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35. There was complete agreement among all the mining engineers and other expert witnesses at the Inquiry as to the place of origin and cause of the explosion. Following upon careful investigations underground and their consideration of all relevant factors, such as signs of violence, direction of force, condition and position of bodies, nature of the work being done at the time and probable or possible sources of ignition in relation to the possibility of the presence of an inflammable or explosive atmosphere at the site of a suspected source of ignition, the expert witnesses were unanimous that

36. Having first satisfied myself that all other possible sources of ignition could be eliminated, I had no hesitation whatsoever in coming to the same conclusions.

(b) Other Possible Sources of Ignition

37. The other possible sources were: defective flame or electric safety lamps; electrically operated machinery, cables and switch-gear; compressed-air plant and accessories; signalling apparatus; magneto exploder; and frictional heating or sparking. Following a careful and expert examination of all these possibilities, the only potential source of ignition of an inflammable firedamp-air mixture discovered was a patched compressed-air hose which showed definite signs of burning at the patch. But since this piece of hose was lying on the floor near the face end of the mothergate in No. 2 Dip Face, it was inconceivable that it could have been in direct contact with an inflammable firedamp-air mixture at the time the explosion happened. It was therefore ruled out as a possibility in this explosion.

38. Nevertheless, as this potential igniting source is liable to be overlooked at collieries, I think it necessary and advisable to draw attention to this possible danger and to indicate how the danger arises. For examination and test, an 8-in. length of the 2-in, diameter hose containing the patched puncture, together with a piece of sacking folded to give four thicknesses, which was strapped over the puncture, were sent to the Ministry's Research Laboratories at Buxton. Examination of the wall of the hose at the puncture showed unmistakeable signs of burning of the cotton reinforcing, while one edge of the sacking also showed signs of burning. Further, the imprint of the patch could clearly be seen on the hose, while the recovered patch was about one inch shorter than the imprint. Presumably the remainder had been burnt away. Comparison with previous experiments indicated that this puncture had been a "squealing" leak and that the heating had been caused by internal friction. Further examination showed that the puncturing of the hose caused tearing of the inside surface, the tears radiating from the puncture and leaving tongues of rubber and reinforcement. It was concluded that the escape of air caused these to vibrate at a high frequency, giving rise to some heat due to friction at external rubbing surfaces, but even more due to internal friction of the tongues as they stretched and bent. It was suggested that the cotton reinforcing had then disintegrated and part of it scattered as sparks which were capable of igniting an inflammable firedamp-air mixture, or, if they fell on suitable combustible material, of starting a fire. There seemed little doubt in this case that they caused either the smouldering or burning of the sacking wrapper. Clearly, an improperly patched puncture in a compressed-air hose is a potential source of ignition and a positive danger if such hose is used in any part of a mine where it may be in contact with combustible matter or inflammable gases. I should add that attention has already been drawn to this danger in the Twenty-third Annual Report of the Safety in Mines Research Board (1944) and in a letter from Dr. H. F. Coward, the Director of Research, published in the "Colliery Guardian" and "Iron and Coal Trades Review", on 24th June, 1944.

(c) Operations on No. 2 Dip Face

39. Since it was abundantly clear from the evidence that no suspicion attached to any part of the mine other than the No. 2 Dip Face, it is necessary only to describe the work being done on this face immediately prior to the explosion in order to get a picture of what happened. There were no survivors from this face but, so far as could be ascertained, the work in progress on the face that afternoon included (i) the ripping and packing of the mothergate, (ii) the undercutting of the coal face, (iii) pipe-shifting on the right-side face, (iv) advancement of the face chocks and of the conveyors on both left-side and right-side faces, and (v) the advancement of the strip packs on both sides of the face using stone obtained from the waste. From the position of the bodies and the state of progress of the work up to the moment of the explosion, it is clear that the work had been proceeding at the normal rate, and that the job of pipe-shifting had been completed, for the fitters by this time had left the face. Since all the expert witnesses were agreed that the explosion originated with shot-firing, only this aspect of the work on this face need now be considered in detail.

(d) Shot-firing on No. 2 Dip Face

40. Investigation showed that eleven shots, charged with a sheathed permitted explosive, Polar Ajax, had been fired by deputy Murtagh on No. 2 Dip Face that afternoon, as follows

The order of firing was probably (a), (b) and (c). The shots under (b) and (c) were bored from the face towards the waste at an inclination varying from 20 to 25 degrees to the plane of roof, with the exception of one shot on the left-side face which had been bored from the waste towards the face. The holes were from 3 ft. 6 in. to 4 ft. long.

41. There was no evidence to throw suspicion on the shots fired in the mothergate or in the left-side face. The roof shots on the right-side face were almost certainly fired in the order 1, 2, 5, 4 and 3 (see Fig. 1). Some of the material from shots Nos. 1 and 2 had been packed. The positions of the partially coiled firing cable and of the exploder (Fig. 1) indicated that shot No. 3 was the last shot to be fired and that this was done only a short time before the explosion. The bodies of shot-firer Murtagh, and of Brannon, a chock-drawer, were found lying opposite this shot-hole. Both men died from carbon monoxide poisoning; but whereas Murtagh showed no sign of external injuries, Brannon had sustained a fractured skull and a severe neck laceration before death.

42. In explanation of this, Mr. G. D. Nussey, H.M. District Inspector of Mines, suggested that when Murtagh was ready to fire shot No. 3, he sent Brannon down the face to prevent anyone approaching the shot from the direction of the right tail-gate while he went up towards the mothergate to fire the shot and guard the approach from that side; that when the shot was fired Brannon was struck by a stone projected from the shot and had then immediately moved towards Murtagh who, having lust detached the cable from the exploder (and probably also heard a shout from Brannon) moved down towards him; and that when they met nearly opposite the shot-hole, the explosion happened. Another explanation suggested was that immediately the shot was fired, both men saw some indication of flame, that both made towards the shot-hole to see what had happened, that when they met near the hole the explosion occurred and that Brannon was then struck by some missile projected by the explosion. But whatever the sequence of events, it is clear that there must have been a short interval of time between the firing of shot No. 3 and the actual explosion.

(e) Detailed Examination of Shot-holes

43. Careful examination revealed no dangerous features associated with shot-holes 1, 2 and 5. These shots were therefore ruled out as possible causes of delayed ignition. Observations made with regard to shot-holes 3 and 4 make it desirable to describe each in some detail.

44. The conditions of shot-hole No. 4, as noted by Drs. Grimshaw, Shepherd and Phillips of the Ministry's Safety in Mines Research Branch on 1st September, are illustrated in Fig. 2. An almost continuous trace, AB of the upper surface of the hole was left on the roof for a distance of about 3 ft. 6 in. At CE a further trace of about 6 in. of the lower surface was observed on a ledge of roof bordering a cavity in a shatter zone caused by the shot. Starting at a point about 5 in. from B and going towards A, there were indications of clay stemming. From this it was assumed that the remaining 11 in. of hole contained the explosive. This length represented two 4 oz. cartridges. The explosive, clearly, had not expended its full energy in breaking down the roof bed, but had partly expended itself in producing the shattering observed beyond the above points B and C, resulting in a cavity extending upwards to the coal bed above the immediate shale root.

45. It was estimated that there was about 2 in. of shale between the end of the shot-hole as bored and the immediate roof bed. There was also a pronounced opening along the bedding plane between the shale roof and the coal above- a condition that almost certainly existed when the shot was fired, for otherwise it would be difficult to explain the upward shattering effect. There is no reason to suppose that the 2 in. thickness of shale between the end of the hole and the bed separation cavity was broken before the shot. Experimental work at the Buxton Research Station has indicated that when a charge is fired in a hole which runs towards an opening containing an inflammable mixture of firedamp and air, a barrier of 2 in. of solid material (e.g. of stone or a plug of clay) renders ignition very improbable. The proximity of the hole to the parting above, therefore, constituted the only possibly dangerous feature of this shot. A sample of the atmosphere at point S1, taken through a metal tube inserted for a distance of 2 ft. 6 in. into the bed separation cavity showed on analyses: 71 .7 per cent. Methane; 7.05 per cent. Carbon Dioxide and 3.67 per cent. Oxygen.

46. The conditions noted by the same three observers at shot-hole No. 3 are illustrated in Fig. 3. This hole was bored immediately over a prop and the length AB was left more or less intact and partly filled with loose stones. The firing of the shot had brought down the roof bed along the line of the hole between B and C and there was a 6-in, socket at the inner end. It is, therefore, highly probable that the explosive was not inserted to the end of the shot-hole but only as far as the point C, where there was a vertical roof fracture or cutter-break parallel with the face. As shown in the diagram, this break was closed laterally except for a small vertical pocket which crossed the hole, and it was found to extend upwards for about 3 in., where it was crossed by a horizontal parting. at least ½ in. wide, between the shale and coal beds. It is most unlikely that the vertical pocket was open to this extent before the shot was fired and it seems likely that it was partly filled with rock fragments which dropped away after the shot was fired. It is possible that the cross-section of the shot-hole was reduced at C by one of these fragments. Alternatively, there may have been a slight displacement across the vertical fracture at C, sufficient to disturb the continuity of the hole and thus prevent the charge from being pushed home.

47. In addition there was extensive bed separation between the shale and the coal. When obtaining gas samples in the vicinity of the shot-hole, it was found possible easily to push the metal tube-1/8 in. in diameter- through an opening at the back of the socket for a distance of at least 6 ft. The loudness of the noise made by the buried end of the tube during movement made it evident that this extended opening was horizontal and not far above the ripped surface of the roof bed. The experience of the investigators led them to conclude that this opening was present when the shot was fired. Measurements clearly showed that the back of the hole was drilled to within a very short distance-possibly to within in. at the nearest point-of the plane of bed separation, although at the time of the examination there was easy access through a thin layer of broken shale. It, therefore, remains a distinct possibility that this access existed at the moment of firing. The thrust of the drill could quite easily have broken the thin crust of shale for it must be remembered that the action of the shot itself did not produce any marked shattering of the socket.

48. Two other features peculiar to shot-hole No. 3 were also observed. On the ripped surface of the roof bed in the waste there were pronounced cleat planes. Along one, about 8 in. to the left of the shot-hole, there was an opening of about ¼ in. which extended to the bed separation cavity above the roof bed. There was another cleat plane 1 in. to the right of the shot-hole and, although this was not nearly so open, it was nevertheless a plane of weakness which would facilitate a local displacement of the roof and reduce the strength of the shale at the end of the shot-hole. This cleat formed one end of the vertical pocket located at C. Moreover, on the right-hand side (looking towards the waste) of the ripped portion of the roof, there was a detached piece of the roof bed bounded by an open break DEF, Fig. 3, which extended laterally over the waste. The projected extension of this break towards the shot-hole would cross the hole almost tangentially at a point near the explosive charge if, as is likely, the hole was blocked or obstructed at the vertical fracture already described.

49. Three gas samples, S2, S3 and S4, were obtained near shot-hole No. 3. The position in which they were taken and their analyses are as follows

			Carbon
	Position	Methane	Dioxide	Oxygen
		per cent.	per cent.	per cent.
S2.	At top of vertical pocket	88.4	7.42	0.89
S3.	Five feet into break developed towards right-hand waste	1.91	0.12	20.39
S4.	Six feet in bed-separation cavity along direction of shot-hole	5.03	0.49	19.57

The presence of the open cleat no doubt accounts for the lower percentage of methane in the sample taken some distance in the bed-separation cavity, but it is significant that the atmosphere here was inflammable and capable of self-propagation of flame at a slow speed.

50. From these considerations, I think there can be little doubt that the firing of shot No. 3 originated the explosion. Moreover, the circumstances were such that the firing of the shot was likely to result in an ignition of firedamp in the bed-separation cavity between the shale and the overlying coal, the flame of which would travel slowly and unobserved along narrow openings until it encountered a larger volume of firedamp and air in the waste, thus giving the delay indicated by the factual evidence, between the firing of the shot and the development of the main explosion.