j.\NUARY 12, 191 1] 



NATURE 



Zn 



apparently issued in defiance of all the dicta of science 

 and all the teachings of practical experience. All these 

 warnings are based on the assumption that a high 

 barometric pressure indicates a condition of danger 

 for the coal miner; for example, the warning pub- 

 lished on December 19 last states : — "While the glass 

 remains at about its highest level, miners are advised 

 :o beware of escapes of firedamp from the strata." 

 Ihe entire falsity of this assumption has been re- 

 peatedly pointed out in the technical press, but as the 

 warnings are still being issued on the same lines, it 

 nay be worth while to place the main data on the 

 -abject before those interested in the matter. 



Firedamp occurs occluded in coal, and also contained 

 under pressure in cavities and fissures in the coal 

 -eam itself and in the strata adjacent to it. Further- 

 ncM-e. in every collier}- there are larger or smaller areas 

 rem which the coal has been removed, and which are 

 nore or less loosely filled with debris, either deliber- 

 ately thrown or packed in to fill up partly the empty 

 spaces, or due to the breaking down of the roof of 

 the coal seam. Such a partially filled space is known 

 rechnically as the "goaf"; the ventilating current in 

 i colliery traverses the various roadways and work- 

 ings, passes along the working faces of the coal, and 

 may sweep along the edge of the goaf, but the goaf 

 itself is never ventilated. Hence in a fier\- colliery 

 the goaf gradually fills with a mixture of firedamp 

 ;nd air. The object of the ventilating air current is 

 o dilute the firedamp given off gradually from the 

 ;>al faces, or coming off more rapidly from cavities 

 nredamp escaping in this way being known as a 

 blower"), to such an extent as to produce a non- 

 xplosive atmosphere in all accessible parts of the 

 mine. 



A gas explosion can only occur in a properly 

 worked collier\- when an evolution of firedamp 

 takes place in excess of the normal, and the 

 question directly before us is how this rate of 

 volution of firedamp can be affected by changes of 

 tmospheric pressure. It is an obvious truism that 

 •ncrease of pressure nmst tend to prevent the escape 

 f firedamp from the coal or the strata of rock. In 

 vhe case of gas contained in cavities, this is often 

 under very great pressure, as high as 30 atmospheres 

 having been recorded by actual measurement, and 

 in such circumstances, even a considerable change 

 in the height of the barometer, say 3 inches, amount- 

 ing to only one-tenth of an atmosphere, would have 

 but little influence. On the other hand, blowers 

 sometimes give off gas at pressures not greatly above 

 that of the atmosphere, and then fluctuations of atmo- 

 -oheric pressure may have a decided effect. Thus in 

 ne Colliery Gitardian of December 13, 1907, Mr. 

 D. S. Thomas gives a record of his obser\'ations on a 

 blower extending over a twelvemonth, in which he 

 •und that the flow of gas from the blower increased 



- uite regularly whenever the barometer fell, so much 



- > that " the slightest change in barometric pressure 

 as shown more delicately than the barometer itself 



could record it." 



As regards occluded gas, it is quite certain that this 

 conies off more readily when the coal is placed under 

 diminished pressure. Numerous investigations have 

 been made on this point, and it has been found that 

 whilst a small reduction of pressure causes the 

 occluded gas to commence to come off, yet even after 

 many hours' exposure in a vacuum at ordinarv tem- 

 peratures, a considerable proportion of the gas is still 

 retained. As regards therefore the gas contained in 

 the coal and the surrounding rocks, it appears to be 

 beyond controversy that a low barometer must neces- 

 sarily correspond to a somewhat increased evolution 

 of firedamp. 



The gas contained in the goaf is under somewhat 

 NO. 2150, VOL. 85I 



different conditions; so long as the air in the airways 

 of the mine is under the same pressure as that in the 

 goaf, there is no tendency for the latter to flow into 

 the former once the condition of equilibrium has been 

 attained, whether this be under a regime of high or of 

 low barometric pressure. A rapid fall of the barometer 

 would necessarily affect the airways first, and would 

 therefore cause the foul air from the goaf to flow out 

 into the airways of the mine, and it is quite c<mi- 

 ceivable that a series of rapid alternations of high and 

 low pressure, bringing about a considerable inter- 

 change between the air in the roadways and in the 

 goaf, would promote diffusion, and thus help to in- 

 crease the proportion of firedamp in the airways; in 

 the main, however, it is the falling of the barometer 

 that will bring about this result. This reasoning, 

 based upon elementary- physical laws, appears to be 

 incontrovertible, and points conclusively to a falling 

 barometer as the condition to be dreaded, and that 

 this is the case is well known to all mining engineers, 

 and apparenth" to everycMie except the Press Associa- 

 tion. It seems probable that the firedamp of the goaf 

 plays a greater part in fouling the air of a mine than 

 does that evolved from the coal, as a general rule, and 

 that therefore a rapidly falling barometer is more 

 dangerous than a continuously low barometer in most 

 cases. 



Numerous observations have abundantl}^ con- 

 firmed this reasoning; the Prussian and Austrian 

 Firedamp Commission showed conclusively that the 

 f>ercentage of firedamp in the air of mines was greater 

 when the barometer fell, and the British Commission 

 of 1886 came to the same conclusion, though they 

 attached less importance to the subject; it may be 

 advisable to quote their words : — " While we recog- 

 nise that variations of atmospheric pressure exert 

 influence on the escape of gases which have accumu- 

 lated in the cavities, and possibly to a slight extent 

 on that of gases emitted directly from the coal, we 

 entertain great doubt as to the wisdom of placing 

 reliance on the issue of meteorological warnings." 



In addition to the work of the various commissions, 

 there are in existence numerous ref>orts of investiga- 

 tions carried on in this country- and on the Continent, 

 notably in Westphalia and the north of France, and 

 all agree in showing that an increase of firedamp in 

 the air of mines attends a fall of barometric pressure. 

 It is thus inexplicable why the Press Association should 

 still continue to look upon a high barometric pressure 

 as a source ol danger, unless on the reasoning that a 

 high barometer must fall before ven*- long, and it 

 may be charitably assumed that the warnings are 

 issued on this hypothesis. Nevertheless, the statement 

 of the recent Royal Commission on >Iines respecting 

 these warnings (second report of the Royal Commis- 

 sion on Mines, 1909, p. 175) : — " They are misleading, 

 and, as far as we can see. their publication serves no 

 useful purpose," deserves most emphatic endorsement. 



Seeing that a barometric change cannot, of course, 

 per se, bring about a colliery explosion, but can only 

 produce conditions under which an explosion is liable 

 to occur, the explosion itself being determined by the 

 coincidence of several more or less accidental circum- 

 stances, it is hardly to be expected that statistics of 

 explosions would be of anv great value. In order, 

 however, to get as much light as possible upon t^e 

 facts of the case, I tabulated some time ago all the 

 explosions that occurred in the year 190s, and com- 

 pared them with the state of the barometer at Kew; 

 parenthetically, I may remark that I took the Kew 

 readings because the news agency bases its warn- 

 ings upon it, although it is, of course, the state of the 

 local barometer and not of the Kew barometer that 

 reallv affects the question. The results were as fol- 

 lows : — 



