0.—2

40

Waipa Mine. —On the Ist September a serious fire was discovered in the return airway where itpasses the underground stables. Its spread was successfully prevented by enclosing it by means of temporary wooden stoppings. On the sth an unsuccessful attempt was made to recover the return airway, but this failed, and two of the stoppings were advanced to permit of a new return being used in place of the part of the old return enclosed in the fire area. The fire was not effectively sealed off till the 12th, after which work in the mine could be resumed. The temporary stoppings were later replaced by brick stoppings. Denniston Mine.—For a considerable time prior to October trouble had been experienced through heating in the old wide and high bords to the rise of No. 8 section of the Cascade Mine. iSome of these bords were over 20 ft. in width and about the same in height, and the pillars on each side were small and broken, with the result that it was almost impossible to erect effective stoppings. The old rise workings were sealed off on account of fires, and the fires were close to the stoppings sealing off these workings from No. 8 section. On the 20th October the fire broke through, and a large portion of No. 8 section had to be sealed off and abandoned. It will be noted that all the dangerous occurrences during the past year have been underground fires. These fires were almost entirely due to the bad methods of mining practised during the early days of these mines, and not to the workings of recent years. The principal defect in the old workings was the inadequate size of the pillars. After standing for many years these small pillars tend to crush, and the crushing results in fires, which have to be sealed off, with the consequent abandonment of areas, some of considerable extent, from which only a small percentage of the coal had been extracted. During the past year an investigation has been made by the officers of the Department into the percentage of coal lost at various mines. At one mine on the West Coast of the coal originally present in the now abandoned workings 45 per cent, only was extracted ; from another large mine in the same district the coal extracted amounts to approximately 40 per cent, of what was originally available. From both of these mines better methods of working would have enabled at least 65 per cent, of the coal available to have been extracted. An investigation of the old mines in the Waikato which have been shut down or worked'out and abandoned shows that the coal lost in that district has been enormous. If allowance be made for a 3-chain barrier which would have to be left between the abandoned workings of these mines and the workings of a new mine starting in the vicinity of any one of them, it appears that the highest extraction was only 35 per cent., and the lowest under 15 per cent., and that the average extraction was under 20 per cent, of the coal originally present in the areas now abandoned. The Waikato seams are thick and have generally a bad roof, so that a very high percentage extraction is not to be expected, but even with the thick seam and bad roof an extraction of over 50 per cent, should have been attained. In the early days of the field the market value of the coal produced did not permit of efficient methods of working, but improper methods were carried on with, no doubt, a temporary advantage to the mining company, but at a serious final loss. Ultimately the bad methods of working caused fires, and consequent high cost of working, with the forced abandonment of profitable areas of coal only partially worked, and finally led to the closing-up of the mines. During the past year the Inspectors, in their respective districts, have endeavoured with some success to get still better mining methods practised, both on the grounds of increased safety and increased economy. In several instances the size of pillar adopted has been increased, which should reduce the tendency to fire, and in some mines the panel system or a modification thereof has been adopted with a view to enabling any underground fire that breaks out to be safely and expeditiously dealt with and prevented from involving more than a limited area of the mine. The Inspectors have personally assisted at mine-fires and given assistance acknowledged, by the company concerned, to have been of value. (e.) Electricity at Collieries. (Regulation 160.) During 1924 there has been a further increase in the number or capacity of electrical installations. The following is a summary of the annual returns, in accordance with Regulation 160 (c), regarding electrical apparatus at collieries : — Number of collieries at which electrical apparatus is installed .. .. 21 Number of continuous-current installations .. .. .. 12 Number of alternating-current installations .. .. .. . . 10 Number of collieries electrically lighted .. .. .. . . 18 Number of collieries using electrical ventilating-machines . . . . 14 Number of collieries using electrical pumping plants .. .. .. 13 Number of collieries using electrical haulage plants . . .. . . 14 Number of collieries using electrical screening plants . . . 5 Number of collieries using electrical miscellaneous plants . . .. 8 Number of collieries using electrical locomotives .. .. .. 1 Total horse-power employed from motors on surface .. .. .. 3,109^Total horse-power employed from motors below ground .. .. .. 1,817§