Tower, Hirwaun, Glamorganshire. 12th April, 1962
At the No.1 upcast shaft a Sirocco single inlet fan produced 95,000 cubic feet of air per minute at a water gauge of 4.1 inches and at the No. 4 upcast shaft a similar fan produced 180,000 cubic feet of air per minute at a water gauge of 2.8 inches.
The Tower Colliery was in the No. 4 Area of the National Coal Board’s South Western Division and was situated at the village of Hirwaun about four miles from Aberdare. The seams that the colliery worked were close to the bottom of the coal measures and it was centrally placed along the northern outcrop of the coalfield.
Records showed that coal was first mined in 1864. The ‘take’ of the colliery traversed three large faults which naturally divided the mine into three parts. The natural division and a scheme of reorganisation and modernisation had resulted in the mine being served by six cross measure drifts from the surface and three vertical shafts. The colliery produced about 1,500 tons a day and employed 938 men underground and 234 at the surface.
The ventilation was produced by two fans.
Safety lamps were used throughout the mine. For general lighting the Oldham Wheat W type electric lamp was used. Senior officials and deputies used Thomas and Williams Cambrian type No.8 flame safety lamps and Thomas and Williams type No.1 flame lamps were used as gas detectors by appointed workmen. The seams that had been worked in the life of the colliery in descending order were the Four feet, the Six Feet, the Red Vein, the Nine Feet, the Bute, the Seven Feet and Five feet. At the time of the explosion the Nine Feet, Seven Feet and Five Feet Seams were being worked.
Mr T. Wright was the Area General Manger, Mr. P.R. Weekes the Area Production Manager, Mr. V. Lewis, the Deputy Area Production Manager (Operations), Mr. S. Thomas the Deputy Area Production Manager (Planning) and Mr. T.G. Jones the Group Manager. The Manager of the colliery was Mr. J. T. Ryder and there were three Under managers of whom Mr. C.J. Bell was responsible for the area affected by the explosion.
This part of the mine was known as ‘Tower 4’ and was served by the No.3 Drift and the No. 3 New Drift and intake airways and the No. 4 upcast shaft. It was known as the ‘G’ panel and was in the nine Feet Seam.
The ‘G’ panel was developed following the establishment of a new ventilation circuit of which the No. 3 New Drift formed the main intake with a main return airway by way of a crossmeasure driven to the No. 4 upcast shaft. From these main airways, two levels at 30 yard centres were driven on the strike of the seam to the limit line of the working 850 yards inbye. In this area the Nine Feet Seam was found to vary little in thickness, 7 feet 6 inches, with a strong clift roof and a hard fireclay floor. At the time of the explosion there were two working places in the panel. One to the dip from the levels and worked by a Continuous Miner and was called the ‘Miner’ heading which was not affected by the disaster. The second working place was developed near the inbye end of the levels to the rise. This heading was known as MC3 which was the area where the explosion occurred.
The panel was under the supervision of an overman and a deputy on the morning shift and on the afternoon and night shifts by deputies and the assistance of an overmen who also had responsibility for other districts. On each shift there was a shotfirer and a second official with the status of deputy was employed in the ‘Tower 4’ part of the colliery to closely supervise the arrangements for the ventilation of the several narrow drivages.
The MC3 heading had been driven at a rising gradient 1 in 10.5 in the full thickness of the seam for 328 feet and was 12 yards wide. The coal was won by shotfiring out of the solid coal and loaded on to a short scraper chain conveyor by a Sampson MC3 Loader.
The conveyor delivered the coal to a belt conveyor down the heading which in turn fed the main gate belt conveyor in the return level. Coal was worked on each of the three shifts. The support in the heading was by straight H section girders, 6 inches by 5 inches, carried on wood props set at the road sides.
All the machinery in the heading was electrically driven and supplied from a 300 kVA 3300/550 volt flameproof transformer in a substation in the ‘G’ return roadway about 500 yards outbye of the MC3 heading. The neutral point of the 550 volts winding was earthed. On the primary side of the transformer there was an oil-immersed circuit breaker which was fitted with time-lagged overload trips set at 50 amps and an instantaneous earth leakage device connected to a current transformer in the secondary neutral lead. This was arranged to trip the circuit breaker when a current of 2.5 amps flowed from phase to earth in the 550 volt system.
The secondary side of the transformer was connect by a short length of .15 square inch paper insulated, lead covered, double wire, armoured cable to a flameproof airbreak section switch in the same substation. This switch was provided with an isolator and a hand operated circuit breaker, and was fitted with thermal overload trips set at 142 amps, instantaneous earth leakage device designed to trip when a current of 3.5 amps flowed from phase to earth. The earth leakage devices were designed to trip and lock out automatically the respective switches on the occurrence of an earth fault on the
550 volts system and to indicate, by means of a visible flag, that a fault had occurred. A test button was also provided on each switch so that the correct functioning of the devices could be tested.
An armoured cable from the section switch passed inbye along the return to a flameproof gate end switch controlling the ‘Miner’ heading conveyor. The supply was looped through the busbars of this switch to a coupling box from which the ‘Miner’ was supplied and the cable continued to the MC3 heading and a flameproof gate end switch controlled an auxiliary fan and the MC3 belt conveyor. Both these switched were in the return roadway a few yards from the entrance to the MC3 loader. From the last switch the cable passed up the heading to two coupled gate end switches placed 20 yards back from the face. One of these switches controlled the scraper chain conveyor and the other the MC3 loader. The feeder cable was connected at the end of the busbars of these switches and was looped back on itself.
The MC3 heading was ventilated by a 16 inch diameter Meco axial flow auxiliary fan which forced the air from the intake level through ducting which was 20 inches in diameter. The fan was in the connection between the intake and the return levels about 12 yards outbye of the MC3 heading. The manager had set a minimum quantity of 2,100 c.f.m. to be delivered to the face.