Consideration of Possible Causes

Contraband was not found in the workings or in the clothing of any of the victims, and accordingly smoking or the illegal use of a naked light has been ruled out as a possible source of ignition.

Detonators or explosives were not issued to any of the missing men during their shift and indeed none had been issued for a week previously; nor were any found in the district. All the seven safety lamps, electric and flame, in use in the district were examined at the Safety in Mines Research Establishment of this Ministry and passed as safe, except broken lamps whose damage, I am satisfied, was consequential to the explosion. Safety lamps are therefore dismissed as an igniting cause. There was no indication that frictional heating of any description had played any part in the explosion. and compressed air was not in use in the district. There is no history of spontaneous heating at the mine, nor evidence that such heating existed at the time of the explosion.

The only electrical apparatus in the district which is known definitely to have been running during the shift, and which there can be little doubt was actually running when the explosion occurred, was the turbine pump. In the events which followed afterwards, this pump and its associated switchgear were submerged under water for fifteen months and also buried under falls which took place some time, but not immediately, after the explosion. In the subsequent recovery operations these were the last pieces of apparatus to be recovered and examined. It will be readily understood that, after such a lapse of time during which they were subjected to the corrosive action of the pit water and to the pressure from the fallen rock, they suffered considerable damage. Nevertheless, it was found possible to examine them and subject them to tests. The motor was brought to the surface, dried out and tested under power and found to be in working order. The switchgear, which had been newly installed three weeks prior to the explosion, was found to have sustained severe internal and external corrosion; nevertheless when those parts which had been adversely affected by the immersion were replaced, the switch was found to function in a proper manner. In view of these findings I conclude that neither the pump motor nor its switchgear played any part in the initiation of the explosion.

Although a definite cause of the explosion was not ascertained, it is a fact that the only possible igniting medium found in the whole course of the protracted investigation was the fusion on the shuttle car battery. Furthermore, I am satisfied that the explosion could only have occurred as a result of something done by the men in connection with the operations in which they were engaged near where their bodies were found.

For reasons which I shall consider later, it is reasonably certain that the ventilation had been restored, or partially restored, to the 3rd North Flat and that an attempt was being made to boost it on to the 3rd East Flat. These activities were directly connected with the explosion, which certainly would not have taken place if :–

Without the use of electrical power and the shuttle car in the 3rd North Flat, it is almost inconceivable that any dangerous situation could have arisen during the restoration of the ventilation.

An examination of the events as they occurred from Tuesday, 25th September, 1951, must be made in order to arrive at an explanation for what appears to have been unexpected action on the part of Thomas Whitney, who was a deputy of many years' experience, trustworthy and reliable.

On the day the manager short-circuited the ventilation, he and his officials knew that it would result in gas accumulating in the workings and cause them to be fenced off ultimately. It was also the end of the producing life of the district, although it was not intended to abandon the district until some future date when the valuable machinery in it had been removed. As the ventilation in the district had been interrupted by reason of the fall, the action taken in short-circuiting the ventilation was fully covered by Proviso (b) of Section 29 (1) of the Coal Mines Act, 1911. Indeed, there was no other choice if a foothold in the district was to be retained, because the running of the pump was a prime necessity. Later that day and during the next. the manager consulted with the undermanager and decided that he would fix the date of the restoration of the ventilation only after the cause of the interruption had been removed, and he commented on plans he had in mind for salvaging the machinery. The substance of these talks was made known to the overmen, not for the purposes of action but only to keep them informed. Neither the manager nor undermanager went into the district again. nor did they speak to or see Whitney although they kept themselves fully informed as to the situation by means of the deputies' reports, in which were entered particulars giving the build-up of gas in the district and the position of the fences as they were erected.

Whitney, however, was aware of the salvage plans because on Thursday, 27th September, he informed Vincent Love that he (Love) was to be a member of a team of salvage men whose first job would be to withdraw all the machinery to a point as near as possible to the conveyor road, where it would be held until this roadway had been so enlarged that it could be sent out. Whitney was not at work after the Friday until the shift on which the explosion occurred, when he would find the conditions had materially improved over the week-end, due to the passage which had been made over the fall. Although in what he next did he might have acted contrary to the management's intentions, I dismiss the suggestion that he acted contrary to instructions, for I am satisfied he was not given any of a precise nature. Hence. when he went into the district he had to formulate his own plans in accordance with the conditions as he found them and with the salvage proposals of which he had become aware. The ventilation no longer being interrupted, and in the absence of orders to the contrary, Whitney might well have considered it his duty to take steps to restore it, a pre-requisite of which was the closure or partial closure of the door and screen on the conveyor road. If he closed the door fully, he would have had the whole of the ventilation in the district, amounting to some 5,000 c.f.m. available, but it is inconceivable that a man of his experience would do so. for he would undoubtedly realise that this would result in the pump having to be stopped because the main body of inflammable gas would be moved down through the pumphouse. He could, however, so adjust the door that a portion of the air would be directed up 3rd North and the remainder continue to flow into and through the pumphouse. and I consider it not unreasonable to assume that the quantity he took off into 3rd North would not exceed half of what was available, that is not more than 2,500 c.f.m.

There is little doubt that he succeeded in moving the gas up to 3rd North and along the 7th (K.31-34) Level, past the bank of gate-end switches, for he must have had some ventilation in to that point in order to reach the fan which was then situated near K.34. Furthermore the weight of the fan, without its cable, was over four hundredweights. so that some mechanical assistance would be necessary to move it, and this was to hand in shuttle car No. 924, parked at the top of 3rd North. Whitney. from all accounts. was not a man to take liberties with shuttle cars; it was known for instance that he was particularly insistent that the covers be kept over the batteries, and I do not believe he would have used the car, as I have no doubt he did, unless he was satisfied that there was no danger from inflammable gas.

What then was his motive in moving the fan and setting it to operate at the 6th Level junction? I think the answer lies in this, that clearing the gas up 3rd North was comparatively easy, for it was a case of rise ventilation. Having pushed it up 3rd North and eastwards along the 6th and 7th Levels, it now had to be moved downhill. through a single road, into the 3rd East Flat. not only against the resistance of the roadways but with the added drawback that the door on the main intake was only partly closed, and hence the difference in resistance to the passage of the air as between the partly closed door and the circuitous route around 3rd North and 3rd East was becoming less and less, so it is conceivable that the greater part of the air would be passing through the door and very little going up 3rd North. It would seem that he put the fan at J.31 junction and arranged it to blow eastwards along J. Provided sufficient air was passing the fan, this action should not have given rise to any re-circulation, but if, as seems probable, the quantity reaching the fan was less than its capacity, 3.000 c.f.m.. then re-circulation was bound to occur. There was some evidence of there having been a sheet or stopping in J close to the fan, so that, of the air blown in along J, some would tend to pass up 33 stenton to K Level and travel back along K to 3rd North and so back to the fan. This air would entrain some of the inflammable gas still pent up in these innermost workings and in quite a short space of time an inflammable, if not an explosive, mixture of gas could be trailed out along K Level.

If, coincident with this bringing of an ignitable mixture along K Level, the battery covers had been removed so exposing the cells and cell connections, an incendive spark could have been produced if these latter had been short-circuited by any conducting material, as, for example, a metal tool or by a blow such as might result from a fall of roof.

To account for the removal of the covers one has to take notice of the practice which was in vogue, of shorting out defective cells or re-connecting cells whose lead connecting links had fractured, with copper strip clamped to the lead links. The bolts securing the clamps, it is known, tended to loosen in time, and a loose connection would seriously reduce the power output of the battery and might even bring the car to a stop. It would seem that the shuttle car had been taken from its parking place, which was on a rising gradient just inbye of K.3 1 junction. run forward downhill slightly, then back and to the right along K Level to the fan, then forward again to 31 and down it to J and back up towards the parking place. But it had not actually arrived back to its original position and, as found, was half blocking the entrance to K Level and standing on a slightly steeper than normal rising gradient. If, having all but completed this journey, all except the last part of which had been on the level or downhill, it failed just as it was about to be put back, what would be the natural reaction of whoever was running it? It should be borne in mind in this connection that all the men at work in the district on this shift were skilled in the operation of shuttle cars. Accordingly, it is not improbable that the covers would be removed to examine the bolts on the temporary connections, of which there were several. It would be ordinary prudence to withdraw the battery leads, I suggest, and if then in attempting to tighten a nut two of the cells were accidentally short circuited, there would be the spark, ready to ignite a trail of gas which would burn back towards the main concentration and be followed by the explosion.

I consider this to be a possible explanation which is confirmed to a certain extent by evidence. For instance, two of the four bodies were found at J junction and the other two half a pillar outbye. all with their heads pointing outbye suggesting that they were running out when the explosion occurred. The two farthest outbye were the two youngest men who would be the most likely to run out quickly and their positions were not inconsistent with the distances they could have covered between the time of ignition of the gas and the overtaking of them by the explosion.

The use of the fan and the choice of site can only be explained on the assumption that it was being used to speed up the rate of clearing the gas. In so doing, however, Whitney was using it as a booster fan and was therefore acting contrary to the requirements of No. 15 of the Coal Mines (Ventilation) General Regulations. 1947. It is evident that, in his consideration, he omitted to take into account the fact that the capacity of the fan might be in excess of the quantity of air reaching it and hence that it could give rise to re-circulation.

From the amount of work which had been accomplished there seems no doubt that Whitney and his men had spent the greater part of the shift in dealing with the ventilation. It is a pity therefore that, according to Overman Short who is the only living person who can say so. Whitney was not more informative when speaking on the telephone at 3.0 a.m., at which time the conversation was apparently limited to the question of the supply of a trailing cable. Whitney had no reason to be secretive about his actions which he would, in any event, have disclosed to his superiors at the end of the shift.

The Power Supply to 3rd North Flat

As, except for maintenance purposes, the turbine pump ran continuously from Tuesday, 26th September, until the explosion occurred, the whole of the electrical system as far as all the gate-end switches was also "alive". For some days before the explosion, the general body of the air along a considerable length of the 3rd North Road contained more than 1¼ per cent. of inflammable gas, and throughout the length there was a power cable from which the current had not been cut off as required by Section 60 (2) of the Coal Mines Act, 1911. All the officials of the mine familiar with the electrical lay-out were aware of the presence of the gas and they were remiss in failing to see that the cable concerned was disconnected, a matter which would have involved stopping the pump for about a quarter of an hour only. The provision of a separate isolating switch for that particular circuit would have been much better practice, however, as the power could then more easily have been cut off.

Shuttle Cars

The charging of shuttle cars outside the precincts of the charging station was contrary to the requirements of No. 15 of the Special Regulations in force at the mine relating to the use of shuttle cars underground. This was done with the knowledge of the electrical staff, and the practice must have been within the knowledge of the management for they were aware that shuttle cars could not be taken into the charging station and that the 3rd North Flat was still producing coal which could only be transported by shuttle car.

The presence of shuttle car No. 924 in the gaseous atmosphere in the 3rd North road was not in compliance with Section 60 (2) of the Coal Mines Act, 1911, in that its batteries and cable leads comprised electrical apparatus from which the electric current had not been cut off. The primary sources of power in such units are batteries, which cannot be switched off and cannot be housed in flameproof containers, and accordingly, as an ordinary safety precaution, machinery of such a type should not be left in any place in a mine where a dangerous percentage of inflammable gas is likely to occur. Indeed, in the event of a shuttle car being at a place when the inflammable gas content increases beyond 1¼ per cent., I am at a loss to suggest what action should be taken with regard to the car as either the action of driving it out or the inaction of leaving it. equally contravenes that Section. Nevertheless, when the ventilation was cut off from the 3rd North Flat. there was a serious omission on the part of the management and the officials in failing to ensure that all shuttle cars in the district were brought to a place where there was little likelihood of inflammable gas accumulating.

The examination of shuttle car No. 924 brought to light the practice, which was proved not only to be common but to be a recommendation of the manufacturers, of cutting out faulty cells or repairing the fractured connecting links of cells by severing the connecting links and "bridging" the adjacent cells by means of stranded copper wire secured by bolts. In this way, electrical continuity was temporarily re-established in the battery. Faulty cells and fractured links develop through the rough conditions in which shuttle cars are sometimes required to work and they may take place at any time, their effect being to bring the car to an immediate stop. The "bridging" operation can give rise to a serious hazard through the risk of open sparking taking place as soon as the battery tops are uncovered and the work is started. The risk will be greater if breakdown occurs at the working face.

General Regulation 132 states that "in any part of a mine in which inflammable gas. although not normally present, is likely to occur in quantity sufficient to be indicative of danger . . . pressure shall be switched off during the whole time that examination or adjustment disclosing parts liable to open sparking is being made." As a battery cannot be switched off, I fail to see how the spirit of that Regulation can be observed during a "bridging" operation in a working district. Nor can I see a practical alternative to "bridging". It is extremely difficult to tow a shuttle car as it is so highly geared between its driving motors and wheels.

Further investigation into the operation of these particular shuttle cars disclosed that their drivers had seen electrical sparking take place on the battery covers when a piece of steel – for example, a Cardox shell – was placed on them, and in fact they had sustained slight shocks. These stray currents would apparently be produced from slight leakages of acid from the cells, when the resultant capillary effect across the battery tops formed a conducting path between the battery and the shuttle car chassis. The colliery electrician estimated that the strength of these leakage currents could amount to as much as 2 or 3 amperes, which would be sufficient to ignite an inflammable firedamp / air mixture.

The extremely hazardous conditions which arose at the charging station by its partial collapse could not have been foreseen fully, but they emphasize very strongly that, as elsewhere in the mine, support at charging stations must be of a robust character, such as might be provided by the incorporation of a steel girder framework. The spillage of acid must be carefully avoided by proper handling as well as by the provision and use of the correct type of lifting and shifting equipment for the batteries. Any acid spillage should be removed forthwith.

The foregoing observations throw new light on the possible hazards which can arise in connection with the use of shuttle cars, and accordingly I do not feel it unreasonable to recommend that shuttle cars should not be used where there may be danger from inflammable gas.