Tweet

Electricity was in use at the West Stanley Colliery in the form of 40-period three-phase current at 550 volts. It was used chiefly for power, but there was a little electric lighting in addition.

Current was led from the generator to a switchboard in the generator house and distributed thence by separate switches to surface buildings and to pit.

Current was carried down the pit by means of three 37/14 copper cables insulated by dialite composition but unarmoured. The sketch attached shows diagrammatically the disposition of the various seams in the pit, and indicates the amount of electric power in each seam.

The three mains leading to the pit were controlled by a single triple pole oil-immersed switch and three fuses, the latter of 150 amperes capacity, all on the main switchboard in the generating station.

Beginning at the shaft-top the first motor was a 25-h.p. motor for driving a pump in the Brass Thill seam. This motor was not running at the time of the accident, and it had in fact been shut down for some time previous to the accident.

At the Towneley seam the shaft cables were brought into a disconnecting box and three fuses of 150 amperes capacity controlled the supply in this seam. Cables from this disconnecting box were carried by separate circuits to

Of these motors the evidence at the inquest showed that the 100-h.p. haulage motor alone was running at the time of the accident. The two coal cutters would not in the ordinary course have been started until 5 p.m. or after, whereas the explosion took place at 3.30 p.m. Further, the gate-end switches in each case were found to be open, and the trailing cables were not connected to the coal cutters. With regard to the small pump, the switch again was found to be open, and the body of the man who ordinarily attended to the running of this motor was found at the shaft bottom, where the additional duty he had of "rapping up" the men would take him at about the time of the explosion.

The haulage motor which was undoubtedly running at the time of the explosion will be referred to hereafter.

At the Tilley seam there was a cable leading in-bye to a coal cutter. The same remarks apply to this coal-cutting machine as to those in the Towneley seam – that is to say it is conclusively established that this coal cutter was not running at the time of the accident.

At the Busty seam the shaft cable ended and separate circuits were taken from a large disconnecting box to various circuits as below

The motors in the Brockwell seam will be dealt with hereafter. With regard to the 100-h.p. pump motor, from the evidence of the colliery engineer (Mr. Stephenson) this motor appears to have been running at the time of the accident. The two small pumps in-bye were, however, not running, as the switches controlling them were subsequently found to be open and locked off. It appears to have been customary to lock the switches controlling these small pumps in the "off" position when the pumps were not in use, and in this condition they were found. The "creeper" motor switch was also found in the "off" position.

The pump motor, as it was running, will be further considered.

With regard to the plant in the Brockwell seam, it actually consisted of the following

Of these motors the air compressor had not been running for some months previous to the accident. As to the coal cutter it would not in the ordinary course have been started up until 5 o’clock. Further, the gate-end switch was found to be open and the trailing cable was disconnected from the machine. It is therefore certain that this coal cutter also was not running at the time of the accident..

From the above it is clear that, apart from lighting, at which there was a little at Busty shaft bottom (20 lamps) and in the near Towneley haulage motor house (15 lamps), the only electric apparatus in service at 3.30 p.m. on February 16th was the haulage motor in Towneley seam and the main pump motor in Busty seam, the two largest motors in the pit. All the lamps were within a few yards of downcast shaft.

Certain tests have been made on these motors and on the cables leading to them. The controller and stator of the haulage motor are undamaged. The main switch and the resistance grids are,. however, badly damaged; from all appearance by the dynamical effect of the explosion. The cable leading to this motor was found under a heavy fall, but nevertheless though broken down between. two of its cores its insulation to earth was still over 5 megohms. When the fall had been cleared careful examination showed no indication of external Bparking from this cable.

With regard to the pump motor in Busty seam, both the motor itself and the cable leading to it from the disconnecting box at shaft bottom were shown by test to be undamaged. Further, the indications of explosive force in the motor house are practically non-existent, as evidenced by the general appearance of the plant and gear, and the fact that two large framed sheets of glass, one covering instructions for the resuscitation of persons suffering from electric shock and the other a similar public notice, both hanging close to the motor, remain undamaged.

All the fuzes in the mine (with the exception of those in one or two of the lighting circuits) were found to be intact after the accident. The fuses which blew, so far as could be judged from evidence simultaneously with the explosion, were the main fuses in the generating station. The widespread damage, however, which the in-bye cables in general suffered, taken in conjunction with the load on the generator at the time, and the size of the fuses in the generating station, would lead one to expect this to be the first result of such mechanical damage to the electrical system as would be caused by the wholesale wreckage during the continuance of the explosion.

The expert witnesses all agreed, and without reservation except in one case, in placing the point of origin in a particular length of about 60 yards in the Busty West haulage way. Attention was thus concentrated on this neighbourhood, and all the foregoing did not therefore actually come out in evidence. Of its truth, however, no doubt need be entertained. The suspected area was defined as lying between the curve on Busty West haulage way about 40 yards from downcast shaft and a point in the roadway adjacent to the 5-h.p. motor driven centrifugal pump, above referred to as the Busty straight west pump. The electric plant in this area consisted of three 7/20 rubber covered cables supported from roof and side timbers, a 6-way fuse box, a starting switch, and the pump motor itself.

The three latter items, namely, the fuse box, the switch, and the motor, were close together and at the extreme in-bye end of the suspected area. The mining experts were however unanimous in saying that the indications of force in the neighbourhood of the pump were so great as to preclude the possibility of the pump having been at, or even very close to, the actual point of origin – the damage to pipes being specifically instanced. In these circumstances the cables only remain for consideration, though it must be said that Dr. Thornton, Professor of Electrical Engineering at Armstrong College of Science, Newcastle, who was called to give expert evidence from an electrical point of view, stated in reply to a question that he thought it "quite possible" that the explosion had originated in the fuse box. Dr. Thornton argued from the condition of the box after the explosion. in conjunction with the mining expert evidence above referred to, rather than from direct evidence but other boxes in the pit were damaged as badly, and there was no evidence to show that the box in question was other than it purported to be, namely, a gas-tight box with its cover properly bolted down. At the same time Dr. Thornton drew attention to one important point: the danger of allowing an accumulation of coal dust on motor or switch terminals, and the verdict of the jury, namely, that the explosion was a coal-dust explosion pure and simple, lends point to Dr. Thornton’s warning.

With regard to the cables, the possibility that the accident was the result of mechanical damage to them is in my opinion less remote than either of the alternatives more particularly suggested for the jury’s consideration, namely, sparks from the running set or arcing due to coal dust in the fuse box. It has not been possible since the accident to completely examine the cables within the suspected area due to heavy falls of roof, but in any event the difficulty of discriminating between cause and effect in examining such a small cable as a rubber covered 7/20 wire would have been very great. There can be no doubt that a heavy fall of stone on a cable might result in an arc appearing external to that cable, and an instance was indeed quoted in evidence as having happened at this very colliery about four months before the explosion. In the event of such an arc the presence of gas or coal dust in sufficient quantity is all that may then be required to cause a serious explosion, but it must be added that no evidence exists of an occurrence of the kind in the present case.

To sum up, though electricity cannot be acquitted of suspicion in the absence of other positive cause, there is no direct evidence against it, any more than against any one of the dozen safety lamps which the evidence showed to be still unrecovered from the pit. A review of the evidence suggests one or two general considerations

R. NELSON.

April 10th, 1909.