Analyses of samples of air taken in the place by Mr. John Cadman are given in Appendix I. along with other samples from the seam.

These samples were taken with the air not carried forward to the working faces as before the explosion, and the results obtained there could not be taken as indicating the state of matters before the explosion, but they showed that fire-damp was issuing into the workings somewhat freely, and that the air at the face of the working places beyond the brattice might easily have contained some appreciable proportion with the ventilation in full swing.

Although it appeared probable from the first that the shot was the point of origin of the explosion, any other possible cause was carefully looked for and no other probable point of origin could be ascertained except the flame of some one of the safety lamps in u se. All the lamps which were in use within the area in which the explosion undoubtedly originated were found to be intact after the explosion, with the exception of Madden's lamp, No. 10, the glass of which was gone and the poles bent, and there was a dent on the bottom of the oil vessel as though it had fallen on to the pavement, which in the lampman's opinion had probably caused the damage. These lamps along with the other lamps in the seam, some of which were damaged by the explosion, are tabulated in Appendix III. Through the kindness of Mr. Philip Kirkup they were tested in the presence of Mr. A. D. Nicholson and Mr. Ford at Urpeth Colliery, where there is a testing arrangement consisting of a small chamber into which the lighted lamp is placed and an inflammable mixture of lighting gas and air driven past it at a considerable velocity by a small steam driven fan. The lamps tested were all extinguished without allowing flame to pass in from four to six seconds. The lamps used by No. 10 in the list (Madden) by No. 13 (Oswald) and a spare lamp found at the shaft, the last two of which had been exposed to the explosion after it had attained considerable force, were damaged as set out in the table and were not tested. The lamp used by No. 9 (Rollin) had not been found, and, as already stated, was probably under a fall of stone at the point where his body lay.

An examination of some features of the explosion will help to determine the relative influence of fire-damp and coal dust in its extension.

There were some marked exceptions to the passage of the explosion —

(1) This road, as already stated, was the intake airway, and according to the usual experience in extensive explosions was the road along which the explosion might have been expected to extend with the greatest violence. It was the passage in the seam where the air would almost certainly contain the least proportion of fire-damp, but had the ordinary practice been followed of waking it also the main haulage road it would have contained most coal dust; as it was only used as an intake airway and only acted as a subsidiary haulage road for the coal worked in driving it and then only beyond the last connection with the centre winning, it did not contain more coal dust than an ordinary road, and this dust had been much obscured by the shooting down of 16 inches of stone from the roof over its entire length. The sample D 11, Appendix II., taken from the floor of this road at the point marked on the 4-chain plan it will be noted contains 62.8 per cent. of ash, the highest percentage in any of the specimens given in the table.

There might very well have been a deposit of the fine upper coal dust from the screens on the surface and the tubs while being raised in the downcast shaft on this road, which was, however, absent probably due to these reasons —

(2) The absence of evidence of explosion at the faces of nearly all the culs-de-sac, tabulated in Appendix IV., was as well marked here as in the case of the explosion at Urpeth Colliery on the 17th December, 1906, in the report on which the same question was discussed.

The numbers of the culs-de-sac in Appendix IV. correspond to the numbers on the small scale plan, Fig. 2, on Plate I.

Such of the brattice as was left standing was in most cases that next the face, and the timber and exposed surfaces there were clean and undusted. The flame of the explosion had gone so far into them as evidenced by the coked dust deposited and brattice cloth burned, but had died out before reaching the face. Considerable compression of air had taken place in them, there were several examples noted of brattice cloth, torn down by the explosion at or near their entrances and probably carried so far into them, was found caught against props or projecting stones by a rush of air which had clearly come from the face.

If we exclude coal dust from consideration and confine our attention solely to fire-damp as the inflammable agent in the extension of the explosion, what reason can be given for the phenomenon ?

The air current would reach the end of the brattice, of the places that were bratticed, on one side and return on the other and carry any fire-damp already in it nearly to the face, as well as receiving its quota on arriving there, and beyond the brattice out of the air current there would certainly be a still greater percentage present in the air. In the places not bratticed there would probably be most fire-damp in the air next the face.

At the moment of the explosion there would be considerable compression of air in the culs-de-sac as it had no escape, but this compression of the air would rather promote than check combustion of fire-damp and air.

A reason that might be suggested, limiting consideration to fire-damp alone, would be that there was too much fire-damp present to allow of combustion, or more than 16 per cent., but this is not a tenable suggestion; even if some sudden issues had occurred they could hardly have taken place at the face of all the culs-de-sac at the same time, and we can scarcely conceive the men on the inbye side of the place in which the shot was fired working calmly in an atmosphere so charged with fire-damp that the passage of flame would not be possible in it. Their lamps would have refused to burn had such a condition prevailed. This explanation must be rejected, and the extension of the explosion becomes inexplicable on the assumption that it was caused by fire-damp alone.

If we include coal dust as one and probably the principal combustible agent in the extension of the explosion, an explanation not unreasonable can be given, and it is the same as was given in the case of the Urpeth explosion, namely, that the rush of air preceding the explosion and necessary to raise the dust would become less and less as the faces of the culs-de-sac were approached, and would be replaced by compression, and consequently the dust was not raised from the floor and no cloud was formed into which flame could pass; that this had been the case was evident from the clean undusted appearance of these places next to the face, although there was sufficient dust on the floor mixed with coarser particles to have caused a dusting of the surfaces had it been raised.

A second reason that might be advanced is that there is in some cases less dust as the face is approached, and if the seam is making any water, more moisture, but in the present case there was dust on the floor right up to the faces.

(3) The escape of the dip workings was no doubt due to the absence of dust near the shafts owing to moisture there.

The only roads leading to these workings which were open were the two roads crossing the shafts, and they were both damp. Even had the flame been able to extend far past the shafts the dip workings themselves contained much less dust than those to the rise and probably not sufficient in quantity to have propagated an explosion.

There were three districts in the seam ventilated by separate air currents (1) the main current to the south-east; (2) the scales ventilating the dip workings ; and (3) the air descending the stone drift and ventilating the workings north and west of the shafts. The explosion extended with force and flame over two of the districts (1) and (3), but missed out the third (2).

It is difficult to suppose that the air in the two districts traversed was in an explosive condition from the presence of fire-damp ; two separate issues would be necessary or a general slackening of the ventilation, of neither of which was there any evidence whatever.

All the victims were in the dress they usually wore while working, and their discarded garments hung near.

There was no evidence that any of them had been under any alarm up to the moment of the explosion, but had been pursuing their ordinary work, and although this fact in this case does not offer so marked an example as some other explosions have afforded, it is somewhat difficult to come to any other conclusion than that they were working in an area containing at the time the elements of explosion, and that the combustible element could not be fire-damp alone, otherwise they would have observed it on the flame of their safety lamps and been retreating.

There is no reason to suppose that the ventilation was not as usual, or that any abnormal issue of fire-damp had taken place, and it appears that Ashman had been making his round, firing shots, and had already fired six before he arrived at Cowen's place, viz., one shot in the top canch in the left winning, two in the top canch in the centre main winning, one in the coal in Clarke's stenton, one in the bottom canch in the right main winning, and one in the bottom canch in the place next it to the right. The shot in Cowen's place was probably ready to fire, and it is to be presumed that, after charging and stemming the hole, Ashman made the usual examination as regards the presence of fire-damp. The battery was coupled up and they both retired to where it and their lamps were found. The current was turned on and the shot exploded, and apparently Ashman had had time to disconnect the wires from the battery before the explosion came over them. The shot appears to have dislodged all the stemming as well as lifting the stone, and there would be a rush of highly heated gases from it along the floor, which would disturb the debris in the cut, and some fine coal and stone dust would be thrown into the air from here, as well as coal dust lying on the canch directly over the shot hole.

Both the coal dust and stone dust may, at the initiation of the explosion, have simply acted as finely divided solids in determining the ignition of a mixture of fire-damp and air not inflammable per se in the manner demonstrated by the late Sir F. Abel.

What amount of fire-damp was present in the air must be conjectural, probably there would be from 1 to 2 per cent. in the air reaching the end of the brattice and something more in the still air beyond ; the combination of air, gas, and dust had been an inflammable mixture and it was ignited by flame from the shot causing a disturbance which raised more dust into the slightly polluted air current, and the explosion now fully established, and raising dust in dense clouds before it, travelled over the parts of the seam affected, and into two separate splits of air. The flame probably came on to the main road by the stenton directly opposite Cowen's place, and would be seen entering by Chivers, Errington, and Madden, who were on the main road just inbye, and this probably accounts for their bodies being found inbye of the points where they would be at the moment of the explosion.

Ashman had been a deputy and shot firer in the Glebe Pit since October 1907, and he had acted in a similar capacity for some years in Houghton Colliery, a fiery and dusty mine a few miles distant; there are no grounds for suggesting that he did not make an examination for gas before firing the shot and with the only means at his disposal, the flame of the safety lamp, which even when reduced to its smallest amount will only indicate about 2 per cent. of fire-damp, there might yet be sufficient fire-damp in the air in conjunction with the coal dust raised by the shot to form an inflammable mixture, as so long ago as 1876 Professor Galloway proved experimentally that "*a mixture of fire-damp and air, in the proportion of one volume of the former to 112 of the latter, becomes inflammable at ordinary pressure and temperature, when charged with fine dry coal dust, such as that which is to be found on the roadways in dry coal mines."

A somewhat undue importance was in my opinion attached by some of the expert witnesses at the inquest to the shot being overcharged, and the point was emphasised by the verdict of the jury; it is true that the line of the hole corresponded with an ordinary horizontal parting in the stone, and consequently the explosive had less work to do than it would have had, had this not been the case, and it is also clear that if the stone above the parting was readily lifted the pressure on the stemming would be relieved and it would easily be blown from the hole.

On the other hand, the stoneman and deputy were experienced men and would not probably introduce more explosive than they thought necessary, although it may be pointed out that the minimum weight of the cartridges was 8 ozs.

I do not think there was anything specially abnormal about the shot, many shots are fired under similar conditions and with similar results so far as the displacing of the stemming is concerned, and if the margin of safety is passed in the case of such shots conditions of extreme danger must often arise.

The fact that the explosion took place under conditions which cannot be described as abnormal and which may often arise in dusty and gaseous collieries is disquieting.

* Transactions of the Royal Society, vol. XXIV., page 366.