and conclusions which have been arrived at in this direc- 

 tion, and to which the labours of your Commis-ioners have con- 

 tributed, are sufficiently complete and definite to warrant the 

 following authoritative statements : — The disastrous effects of 

 fire-damp explosions in coal-mines are almost always aggravated 

 and extended by the existence of coal-dust in dry mine-workings 

 and roadways. A gas explosion in a dry mine, even if only of 

 comparatively trifling nature, will raise and inflame coal-dust 

 existing at the seat of the explosion or in the vicinity ; the 

 flame attending the explosion will be thereby increased and 

 carried to more or less considerable distances, and may thus 

 become cimmunicated to any accumulations of explosive gas- 

 mixture which may exist in goaves or other lurking places at a 

 distance from the seat of the original gas explosion. 



The firing of an explosive in shot-hole of a strength which is 

 in excess of the power applied, or which has not been sufficiently 

 tamped, will result in the almost complete projection of the 

 highly-heated products of explosion and of a more or less con- 

 siderable body of flame from the mouth of the hole, as from the 

 bore of a gun ; it thus produces what is kno \n as a blown-out 

 shot. And further, if the charge of explosive is decidedly 

 greater than that necessary to perform the desired work in the coal 

 or stone where it is ai:)plied, a more or less considerable projec- 

 tion of highly-healed products of explosion will nlso take place, 

 and effects similar to those of a blown-out shot will Vie produced. 

 The production of a blown-out powder shot in a mine-working, 

 in the entire absence of coal-dust, or in a wet mine, is not 

 attended by the projection of flame to a very considerable 

 distance, but the flame thus projected is much increased in 

 volume if, as is frequently the practice, dry or slightly damp 

 small coal has been used as stemming for the shot. If a blown- 

 out powder-shot be produced in a dry locality where coal-dust 

 exists in more or less a'umdance, the flame projected by the 

 shot is sure to be considerably increased and extended by 

 the ignition of portions of the dust-cloud which is raised 

 by the rush of air occasioned by the firing of the shot. A 

 result of this nature will be produced even if the air in the 

 vicinity of the blown-out shot is entirely free from fire- 

 damp. Unless the coal-dust which exists in the immediate 

 vicinity of a blown-out powder-shot is dry, very finely- 

 divided, and of a very highly inflammable character, the 

 propagation of flame from the shot by the raised dust will 

 only take place to a comparatively limited extent if the atmo- 

 sphere in which the dust is raised be entirely free from fire-damp. 

 It is, however, well established that, even when the air is quite 

 free fro 11 fire-damp, an exceptionally inflammable coal-dust, in 

 a very finely divided and diy condition and existing in abun- 

 dance in the immediate vicinity of a blown-out shot, may, when 

 raised by the shot, be ignited so readily, and carry on the flame 

 so rapidly, that i: may produce explosive effects of a similar 

 character to those caused by a gas explosion. The flame, as it 

 rushes along, if fed by fi eshly raised dust, may extend under 

 these circumstances to very considerable distances, with results 

 resembling, in their disastrous nature, those of explosions origin- 

 ating with, and mainly due to, luc da!iip. If a blown-out 

 powder-shot occurs in a localit}" wlicr'/ lln atmosphere contains 

 a small proportion of fire-damp (evi n not idnivc two parts in 100 

 of the air), the presence of dry, fine, and porous dust, even if 

 it be only comparatively slightly inflammable, may give rise to 

 the explosive propagation of flame to distant localities, where 

 either accumulation, of inflammable or explosive gas-mixture 

 (as in goaves or old working places), or deposits of very inflam- 

 mable dust, may take up the explosion and still further extend 

 its disastrous effects. Wherever a coal is worked which con- 

 tains inflammable gas, the atmosphere in the vicinity of the 

 workings, however efficient the ventilating arrangements, will 

 at one time or another, and, it may even be said, generally, con- 

 tain some small proportion of fire-damp. Mines have hitherto 

 been considered free from fire-damp when the search for gas by 

 means of a lamp flame has been unattended by the appearance 

 of a cap upon the flame or by an elongation of the flame. This 

 test, however, fails to indicate the presence of fire-damp, if the 



atmosphere contains less than from 2 to 2 '5 per cent, of its 

 volume of marsh gas. Such a slight contamination of the 

 atmosphere by fire-damp is not only sufficient to greatly enhance 

 the dangers due to the existence of dust in any abundance in a 

 dry mine-working, as already described, but is also sufficient 

 actually to give rise to the production of an explosive mixture 

 with dust raised in it by a blown-out shot. Small proportions 

 of gas, such as are referred to, when existing in the atmosphere 

 of a mine, can now be detected by more delicate gas-indicators 

 than a lamp flame; but, while a knowledge is thus afforded of the 

 presence of gas, it remains impracticable to prevent such slight 

 contamination by fire-damp of the air of a mine near the 

 working places. 



It will be seen from the foregoing that such contamination, 

 although quite insufficient to constitute in itself a source of 

 danger, does become dangerous if dust co-exists with it, in abun- 

 dance, in diy mine-workings, if powder-shots are fired in such 

 workings. No means are at present known by which security 

 can be attained against blown-out shots during blasting in hard 

 coal or in stone, and the use of powder in coal is sometimes 

 attended by the emission of flame, even when blown-out shots 

 are not produced. It follows from the foregoing that the firing 

 of powder-shots in a dry mine-working where dust exists in 

 abundance must always be liable to be attended with disastrous 

 results if the air in such a locality is contaminated by fire-damp, 

 even to so small an extent as in the proportion of two volumes 

 in 100 volumes of the air of the mine. The constant removal 

 of accumulating dust from the workings in di-y mines, to such an 

 extent as to guard against the raising of any considerable quantity 

 of dust where shots are fired, coultl scarcely be so thoroughly 

 carried out. in any but very exceptional cases, as to constitute by 

 itself an effectual precaution. The application of water to the 

 laying of dust in roadways has been applied here and there with 

 some amount of success, but the effective adoption of such a 

 measure in or near the working places is in some instances at- 

 tended with practical difficulties. Unless very copious watering 

 be resorted to, it would be inePectual in guarding against the 

 dangers arising from the firing of powder-shots in dry and dusty 

 workings where the air may contain some small proportion of 

 fire-damp. The employment of hygroscopic or deliquescent 

 salts in conjunction with water has not been found a trustworthy 

 means of maintaining dust in a safely moist condition. The 

 dangers which attend the firing of powder-shots in dry mine 

 workings where dust exists in abundance, and where the air may 

 contain even only a small proportion of fire-damp, can therefore 

 not, with our existing knowledge, be effectually guarded against, 

 except by combining the removal of dust as far as practicable 

 with very copious watering. The obvious inference to be drawn 

 from the foregoing is that a due regard for the safety of those 

 employed in mines, where the conditions above indicated pre- 

 vail, precludes the use of powder, unless the precautions just 

 specified are effectually applied. The results of extensive prac- 

 tical experiments, carried out by ourselves and by others, have 

 demonstrated that the abolition of the use of powder, where the 

 conditions above indicated prevail, will not generally involve any 

 formidable inconvenience, because the work which is accom- 

 plished by its employment, both in coal and in stone, can now 

 be performed with equal efficiency and at very little, if any, 

 greater outlay, by one or other of the following available alterna- 

 tive means : — («) In some coal-seams the lime-cartridge will per- 

 form work quite equal to that accomplished with powder, at no 

 greater cost, and with absolute immunity from risk of explosions ; 

 \b) mechanical appliances exist which will do efficient work, not 

 only in some kinds of coal, but also in some stone or shale over 

 or underlying coal ; {c) the so-called "high " or violent explosive 

 agents, which are represented by dynamite or gelatine-dynamite, 

 and by gun-cotton or tonite, can now be applied, not only for 

 working economically in stone or shale, but also for coal-getting, 

 by using them in conjunction with water, according to one or 

 other of the methods described in this report. 



The "high" explosives may be used, as indicated in {c), with 

 security against the ignition of coal-dust thickly suspended in 

 air, by a blown-out shot or by the effects of an over-charged 

 hole, even when the air contains some small proportion of fire- 

 damp. One very simple method of using the " high " explosives 

 in conjunction with water, included in (c), which may be supple- 

 mented by the use of ordinary tamping for securing the best 

 working results, has, so far as several severe tests have shown, 

 afforded a complete safeguard even against the ignition of an 

 e.xplosive mixture of fire-damp and air by a blown-out shot. 



