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Electricity. — At an early stage of the investigations the electric cable in the Harvey Seam was looked upon with suspicion as a very probable cause of the explosion, and when it was found that one of the three cores was faulty, this suspicion was intensified. The cable consisted of a three-core single armoured cable suspended at suitable points by straps fixed to props near the roof by pieces of tarred cord, except in two cases where iron straps were bolted to iron eye-bolts knocked into holes in the roof. When it was found that there was a fault on one of the cores, the cable was cut in the shaft sidings, and at other points, with a view to discovering its whereabouts; finally, the fault was found to he under a large fall about 120 yards long, commencing 180 yards beyond the Drift Way end. The exact point was subsequently located, and on ridding down to the cable it was found that an iron spike, such as is used for nailing down crossings, had penetrated through the armouring and come in contact with one of the cores. The spike was one of several which had been used for fastening an iron plate 2 inches by ¼ inch thick by 6 feet long on to a piece of wood, in order to form a skeating for a curve on some endless-rope haulage which had been in operation many years previously. As no one remembered having seen this piece of wood with the iron plate lying about, it is probable that it had been used as "lofting" on some balks, and had been blown by the force of the explosion, and had lain on the floor with the spike points protruding an inch through the wood and pointing upwards. When in this position the fall had taken place which brought down the cable, and one of the spikes entered the armouring as before mentioned. A short length of the cable containing the damaged portion was cut out, but a most minute and microscopic examination of both the nail and the hole it had made failed to show the slightest sign of burning or arcing, and it was quite evident that the fall was a result of the explosion, and the spike had entered the cable after the current had been cut off, when the shaft cable was severed further outbye. A further examination of the haulage road proved that the direction of the explosion was from inbye out towards this long fall, and by following up this evidence it was possible to piece together portions of props and balks which had been broken and part of them blown outbye. This was done in a large number of cases, the distance from the half prop or balk which had been left standing varying from one to six yards. Up to a certain point on the haulage road the direction as to force was constant, and no contradictory evidence of this kind was found. At a point 111 yards on the outbye side of the 3rd North Way end the direction of force at once changed, and the evidence of broken and displaced timber was uniformly in the opposite direction. The heavy balks at the 3rd North Way end showing this in a very marked degree. It appeared at first to be more than a coincidence that at the very point where this change in direction of force occurred there should also be a joint-box in the cable which had been suspended from the roof by iron hangers. An external examination of the box and a careful inspection of the cable for 100 yards on either side showed that there was apparently nothing wrong with box or cable. The cable was afterwards cut 5 feet on each side of the box and tested, but nothing wrong could be found with it. The box with the cut-off portion of the cable was then taken to the surface and carefully examined by Mr. R. Nelson, H.M. Electrical Inspector of Mines, and finally a pressure of 2,500 volts was passed through it for ten minutes, without disclosing any fault whatever. The box was then opened, and the bituminous compound cleaned out (the box was not quite full of compound). but the most minute examination did not show anything wrong with it. There was no trace whatever of burning or arcing. We are therefore of the opinion that the joint-box could not have been the source of the explosion.

A circumstance was brought to our notice which at one time led us to think that possibly a similar occurrence at Auckland Park might account for the origin of the explosion. This incident occurred at Black Boy Colliery, belonging to the same firm. One morning in the summer of 1912 — prior to the explosion at Auckland Park — the foreshift men at this colliery were walking inbye when they saw a sudden burst of flame from a joint-box in the Hutton Seam landing, and at the same time the main electrical supply failed. An examination of the box showed that there was a small hole at one side of the filler cap, but whether it had there before the burst or was caused by it was not determined. The roof immediately above the hole was splattered with the bituminous compound, and a large sooty streak extended from the box right across the roof of the roadway. This was evidently the result of the escape of bituminous vapour at the horizontal joint, which was formed of round packing would not offer any great resistance to a sudden internal rise of pressure. (It should be remarked the joint-boxes at Auckland Park were of a much stronger pattern than those at Black Boy, and it is probable that under similar conditions sufficient vent might be obtained at the joint without bursting the box.) On the box at Black Boy being opened it was found that the cause of the breakdown was a loose terminal screw. Very little bitumen had been lost, and there was no sign of arcing on the terminals. Other circumstances of interest were (1) the pit bottom fuses did not blow ; (2) the cable was live but no motor was running; (3) the joint-box only broke down, as will be seen directly, under abnormal conditions. Black Boy, Auckland Park and Shildon Lodge Collieries are all coupled together electrically, the common supply being generated at Auckland Park. The cause of the flashing from the joint box at Black Boy Colliery was afterwards found to have been the result of some water from a three-way tap in a motor house at Auckland Park being accidentally allowed to impinge on a live lead at a switchboard. This caused a dead earth and a sudden rise in pressure, which found vent at the joint-box in Black Boy Colliery. The bituminous compound in the joint-box would, by a sudden rise in temperature, be readily converted into an inflammable vapour, and possibly very little sparking would be sufficient to ignite this vapour.

It is worthy of remark that a case of an explosion of vapour given off by heat from bituminous compound recently occurred in connection with a lighting installation in a dwelling-house at Hebburn.

As previously pointed out, a close examination of the interior of the joint-box at Auckland Park gave no evidence of any defect or arcing. The case at Black Boy is important as confirmation that a joint-box is the weakest part in an electric circuit, and probably if no one had witnessed the occurrence at Black Boy the flashing would never have been suspected. If flashing such as took place in the landing at Black Boy on a longwall road, where there was little or no coal dust, had occurred at the joint-box on the Main Engine Plane at Auckland Park, there would have been little difficulty in accounting for the explosion.