570 



NATURE 



[February 22, 1912 



The high average of the last period of nine years is 

 due to the occurrence of two great explosions, admittedly 

 of coal-dust, in which 480 men were killed. To my 

 pf'r«;onal knowledge these two explosions might have been 

 avoided had ordinary precautions been taken of the kind 

 rofcrred to above. But for these two explosions the aver- 

 age of the last nine years would have been 80 instead of 

 134, or the lowest on record for sixty years. 



In the United States, the greatest coal-producing country 

 in the world, the coal-dust que.stion attracted scant atten- 

 tion until 1907, when the total death-roll from coal-dust 

 explosions, so-called " windy shots," and gunpowder ex- 

 plosions reached the appalling figure of 1148. 



In 1908 Congress was induced to vote a sum of money 

 for the investigation of mine explosions ; the Geological 

 Survey was entrusted with the work, and on December 3 

 of the same year a testing station that had been built at 

 Pittsburg during the interval was formally opened. 



The recent experiments have corroborated the announce- 

 ment made many years ago that an explosion capable of 

 (iropagating itself through the workings of a mine cannot 

 be initiated unless the cloud of dust and air is both large 

 dense, and is ignited by a flame preceded by an air- 

 wave. 



The quantity of dust ordinarily in the air, or raised bv 

 the passage of a train of mine waggons, however rapidly 

 they may be moving, is far too tenuous to be in the 

 slightest degree inflammable. 



M. TafTanel states ' that the minimum quantity of the 

 very highly inflammable coal-dust employed in his experi- 

 ments that must be suspended in still air before the mixture 

 can be ignited by a large flame like that of a comet lamp 

 is I lb. to 80 cubic feet ; that the probability of a dust- 

 cloud of that density being formed in any niine working 

 under normal conditions is extremely feeble ; and that even 

 " in working plact^s called very dusty or smoking the 

 density does not exceed more than a few grams per cubic 

 metre " (say, un(>-third of an ounce in 80 cubic feet, or 

 about one-fiftieth of that required to render the mixture 

 inflammable). 



I mention these facts in order, if possible, to counteract 

 the exaggerated notions that have sometimes of late been 

 expressed regarding the dangerous nature of coal-dust 

 even in a state of quiescence, some persons seeming to 

 credit it with qualities akin to those of gunpowder. 



The relative fineness of the dust, proportion of volatile 

 matter contained in it, and quantity present per unit of 

 length in the experimental gallery determine the velocity 

 of the flarne and the pressure attained by the explosion 

 at any point. When all three conditions are favourable 

 the velocity and pressure increase rapidlv with the distance 

 traversed, and if the distance is sufficiently great the 

 pressure is liable to burst the gallery, as it did in one or 

 two instances— at .Altofts and Li^v'in. As the dust for 

 experiments is prepared mechanically from pure coal, and 

 may be made far finer than the average of that found in 

 any colliery, it follows that the velocity and pressure of 

 explosions in the artificial galleries mav'be, and no doubt 

 m many cases are, far greater than those that occur in 

 an explosion in a dry and dusty mine, for in the latter 

 the dust swept up by the airwave which precedes the 

 flame contains a mixture of coarse and fine particles of 

 both combustible and incombustible matter. But the 

 coarse particles of both and the fine particles of incom- 

 bustible matter reduce the temperature of the flame, and, 

 consequently, both its velocity and pressure must neces- 

 sarily be reduced in a corresponding ratio. 



It is recognised, then, that the conditions under which 

 experiments are made in an artificial gallery are not quite 

 the same as those which obtain in a mine, and that the 

 results observed in the one case may be essentially different 

 in many respects from those experienced in the other. 

 Hence it arises, probably, that although experiments have 

 been assiduously carried on in artificial galleries for 

 several years, no distinct pronouncement has yet been made 

 as to the best means of either preventing or arresting 

 explosions. 



The Altofts gallery has been lent to a joint committee 

 consisting of the original committee of colliery owners and 



8 Cinquieme Sirie d'Essais sur les Inflamma ions de Poussieref, Aout, 

 igii, p. 68. 



NO. 2208, VOL. 88] 



members of the Roj-al Commission on Mines, which is 

 stated to be about to undertake further experiments ; M. 

 TafTanel, who conducts the experiments for the French 

 colliery owners, continues his experiments, and has 

 sketched out a programme for many more ; the .Austrian 

 investigators have made experiments with mixtures of 

 coal-dust and cement-dust, with watered zones, and with 

 what they designate water-curtains, which have not given 

 satisfactory results ; and, lastly, the experiments at the 

 Pittsburg gallery have been only of a preliminary character 

 so far as described up to the present, and have shed no 

 particular light on the subject. 



So far, then, no finality has yet been arrived at, and 

 all the investigators have intimated that they have many 

 more experiments still to carry out. But since these ex- 

 periments were begun, and since the dangerous nature of 

 coal-dust has been publicly demonstrated by their means, 

 two explosions, fit to take rank with the most disastrous 

 of last century, have occurred in this country, showing 

 that the demonstrations have been futile so far as stimu- 

 lating spontaneous action on the part of some managers 

 to take even ordinary precautions is concerned. Partly for 

 this reason, and partly because we may have to wait for 

 some years longer before the investigators arrive at a 

 unanimous decision as to what they think ought to be 

 done, it would perhaps be well in the meantime to adopt 

 a course that would undoubtedly have the effect of vastly 

 reducing, if not entirely eliminating, the risk of explosions, 

 both in damp and dry mines, by establishing three simple 

 rules of the following import : — 



(i) That in all dry mines the dust within the radius of a 

 shot-hole now specified by the Coal Mines .Act be damped 

 with sprinklers attached to a luater-main. (I am of 

 opinion that the distance of 20 yards from the shot-hole, 

 within which the dust is required to be watered accord- 

 ing to the existing law, is unnecessarily great, and that 

 with tlio short-flaming explosives and water-cartridges 

 now in use a distance of 10 yards is ample.) 



(2) That in all dry mines the dust be damped within 

 a certain minimum radius of every accumulation of in- 

 flammable gas, or place in which the air shows a cap 

 of one-quarter of an inch or upwards in height, by the 

 same means as those mentioned in the first case. 



{3) That all work be prohibited in both damp and dry 

 mines within a certain minimum radius of every accumula- 

 tion of inflammable gas, or place in which the air shows 

 a cap of more than one-quarter of an inch in height, 

 excepting only that required for the removal of the 

 accumulation, or foul air, respectively. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



BiRMiNGH.VM. — The Coal Owners' Associations of the 

 South Midland district, realising that rescue work in mint-s 

 is a subject in connection with which research is desirable, 

 h.ive arranged with the University for the appointment of a 

 lecturer in mine rescue work. The stipend of the lecturer 

 will be defrayed by the Coal Owners' Associations, the 

 amount offered being 250/. per annum. The functions of 

 the lecturer will be not only to give lectures and instruction 

 in the subject at the University, but also to be responsible 

 for the organisation of rescue work, and to superintend the 

 equipment and training of rescuers throughout the district. 



Mr. John Furneaux Jordan has been appointed Ingleby 

 lecturer for the current year. 



London. — The report of the Royal Commission on 

 University Education in London, recommending a central 

 building for the University, to which we referred in an 

 article published in Nature (January 4), has already pro- 

 duced an important scheme for the acquisition of a vacant 

 site of more than 100,000 square feet immediately behind 

 the extension of the British Museum. The site consists of 

 four plots, two on each side of the new British Museum 

 Avenue, on one of which it is proposed that a spacious 

 hall should be built for the University, the other three 

 plots being used for administration, library, small lecture 

 theatres, rooms for graduates, and headquarters of the 

 Officers Training Corps. The site is part of the Bedford 

 estate, and it is stated that the Duke of Bedford is pre- 



