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IV. CAUSE OF THE EXPLOSION
The explosion was primarily one of firedamp. The deceased officials and workmen went into the district with the intention of clearing an accumulation reported by the nightshift deputy to exist in Nos. 2 and 3 headings and which he had only partially succeeded in moving, and it is reasonable to conclude that the explosion occurred while they were thus engaged. There was general agreement among the inspectors, management and Mr. Price (called as an expert by the owners) that the point of origin was within an area extending from half-way between No. 5 and No. 4 left thirl in No. 3 heading, outbye down to and including No. 4 left thirl and No. 5 right thirl, but excluding No. 2 heading. This suggested area was extended slightly as between one witness and another, but that indicated was common ground, and I am myself satisfied the explosion originated somewhere in this vicinity.
The point at which an explosion commences frequently represents a quiescent spot with little or no evidence of force, the violence becoming evident as the explosion gathers momentum and is met by obstruction.
But while witnesses said where they considered the starting point was, and also the course which the explosion subsequently followed, no one felt able to express any definite opinion as to the cause of ignition. It therefore becomes necessary to examine the various possibilities. What then were the possible sources of ignition within the area described ? They were : – electricity, shotfiring, electric cap lamps and flame safety lamps.
Electricity – Mr. Frederick Thomas Hindley, one of H.M. Electrical Inspectors of Mines who made a detailed examination of the electrical plant after the explosion, and Mr. Joseph Pattinson the chief electrician at the colliery who accompanied him on these examinations, both gave evidence of certain defects found to which reference must now be made.
(a) The first were in a bank of three panels, Nos. 13, 14 and 15 at No. 4 left thirl. Two of these panels controlled the No. 2 fan and the coal cutter in the chain conveyor area, and the third one, No. 15, controlled the drilling machine in the same area – No. 5 right. Nos. 13 and 14 were G.A.1 contactor panels and the bus-bar chambers communicated one with the other. No. 15 was a MU.10 drill unit and a bus-bar end plate formed the connection between panels 14 and 15. There was therefore a continuous bus-bar chamber for 13 and 14, but a barrier between that and No. 15 so that No. 15 can be left out of further account.
Examination showed that a loose incoming connection to the rear bus-bar in panel 13 had given rise, at some time, to considerable heating and arcing at this point; solder from the cable lug had melted and splashed on the bottom of the chamber, and some fusion had occurred at the poor contact between the lug and bus-bar. Given sufficient load, or any vibration such as might be caused by the opening or closing of the contactor below, sparking would very probably occur at this faulty connection.
The outgoing 100 amp. B.S. socket on No. 14 panel had at some time been replaced by one of another make and, owing to the difference in the fixing centres, could only be attached by one set stud instead of four. This did not form a flameproof joint between the base of the socket and the socket adaptor, and provided a path from the 13 and 14 bus-bar chambers to the external atmosphere. The socket which had been attached to No. 14 was found some little distance from the panel, having apparently been blown off by the explosion. The top left hand corner had been badly bent as if the socket had been lifted upwards against the stud to which it was secured, and the flange of the adaptor was also slightly bent at the corresponding corner. When the socket was put back on the adaptor and bolted up with one bolt there was an opening at the lower end of the flange of almost a quarter of an inch.
These two panels were brought to the surface and sent to the S.M.R.B. Testing Station at Buxton for official testing, which was carried out in the presence of representatives of the various parties. The tests carried out and the results were thus described by Mr. Rainford :–
The apparatus I received at the testing station, comprised two gate-end switch units coupled together such that the two bus-bar chambers formed a continuous chamber with a flit-plug mounting adaptor at one end and a blanking cover at the other end. Each unit was fitted with a marking plate with the inscriptions Reyrolle-Hebburn, Type GA1/XI, the FLP. crown mark and the reference number FLP. 1406.
Q. Does that mean it was flameproof?
A. That means it was a certified flameproof design under that certified number.
THE WITNESS (continuing): The main enclosures were in accordance with the certified design except that the "start" and "stop" push buttons were inoperative. The double bus-bar chamber, formed by the two single chambers bolted together at a centre flanged joint, was in accordance with the certified design. The outgoing cable attachment at the rear of Item No. 13 bus-bar chamber, comprising an angle adaptor fitted with FLP. 1455 B.S. socket, was in accordance with the certified design. A similar angle adaptor was mounted at the rear of the No. 14 bus-bar chamber and that was in accordance with the certified design, but the adaptor was fitted with a B.S. plug socket marked FLP. 1319, the socket of which is not designed to suit the facing of the adaptor. With reference to that the difference between bolt centres of the adaptor and the socket base would permit of only one fixing bolt being used as received at the testing station. This socket had a flange which was bent outwards at one corner where the one fixing bolt was fitted, so that when the bolt was screwed home the socket canted to one side. This prevented the socket spigot from engaging fully with the bore of the adaptor facing and at one side the socket flange joint was also left open with a gap of a quarter inch approximately.
The last point recorded is that the removal of the top covers from the bus-bar chambers revealed a loose connection in Unit No. 13, between the outer bus-bar and the connecting lug on the end of one of the incoming cable tails, and there was evidence of heating and possibly sparking at this point.
We prepared the double bus-bar chamber for test as regards flameproof enclosure by drilling and tapping the top access covers for the purpose of introducing an inflammable mixture of firedamp and air and also for the purpose of applying an ignition plug. We made a series of three tests; no ignition of an external inflammable mixture was obtained with ignition of an internal inflammable mixture effected at a point adjacent to the faulty bus-bar connection referred to above, this ignition point being remote from the open socket joint referred to. The damaged socket component was then replaced by a new socket of the same design, secured by the one bolt as before. The ignition point inside the chamber was not altered, and no ignition of an external inflammable atmosphere was obtained in a further series of three tests. The original socket with the bent flange was then replaced, so as to reproduce the open flange joint as before, but the ignition point inside the chamber was transferred to the other end of the chamber adjacent to the adaptor on which the socket was mounted. Under these conditions of test, ignition of the external inflammable atmosphere was obtained on the first test applied.
That briefly covers the tests which were made.
Q. Those are tests made with the ignition point at No. 13 panel corresponding to where you found there had been certain evidence of flashing?
A. Yes.
Q. And the communicating point, if I may so put it, at the flange you referred to in No. 14 box. Now can you tell us what distance there would be between the point of ignition and the point at which communication could be made with the outside atmosphere?
A. Approximately 24 or 25 inches, that is through the double bus-bar chamber round through the elbow adaptor to the base of the socket.
Q. In other words you have a point of ignition in No. 13 box and the point of communication with the outside atmosphere in No. 14 box and the distance between those two points is roughly two feet
A. Yes. In other words the ignition point was remote from the opening.
Q. You made three tests, Mr. Rainford, and in no case did you get ignition? You have had a lot of experience in tests of this kind. You would attach importance to the fact of this two feet distance between the igniting point and the communicating point of the outside atmosphere?
A. It has been proved by experiment on a number of instances that ignition remote from an opening in such a way can reproduce conditions of flame propagation which would not allow flame to pass out of the opening.
Q. Only three tests were made, Mr. Rainford. Would you have expected if you had carried on for another three or six tests to have got an ignition?
A. No. Those tests were based on a wide range of experiments and we are able to limit such tests to a few which impose the most severe conditions. We made the most incendive mixture of the internal and the most easily ignitable mixture for the external mixture.
Q. You yourself were quite satisfied that it was not possible to cause an explosion under these conditions of test?
A. Under those conditions as reproduced for the test.
Q. Now you did, I think, carry out a test with the point of ignition a little closer to the opening?
A. Yes, mainly for our own information. We have to take the opportunity of these circumstances to build up our own experience of data, and for this purpose we transferred the point of ignition from the remote end of the bus-bars to the other end of the bus-bars which are adjacent to the elbow adaptor. On the first test we obtained an ignition made under those conditions of the external atmosphere.
By Mr. Harvey –
Q. One of the first points you found in examining the apparatus was that the start and stop push-buttons were inoperative. Can you tell us for what reason?
A. After we completed the tests we took off the main access covers and we found they were stuck in position by dirt.
Q. It was not that the electrical apparatus was inoperative?
A. No, it was a mechanical defect of the push-buttons.
Q. Was that due to the explosion in your view or was it likely to be a condition that obtained before the explosion?
A. From the condition of the push-button spindles I should say it was a condition before the explosion.
Q. You did in effect carry out six tests with the apparatus?
A. Two series of three.
Q. The first three tests, I understand, were made with the apparatus in the condition in which it was found after the explosion, that applies both to the socket and the adaptor, the socket with the bent corner?
A. I am working on information received at the time. I did not see the apparatus in the pit.
Q. In the first three tests the socket with the bent corner was used for that purpose in that bent condition
A. Yes.
Q. Is it not a fact the face flange of the adaptor was also slightly bent at that corner
A. It was slightly bent.
Q. And in the second three tests the new adaptor socket flange was flat and the adaptor flange was also flattened with the hammer before the tests were carried out ?
A. That is so.
Q. In your opinion were the conditions of the first three tests as likely to produce an explosion as you could make them in the circumstances?
A. Yes, definitely.
The defect thus disclosed is very disquieting and ought not to have existed, but on the result of the tests described, this panel cannot be held to be responsible for the explosion.
(b) Another defect was discovered at the No. 3 fan. Here a piece of 26 s.w.g. wire was found looped round the base of the pilot terminal in the fan cable socket, with the ends brought out between the bore of the socket and the plug body. This wire formed part of the electrical interlock circuit, the proper connection between the pilot terminal and the motor casing having been omitted.
It was considered that if this wire were making only poor or intermittent contact, particularly if this was towards the outer end of the socket and the interlock circuit was not intrinsically safe, then any sparking between the wire and socket or plug might have been incendive.
This apparatus also was sent to Buxton and submitted to test with the result given in evidence by Mr. Henry Robinson, a Scientific Officer of the Safety m Mines Research Board :–
I received an Aerex fan, to which was coupled by belting a 10 h.p. induction motor made by Metropolitan Vickers. The motor name plate bore an inscription FLP103, Group 1, with the serial number of the motor. There was also a gate-end panel which was marked 18 in chalk, made by Reyrolle, Hebburn-on-Tyne. That carried the FLP certificate No. 1406 for Groups 1 and 2, together with the identification number A. 688. I also received one length of trailing cable complete with two plugs, one marked No. 2, which married with the socket on the 10 h.p. motor, and the other marked No. 1, which married with the socket on the gate-end panel.
I was informed by the Electrical Inspector that the electrical circuit had been completed in the pit by the use of a piece of 26’S gauge wire, in a manner which has no doubt been described to you already. I therefore made my own connection in the same way and attempted to start up the fan by operating the push button on the gate-end box. I found that although the fan would start up it would only continue to run so long as that push button was kept depressed by hand. In order that the fan should run continuously that push button had to be kept spragged down by a wedge or some similar device. If pressure was removed from the push-button the fan stopped immediately, and throughout the whole of my tests I had to adopt that expedient in order to get the fan to run.
I opened up the gate-end panel to find out what was the cause of this defect and found that one of the leads which runs from the terminal of the push button to the No. 4 contactor was broken. The result was that, when the pilot circuit was completed and the contactors were closed, No. 4 contactor failed to short-circuit the push button switch, and hence as soon as the push button switch was released the circuit was broken and the motor stopped.
Q. Could you form any opinion as to whether that was a defect which had been continuing?
A. No, none whatever. It was just a clean break in a piece of wire at a point where it is normally anchored underneath a terminal screw.
Q. And when that break was made of course you cannot say, nor form any opinion?
A. No, sir it is quite impossible for me to say. Having got the equipment into a state where I could get the fan to run, I examined the fan first of all to see whether there were any signs of friction between the blades of the rotor and the casing of the fan. I found that the rotor ran smoothly in the casing without contacting the sides, and I observed the fan running for a long period in a dark room at its rated speed, and I could find no evidence of sparking caused by friction between the rotor and the casing. I did not proceed any further with that test. I was satisfied that if an ignition of gas had occurred it had not occurred as a result of frictional sparking.
I then proceeded to assemble the plug to the socket, using a piece of 26’s gauge wire on a number of occasions. I found invariably that if I used a piece of new wire the motor ran perfectly and I could get no sparks whatever between the outbye end of that piece of wire and the earthed plug or socket, showing that a very good contact had been made. After each trial I stripped the plug from the socket, removed the piece of wire for examination and found that it had been flattened over the length where it was trapped between the plug and the socket. That is a length of about one and a half inches. It had been flattened from its original thickness of about eighteen thousandths variously down to sixteen thousandths and eleven thousandths, showing that the gap between the plug and the socket was something in the order of sixteen thousandths to eleven thousandths of an inch wide.
There was clear evidence on the surface of the wire of where it had been trapped, and I have no doubt whatever that a perfectly good contact was made providing that the wire was only used once. In the course of my trials I used one and the same piece of wire on four successive occasions and found that it became progressively thinned by being trapped, and eventually in its minimum thickness was only about eight thousandths of an inch.
I wished to try the effect of using a piece of dirty or oxidised wire, but not having any available I decided to use a piece of wire which was coated with enamel. I removed the enamel from that part of the wire which was anchored round the pilot pin in order to get a good contact there, and then brought the remainder of the wire out through the gap between the plug and the socket in the usual way, but the wire that I used was only twelve and a half thousandths of an inch thick; that is to say, a thickness which was approximately the same as the thickness of the 26’s gauge wire which had already been squeezed down in my earlier experiments. Under those conditions I found that it was not a difficult matter to dispose the plug in the socket in such a way that I could get any one of three separate effects. I could get a very good contact between the plug and socket and the wire mutually so that the motor ran quite normally, and I could not get any sparking whatever from the outbye end of the wire. On the other hand, sometimes I could get no contact at all. The motor would not then start up although the switches had been closed. Now under those conditions I could get sparking repeatedly from the outbye end of the wire, and with that sparking I ignited gas on quite a number of occasions. I could also get a third state of affairs where the wire was making only a poor contact between the plug and the socket. The contact was good enough to allow the pilot circuit to close the relays, and hence for the motor to run, but it was not good enough to keep the wire at earth potential, with the result that when I stroked the plug with the outbye end of that wire I could get sparks from it again – not so vivid as they were before, but even with those less vivid sparks, after continued trial I did succeed in igniting firedamp on four occasions.
The tests that I have described, sir, were carried out prior to a visit which was paid to the Research Station by Mr. Harvey and Mr. Young and the various other people, and on the occasion of their visit I attempted to repeat all these tests. The tests were all repeated in their presence, with the sole exception of the test where I attempted to get no contact, so that the motor would not start up; the tests under which, as I said, I could get repeated ignitions of gas.
Q. That is Test 2?
A. Yes. I was not able to repeat that in its entirety. I was able to dispose the plug in the socket in such a way that the motor would not start up, but as soon as I got hold of the outbye end of the wire to stroke it across the earthed plug the act of touching the wire completed the contact somewhere inside and started up the motor, so that I could not show that test in its entirety. What I did, however, was to demonstrate in this way, that by taking the plug out of the socket I was able to show that any sparks which could be drawn from the pilot circuit were certainty capable of igniting gas.
Mr. Hindley produced on that occasion the identical piece of wire which had been removed from the plug and socket assembly in the pit. That piece of wire I found to be extremely dirty, almost black with corrosion and oxidation, and in the state that it was, it approximated, I assert, to the enamelled wire that I was myself using. When that identical piece of wire was assembled again to the plug and socket the motor ran quite satisfactorily, but we could not get sparks from the outbye end of the wire when we stroked it against the earthed plug. The most that we could do, by moving the plug in the socket whilst the wire was in position and watching the contactors in the gate-end panel, was to notice that on three or four occasions those contactors came out, showing that the pilot circuit was being broken even with the piece of wire which was used in the pit, but I could not synchronise my attempts to stroke that wire across the earthed plug with the attempts which I was making at the same time, by moving the plug about, to break the circuit somewhere further up.
That, sir, is the extent of the tests which I carried out.
Q. Now with this actual wire which was later produced what condition would you have required to produce sparking?
A. You would require conditions under which the wire was not making a very good contact with the plug and socket, or was making no contact at all. Under either of those conditions you could draw sparks from the outbye end of the wire which are capable of igniting gas.
Q. You say you could draw sparks?
A. Yes, by bringing the wire into contact with an earth you would have got a shower of sparks.
Q. You have referred to the wire in your earlier tests being reduced in thickness by being trapped, and the progressive reduction increased the risk, I take it?
A. Yes.
Q. Had this wire you received, the actual piece of wire, been reduced?
A. Yes, I measured that in what appeared to me at the time to be about its thinnest place and it was down in thickness to about ten thousandths of an inch. That was its condition after it had been used again by me in my tests at Buxton.
Q. So that that would correspond in section to the worst condition which you produced in your tests?
A. Yes, I attempted to reproduce those conditions by choosing the right diameter of wire for my tests.
Q. And as you saw the actual wire and the condition of the apparatus what would be your opinion as to the possibility of that having ignited firedamp?
A. Well sir, I should not put it higher than this, that there is a remote possibility that you could have the conditions all such at one and the same time as to make an ignition possible, but I would like to say that the chances of getting such an ignition are very considerably increased by the defect in the gate-end panel. If it were the fact in the pit that that gate-end panel had had to have its push-button switch kept depressed by means of a sprag, then any dangers which there might be in the pilot circuit are very vastly increased by the adoption of that practice. In fact, to do that is to throw away one of the most valuable safety precautions in that gate-end panel. May I go further, sir ?
Q. Yes, do. It is an important point and I want you to make it.
A. The point is this, that if that gate-end panel were in perfect working order and this push-button switch did not need to be depressed, then if you got a break in the pilot circuit, say at the motor end of the trailing cable, immediately you got a break there the push button switch would fly out, and from then onwards the whole of the line would be dead ; there would be no energy there.
Q. It would break the circuit?
A. It would break the circuit completely. If, on the other hand, you kept the push-button switch on the panel held down permanently by means of a wedge or a sprag, then for every contact which you make at the remote end of the trailing cable, each contact will give its own electric spark. To go further, if therefore at the remote end of the trailing cable you imagine intermittent contacts, repeated contacts, if the gate-end box is in perfect order only the first one of those contacts will give a spark and the remainder will give no sparks, but if you have a push button switch spragged down every individual break will give its own spark, and that is why it very considerably increases the possibility of getting dangerous sparking.
Q. So the lesson to be learned from that is that push buttons should not be spragged in position?
A. Most certainly.
They should work in their proper way, as they were intended to work.
By Commissioner –
Mr. Harvey, is there any thing you would like to elucidate?
By Mr. Harvey –
Q. Referring to this broken connection inside the gate-end box, bearing in mind the fact that the apparatus was conveyed from Harrington Colliery to the Testing Station at Buxton on a lorry under conditions of difficulty, over bad roads, do you consider that it is possible that the wire was broken away from the terminal in transit
A. I think it is a very definite possibility.
Q. I take it that you obtained the sparking between the wire in the plug by stroking the end of the wire against the earthed casing of the plug?
A. That is so.
Q. Supposing the end of the wire had been in contact with the plug, could that have been reproduced by vibration of the fan during running?
A. Yes, that is the most likely way in which it would occur underground.
Q. Always supposing that the fan was running at the time?
A. Yes.
Glaister, it will be recalled, stated in evidence that when this fan was restarted after moving up on the Sunday the press button was in order and worked satisfactorily, so it would appear that the broken connection inside the gate-end box was caused after that, most probably in getting the apparatus out of the pit and transporting it to Buxton.
On this evidence, therefore, it must be concluded that the possibility of the piece of wire between the plug and the socket used as an external earth having resulted in incendive sparking was very remote, though in certain circumstances the possibility could not altogether be dismissed.
It should be pointed out that the pilot circuit in this case was covered by a Buxton certificate of intrinsic safety, which in the light of the tests following the explosion may need to be revised.
There was a concensus of opinion among the technical witnesses that the fan could not have been running when the explosion took place and therefore could have no connection with it. This was based chiefly on the fact that two of the four belts used for driving the fan were found broken and lying in the fan casing. These had the appearance of having been cut or torn straight across by the fairing over the fan pulley which was dented in by the explosion, whereas, it was contended, if the fan had been running at the time the belts would have been cut longitudinally and would have been drawn into the blades of the fan. This was said to have happened previously when belts had broken.
Whilst in view of the clear evidence of the fan having been struck by a major force reaching it from some point outbye I was satisfied the explosion did not originate at it, it was important to know whether the fan was running or not, and, to clear up this point as far as possible, I considered it necessary to have a detailed examination of the fan and the belts carried out by a mechanical engineer; this was done by Mr. A. E. Crook, H.M. Mechanical Engineering Inspector of Mines after the Inquiry was closed, and his report is given as Appendix III.
This shows conclusively that the fan was rotating at a considerable speed when the inlet fairing, severely damaged by the force of the explosion, was brought into contact with two of the driving belts causing them to break. Having regard to the magnitude of the force necessary to so damage the fairing – and also to bring about the other damage seen in the immediate vicinity of the fan – and the speed with which such a force must have travelled, it seems to me inconceivable that the one force – there was no evidence of any other – striking the fan should have (in sequence) started it from rest, accelerated rotation to a high speed and then driven in the fairing with great violence to fracture the belts.
I am convinced that when the explosion occurred No. 3 fan was running in the normal manner.
(c) There were three points at which cables were found to have sustained damage, and in each case the cable was opened up and carefully examined; the conclusion reached in all was that the damage resulted from the explosion and had not been the cause of it; moreover, none of these damaged parts was within the immediate area in which the explosion was deemed to have originated.
Owing to their being buried under falls it was not possible to examine minutely all the cables, but they were all tested for insulation and conductivity without any defects being revealed.
My conclusion therefore is that the explosion was not caused by electricity.
Shot-firing –
On the morning of the explosion the only person in the No. 2 district responsible for the charging and firing of shots was the deputy, Tom Miller. He was issued by the colliery policeman and explosives keeper (Alfred Stephenson) with detonators in a locked tin – the key being kept by the deputy – but no record was kept of the actual number, the practice being to record the number at the end of the shift when the tin was returned and the number used was also ascertained. Stephenson said, however, that it was usual to issue 30 in the tins, which were filled up again at the end of the shift before re-issue, and that would be the number given to Miller.
As will be seen on Plan No. 1, after the explosion 22 detonators were found in No. 3 heading between Nos. 4 left and 5 right thirls – they were in two bundles of 10 each and two single. A tin was also found badly damaged with the lid severed, which it would seem had contained the detonators. If in fact Miller took 30 detonators into the district eight remain to be accounted for. It is possible some of them were set off by the explosion, or, as the manager suggested, they might be buried among dirt and debris which had not been cleared up.
The explosives were carried in by the men who were to use them and on the morning of 9th December, for the No. 2 district, one tin was issued to Hill and one to Chapman, each containing 5 lb. of Dynobel. Some four or five days after the explosion these tins were returned to the store. One remained full as issued, and a little (about a pound) had been used from the other.
In No. 4 heading some distance back from No. 5 right thirl a battery exploder was found with one lead attached; it was the practice in the headings to use two leads, one on each side of the road, and the manager explained that they were usually left lying in that position. A powder tin was also found in this heading, but Stephenson could not state definitely whether it was this tin from which the explosive had been used.
There was some argument as to whether a shot had been fired at the face of the extension to No. 5 thirl out of this heading. Robert O’Neill, a shotfirer, stated that on the Saturday morning before the explosion he fired six shots in this place – one by Cardox and five by explosives – most of the coal from which was filled out on that shift before he left, but probably four or five tubs would remain. The shots were not good shots and some sockets were left on. After the explosion he had seen this place, and had formed the opinion there was "a bit" more coal lying than on the Saturday, from which together with the fact, as he said, that after firing on the Saturday he left the exploder near the corner of No. 5 thirl and the No. 3 heading, he concluded that one or more shots had been fired on the morning of the explosion. He brought his detonators out with him to the surface on the Saturday.
On the other hand evidence was called to show that on the morning of the explosion the conveyor in No. 3 heading did not run as long as McMullen had estimated, that very little coal came out of it, and that the presence of the sockets from shots and the general appearance of the face indicated that no further shot had been fired.
There was general agreement that if any shot was fired in this place on the morning of the explosion it would be by the deputy Miller, but there was no suggestion by anyone that even if this did happen it had anything to do with the explosion. The positions in which the deputy, and the three men Nos. 2, 5 and 6 were found clearly supports this view, and I therefore conclude that shotfiring was not responsible for the explosion.
Electric Cap Lamps –
The electric lamps in use were all Oldham-Wheat Type "Q" cap lamps; some of the lamps were recovered complete and parts of others were found, and all were subsequently examined by Major Platt at the Mining Equipment Testing Station, Sheffield, who gave evidence on their condition as follows
I came to this conclusion, that a number of the lamps were in such a condition that they were not likely to have been the cause of any ignition in the mine. As regards other lamps which were incomplete – that is to say, the headpieces were missing, and those headpieces had apparently been wrenched away from the battery cable by force – whilst the batteries were in good condition, as also were the cables, I could not give any opinion as to the safety of the missing headpieces, and the doubt comes in as to the safety of those because I was unable to say whether those headpieces were in safe and good condition immediately before the explosion. If one of them had been smashed with respect to the protecting glass and the glass envelope of the lamp bulb, it is possible that gas might have been ignited by exposed incandescent filament. As regards the three smashed headpieces unaccompanied by any other part of the lamp, all three of those were badly smashed – I think it is quite fair to say, obviously by violence. Two of those headpieces had complete protecting glasses, but the glass envelope of the lamp bulbs was smashed, and it might be that the smashing of the envelopes of the lamp bulbs would have exposed the incandescent filament to gas, which would have entered the headpiece through the smashed moulding of the shell. I cannot say any further than that. As regards the third smashed headpiece – these are the three headpieces I received from Mr. Nussey subsequently – although the bakelite moulding of the shell was badly smashed, the protecting glass and the lamp bulb were both intact, and I suggest that that headpiece had no part to play in the ignition. I think that summarises what I found, sir.
By Mr. Sandlands –
Do not think I am raising this as a probable starter, but I want to eliminate it: It is a fact, is it not, that if the cable connecting the cap lamp to the battery carried by the miner is severed or broken, you might get a spark; which could ignite gas if the man was in it?
A. It can be done under certain circumstances, yes.
Q. It is just a possibility?
A. Yes.
Q. And it is also a fact that a cable which was perfectly sound on examination on the miner entering the Pit might get damaged in the course of his work?
A. That is so.
Q. It is only just to show that it has not been overlooked. You do not think in this case it is really a serious thing that we need consider?
A. No, certainly not.
Having regard to the area in which it was agreed the ignition occurred, only lamps numbered 139, 131, 156, 499, and 20 belonging respectively to Addison, Hill, Largue, Hoodless and Brown, need be considered.
The first three were in a complete state of assembly and were reported safe for use. Of No. 499 Major Platt reported that the cable sheathing was stripped back or 5 inches from the gland on the headpiece, but this stripping of the sheathing played no part as a source of ignition; otherwise the lamp was in safe condition.
The battery and cable of No. 20 lamp were in good condition, but the headpiece had been wrenched off. A headpiece which was thought to be that missing from this lamp was badly smashed, but the protecting glass and lamp bulb were still intact, and it was considered that this headpiece was not responsible for causing an ignition.
Although it is not possible to state with certainty that the lamp worn by R. Brown was undamaged before the explosion it would require some force to wrench the headpiece from the cable, and there was no indication of anything having happened apart from the explosion to account for this.
It seems to me most improbable, therefore, that the ignition originated from an electric cap lamp.
Flame Safety Lamps –
There were three flame safety lamps in the district at the time of the explosion. One of these, No. 51 an ordinary type miner’s lamp, was found intact, locked and in good order, near to the bodies of the brothers Bird in the old shuttle car workings, and on examination by Major C. B. Platt, Superintendent Testing Officer of the Sheffield Mining Equipment Testing Station, was found to be in safe working condition.
The other two were found in No. 4 left thirl in a damaged condition and dispatched as found to Major Platt who gave evidence as to his examination of them as follows :–
Two of the flame safety lamps were officials’ type lamps fitted with selfcontained internal re-lighters, and both of those lamps were received in pieces ; that is to say, they were not fully assembled. Lamp No. 2 was received with the bonnet and the gauzes detached from the lamp frame. The spirit vessel was in position and locked to the lamp frame. The fabric of the top of the outer gauze was dented and torn away, making that gauze unsafe, although the lamp would still be protected by an intact second gauze. With regard to the re-lighter of that lamp, the pyrophor bar, popularly called a flint, and the compression spring which presses the flint on to the friction wheel of the re-lighter mechanism, were both missing, although the small brass cap which holds those two components in the re-lighter mechanism was present and properly assembled in the re-lighter. All the other parts of the lamp were intact.
As regards lamp No. 17, all the parts of this lamp were received in good order and properly assembled, except that the spirit vessel was unlocked and received by me unscrewed and separated from the body of the lamp. The top surface of the spirit vessel, which is normally protected against dirt by the base of the lamp frame, was heavily coated with mine dust.
Lamps Nos. 2 and 17 were produced and inspected in court. As regards the latter Major Platt showed that the screw-thread was perfectly efficient, and said if the spirit vessel had been wrenched off by the explosion he would have expected the threads to be badly damaged and stripped, but they indicated no undue play or wear.
Questions were put to Major Platt as follows :–
By Commissioner –
Q. Major Platt, the effect of what you have told us is this: that so far as No. 2 lamp is concerned you are satisfied that the damage which you have described could have been caused by the explosion ?
A. As regards the removal of that bonnet, I think so; possibly the damage to the outer gauze.
Q. Possibly the damage to the outer gauze
A. Yes.
Q. And even so, there was still one gauze left undamaged?
A. That is so.
Q. And as regards No. 17, you say, I gather, quite definitely that it would not be possible to unscrew the oil vessel and expose a naked light to the outside atmosphere?
A. That is so, yes.
By Coroner –
Q. What could have been the purpose of unscrewing this No. 17? Whoever did it, what could have been the purpose of it?
A. That lamp is fitted with an internal relighter which might not have been working efficiently. Cases have been known of lamps being opened with a view to adjusting the working of the internal relighter. It is a very unsafe thing to do, of course.
By Commissioner –
Q. If it were opened in the pit (we have not any evidence of that yet, of course, nor may we have), that might have been a possible reason for opening it?
A. It might have been.
Q. To adjust the relighter?
A. Yes, but that is a highly dangerous operation.
Q. Why?
A. Because when the spirit vessel is removed from the lamp the inside of the lamp is left wide open to the outer atmosphere, and the Pyrophor relighter can produce a spark which would light gas within the lamp and the flame would come out through the top, which is normally filled by the burner of the lamp.
Q. So that with the vessel unscrewed the relighter could be worked and produce a spark?
A. Exactly. For the Coroner’s benefit, I may explain that the Pyrophor relighter is, in effect, exactly the same in principle as a cigarette lighter.
As regards No. 2 lamp (which belonged to the overman Hoodless) it seems to me reasonable to conclude that the damage occurred either some time before or resulted from the explosion, and that since its inner gauze was still in good condition it could not have been responsible for igniting firedamp in what must have been a more or less quiescent atmosphere. No. 17 lamp, however, presents a very different position which demands serious examination.
The oil vessel or well of this lamp was found detached from the rest of the lamp, the vessel being about mid-way along No. 4 thirl and the remainder at the junction of No. 3 heading with that thirl and near the body of Hoodless.
In a signed statement the Manager (Mr. Graham) asserts that at about 3 p.m. on the day following the explosion he was on one side of the brattice sheet erected across No. 4 left thirl about 10 feet from the side of No. 3 heading and Mr. Hughes (the Agent) was on the other side. "When I rejoined him he gave me the well part of a flamelamp and showed me where he had found it. I gave it to Joe Pattinson, Chief Electrical Engineer, who put it in his pocket and took it to the surface, where it was kept in the surveyor’s office until it was dispatched to Sheffield. I marked on the master plan under the supervision of the surveyor the place in which Mr. Hughes told me he had found the part of the lamp. This part was the one subsequently identified as belonging to No. 17 lamp. Both parts of the lamp are in my possession and they are, in my opinion, in a similar state to that in which they were found, except that they have been cleaned."
Thomas Nicholson, an overman, who was captain of one of the Rescue teams, descended at about 9 p.m. on the night of the explosion to explore the No. 3 heading, the air of which they found very thick. In one of the left hand thirls he asserts about 5 or 6 feet round the corner he kicked a flame lamp top which he picked up, brought back into the heading and placed on the belt conveyor. Here it was subsequently seen by the undermanager and others and its position marked on the plan. Nicholson did not see the well part of the lamp.
From this I am satisfied beyond any doubt that the two parts of this lamp were found detached in the positions stated, and since the screw threads of the vessel were in perfect condition and the lamp could easily be re-assembled by screwing up the vessel (as was done in Court) the vessel must have been unscrewed and removed from the body of the lamp before the explosion.
The lamp belonged to the deputy Miller, who when the explosion occurred was some 300 yards away from it. Why he had gone outbye and why in doing so he had left his flame lamp behind it is not possible to say, though if his journey was to be restricted to the main conveyor road he would not, of course, be likely to need his flame lamp as he had an electric cap lamp. Moreover, the flame lamp would be more likely to be useful to the overman who was engaged in clearing gas from the headings inbye, particularly if Hoodless’ lamp was out of order.
The manager and other witnesses spoke in the highest terms of the experience and personal qualities of the overman, deputy and the deceased workmen, and considered that none of them would be guilty of illegally opening a safety lamp in such circumstances. While appreciating this attitude of confidence in the integrity of these officials and workmen, the fact has to be faced that the lamp was opened by someone, and I think an explanation can be offered which, without condoning the offence, affords reasonable grounds for the action taken.
I do not for a moment suggest that Hoodless would knowingly open the lamp in the presence of firedamp ; but what was the position which confronted him?
Three men (Nos. 8, 9 and 10 on plan) were working near No. 3 fan ; they were either in or on the fringe of an accumulation of firedamp and they had no means of ascertaining the condition of the air. It was suggested in evidence that these men were either engaged in erecting or had just erected a brattice sheet across No. 3 heading at the fan, and there could, of course, be no object in putting up such a brattice unless the fan was running or was about to be run. It was essential that Hoodless should know what was happening to the gas in that region, especially if, as I am satisfied was the case, the fan had been started.
If, as I think it reasonable to assume, No. 2 lamp was out of action – it might possibly have already been damaged or, if it had been extinguished it could not be relighted because of the missing pyrophor bar – he was left with No. 17 lamp borrowed from the deputy. He had possibly been up to these men to make a test with this lamp and had had the light extinguished and it failed to relight. To relight or examine it, or to get another lamp he would need to go a considerable distance outbye and waste valuable time. In his anxiety to get the ventilation restored and the headings restarted, why should he not take the lamp outbye to a spot he considered to be free from firedamp, and there examine it and carry out any necessary adjustment? No. 4 left thirl would seem to him to be a proper place for this purpose, since it was close to No. 2 fan which was blowing fresh air up the No. 3 heading, and No. 5 right thirl was partially open allowing some fresh air to pass up the heading through the thirl and down the No. 4 return.
Such were the circumstances in which I visualise the lamp being opened. After removing the oil vessel Hoodless was, I think, trying the relighter when it operated and ignited firedamp. The medical evidence showed that he was burned but suffered no external injury from violence, the cause of death being lack of oxygen and carbon-monoxide poisoning.
All the evidence points to there having been at this point an inflammable mixture which continued inbye up No. 3 heading, the percentage of firedamp in the air gradually increasing until somewhere in the region of No. 5 left thirl it reached explosive point and there exploded with great violence. The No. 3 fan was projected several yards inbye, the three men near suffered very serious multiple injuries, and the chain conveyor engine was thrown inbye and the pans doubled round the corner of the No. 6 left thirl. The explosive force passed through the No. 6 thirl into No. 2 heading and thence right and left. In its passage down No. 3 heading the flame entered No. 5 right thirl at the extension of which, or at the face of No. 4 heading, there was some augmentation of firedamp which caused victims 2, 5 and 6 to be severely burned without otherwise suffering serious physical injury.
How is the presence of firedamp in inflammable mixture so far down the No. 3 heading to be accounted for, having regard to the evidence of deputy Hannah as to the position when he left the district? The explanation, in my view, lies in the starting of No. 3 fan, and this I am convinced was the factor which the overman failed to take into account and by which he was deceived. The capacity of this fan with the louvres full open (as Fisher stated they were when the fan was run in its new position after moving up on the Sunday) was 8,750 cubic feet per minute, but assuming the louvres were set at a slight angle and therefore not quite fully open the quantity capable of being circulated by the fan can be taken as about 8,000 cubic feet per minute. What was the quantity reaching this fan?
According to the evidence of McGregor, the total quantity of air entering the district, as measured in No. 3 heading at the air crossing averaged less than 17,500 cubic feet per minute. This air passed up No. 3 heading to No. 2 left thirl when it split, part of it going through that thirl into No. 2 heading where No. 1 fan was situated and the remainder continuing up No. 3 heading.
The No. 1 fan was of the same type and size as No. 3, but was said to be operated normally with the louvres set from half to three-quarters open; thus it would be taking not less than 5,000 cubic feet per minute. This split returned down No. 1 heading where there was a regulator set (according to McGregor) to an orifice of approximately 20 square feet. It is apparent from the ventilation plan (No. 2) that some air would pass direct into the return additional to that taken by the fan, and this I assume to be about 500 cubic feet per minute making in all 5,500 cubic feet per minute circulating in that split. The quantity going forward up No. 3 heading to No. 2 fan would therefore be no more than 12,000 cubic feet per minute.
No. 2 fan was capable of dealing with 5,000 cubic feet per minute. It will be recalled that when Hannah diverted the tubes for this fan from No. 5 right thirl to blow direct up No. 3 heading he opened the brattice sheet in that thirl (the opening being approximately 24 square feet), and the undermanager, deputy Hannah and other witnesses were agreed that with this opening – the regulator at the outbye end of No. 4 heading remained unchanged – the same quantity might be expected to return by No. 4 heading as would be circulated by the fan with the tubes in their normal position, i.e., 5,000 cubic feet per minute.
Thus the total quantity passing up No. 3 heading beyond No. 5 right thirl cannot have exceeded 7,000 cubic feet per minute even without allowing for leakages between the intake and return outbye of which there must have been some. The brattice sheet in No. 5 left thirl had been opened by Hannah in his early efforts to clear the accumulation of gas and later closed again after he had opened No. 6 left thirl, but it was probably not left very tight. In any event some leakage would occur here.
All this to my mind clearly establishes that the quantity of air reaching the No. 3 fan was insufficient for its requirements. What the actual deficiency was can only be surmised, but it is of interest to note the estimate which the undermanager gave in reply to Mr. W. E. Jones as the quantity reaching the fan as follows :–
Q. What amount of air would you consider would be passing along that road at that particular time? Have you any estimate of the quantity of the air that would be available for ventilating that roadway?
A. 6,000 or 7,000 cubic feet as near as I can say at that time.
Q. 6,000 or 7,000 cubic feet per minute at the time the cloth had been removed in 5’s thirl
A. No. 6 thirl.
Q. No, wait a bit. First of all, you have made provision for circuiting the air into 4’s return ?
A. Yes.
Q. To what extent would that reduce the quantity of air available for ventilating the straight?
A. It would not reduce it any.
Q. How do you come to that conclusion?
A. Because we had already got a blower fan at this point taking air from this main ventilation which was already going into No. 4 and there was no more ventilation going through that point than what there would be when the fan was blowing.
Q. Would the normal ventilation passing along 5’s thirl into 4’s return not be in excess of that blown into that particular area by the blower fan ?
A. There would not be much variation in it; very little.
Q. And you come to the conclusion that normally, under ordinary circumstances when the blower fan was working you would have 6,000 or 7,000 cubic feet of air passing inbye up the straight
A. Yes.
I consider even the lower estimate of 6,000 cubic feet per minute most probably erred on the excessive side, but in any case the running of the fan was bound to result in re-circulation of the air.
Mr. Graham placed the start of the "blast" in No. 3 heading just in beyond No. 5 left thirl and Mr. Hughes suspected the point of ignition to be between No. 4 left thirl and No. 5 left thirl, the force developing inbye (which agrees with my own view), but both went on to account for gas in this area by assuming that by some means (probably the falling down of the sheet unnoticed) No. 6 left thirl became blocked, and the No. 2 fan, the tubes from which they suggested had been extended up to or beyond that point, forced the gas back down No. 3 heading and fouled that road.
If the sheet in No. 6 left thirl was closed (as seems to me likely) the more reasonable explanation is that it was closed deliberately by Hoodless or his men when No. 3 fan was started. The effect of running that fan would then be to draw air charged with firedamp from the return (No. 2 heading) through No. 5 left thirl, and possibly to a lesser extent through No. 4 left thirl, into No. 3 heading (and also to force gas back from the face down that heading) so creating just the conditions to produce the results which were afterwards found.
That, I am satisfied, is what took place.
Incidentally Mr. Graham spoke to evidence of the explosion having passed from No. 3 heading not only through No. 6 left thirl but also "through No. 5 left thirl and thence down No. 2 heading to No. 4 left thirl where it was joined by violence, not excessive, which had come down No. 3 heading to that point and passed through No. 4 left thirl." The course of the explosion as thus described confirms my view that air containing gas was being circulated between No. 4 left thirl and the No. 3 fan.
Whether coal dust played any part at a later stage in the explosion it is very difficult to say. The workings at, and for some distance back from the face were definitely wet with water raining from the roof in places, but tended to become drier, though still by no means dry, farther outbye. Mr. McGregor stated that he regularly tested the roadways to see whether there was any dust which could be dispersed by blowing upon but could find none, and therefore no samples were collected for analysis, and for this reason it appeared that no stone dust was applied.
Samples were collected by Mr. Nussey on 11th December, though admittedly it was not easy to obtain them, and two of these taken in No. 3 heading – one between the 2nd and 3rd left thirls, and the other between the air crossing and the first right thirl – on analysis gave only 37.5 and 40.3 per cent, respectively of incombustible matter.
From the No. 3 left thirl the explosion proceeded outbye chiefly by way of No. 2 heading, but to a lesser degree also down Nos. 1 and 3 headings until it reached No. 1 level at which point there was very considerable violence ; the brickwork and door in No. 2 heading were blown out into No. 2 level, the air crossing at junction of No. 1 level and No. 3 heading was demolished, and the conveyor in No. 3 heading outbye of the air crossing was thrown about and badly damaged, the deputy’s body being found in a mangled condition among the wreckage. There were also signs of fairly intensive heating at the outbye end of No. 3 heading and in Nos. 1 and 2 headings.
It would appear, therefore, that more gas was picked up at about No. 3 left thirl (probably from the old shuttle car workings), and to this I attribute most of the damage outbye, but I cannot with certainty rule out the possibility that along the lower part of No. 3 heading the explosion was extended by coal dust.
One witness said he heard what appeared to be two ‘bangs,’ the first much more pronounced than the second; if this be so, the first was probably the main explosion at the inbye end of No. 3 heading, and the second the demolition of the air crossing.
Cause of the Accumulation of Firedamp –
The Management claimed that the ventilation arrangements were adequate and the evidence showed that up to the Sunday prior to the explosion no trouble had been experienced. They contended that the accumulation in this instance was due to the fall at the junction of No. 2 heading and No. 7 left thirl having occurred some time on the Sunday previous to Hannah’s inspection, and that the closing of this connection, preventing the through circulation of air between the two advance headings, accounted for the accumulation. Evidence was given that additional water was raining from the roof at this spot making the strata slippery and tender, and that during the previous week extra supports had been set to strengthen the roof. Richard Norman, an overman, deposed that after the explosion, about the middle of January, he was instructed to make a special examination of the place to find out when the fall occurred. On the left side on the coal above the original roof he found a spattering of what he termed ‘slush,’ and alongside this fall standing up towards the coal was a prop the top of which also was spattered with mud. On this prop he also saw evidence of coking. From these he concluded that the spattering was caused by the explosion, and that the fall therefore occurred before the explosion.
Mr. Price, who gave expert evidence for the owners, also said he had seen the spattering of mud – this was six or seven weeks after the explosion – and had reached the same conclusion.
On the other hand the undermanager saw this place on the Friday before the explosion; it was then in order and he had no reason to anticipate further trouble there. Deputy Fisher also said that when he left the district on the Sunday morning there was no fall at this junction, and no movement suggesting that a fall was likely.
The first person to reach this junction after the explosion was Thomas Hodson, the captain of a rescue team from Risehow Colliery which descended the mine at 4 o’clock on the Tuesday morning. He described the fall as pyramid shaped, the centre of which was right in the centre of the junction and tapering away in all directions. There was a space 18 inches high over the fall, but as he and his men were wearing apparatus they increased this by another foot by clearing away some of the stones, and they were then able to go up to the face of No. 2 heading and the thirl. also through into the return outbye of the thirl.
By Commissioner –
Q. Would you conclude that there was a reasonable space for ventilation to go over that fall and down back No. 2 heading?
A. At 18 inches high, sir, and your roadways were 6 to 7 feet high, it would make the air sluggish.
Q. I agree, if you have a fall like that you have impeded your ventilation; there is no question about that. Do you still think there would be space to allow a reasonable quantity of air to pass?
A. There should be no gases collected on top of the fall, 18 inches should allow quite sufficient air to get through.
Mr. McCracken, the undermanager, saw this fall on the night shift of the Tuesday – several others had passed over it in the meantime – and although the height over it varied he agreed that at the time of its occurrence it would average about 18 inches, and that would not cause a complete blockage of the ventilation.
Even if the fall was a pre-explosion one, therefore, I am satisfied that it did not block the passage of air through No. 7 thirl, though it would reduce it.
It was further suggested by the Agent, and Mr. Price supported this, that the fall at this junction, consisting of about 3 feet of coal and 4 feet of stone, liberated firedamp which contributed to the accumulation. If this did occur it seems to indicate that the ventilation lacked any driving power to deal with it since at least part of the gas would be emitted into the return opposite to and on the outbye side of No. 7 thirl, which in any event would not be closed immediately and according to the evidence was not completely closed after the explosion.
In my view the accumulation was due chiefly, if not entirely, to a natural emission from the seam in Nos. 2 and 3 headings which the ventilation was inadequate to meet when the auxiliary fans were standing.
As stated on page 6 deputies had reported some accumulation on previous occasions when an auxiliary fan was stopped; the undermanager also said he had found gas occasionally "when the ventilation was disrupted" though not recently, and other witnesses agreed that when the fans were stopped gas might be expected to accumulate. That it was not reported more often following a stoppage was due no doubt to the practice of the deputy in each case starting the fan when he reached it, and leaving it running some time before he made his inspection.
These headings were being advanced at the rate of nearly 10 yards per week and were of large sectional area with coal roof and floor as well as sides, all of which might be expected to increase the emission of firedamp. Their large area, commendable on other grounds, had also the effect of reducing the air velocity, and as this was insufficient to turn the anemometer the quantity of air passing was not measured. Moreover, it is more difficult to prevent firedamp accumulating in rising headings than in dipping or level ones, and a greater impact of fresh air is necessary to move an accumulation. There was no sudden fall of barometric pressure to account for the accumulation.
I cannot escape the conclusion that the ventilation had not kept pace with the rapid face advance, and that the point had been reached where the quantity of air reaching the face, sufficient in the past, was inadequate to meet present needs.
While the No. 3 fan was kept running the air would be kept in motion and, on the evidence, appeared to be in order (though some re-circulation was probably taking place), but when the fan stopped the air became sluggish and unable to prevent an accumulation – the headings it will be noted were some 40 yards in advance of the last thirling. In such circumstances the fan should have been kept running continuously and not stopped for lengthy periods at weekends. Moreover, steps should have been taken to increase the quantity of air in the general current in No. 3 heading reaching the fan, the capacity of which was unusually large. The likelihood of re-circulation would be increased by the moving up of the fan on the Sunday since there was only sheet in No, 5 left thirl,
If a fall did occur at No. 7 junction on the Sunday afternoon this would aggravate the position, but I feel sure the primary cause of the trouble was as stated above.
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