Lewis Merthyr Colliery Explosion – Trehafod – 1956

LEWIS MERTHYR. Trehafod, Glamorganshire. 22nd. November, 1956.

The Lewis Merthyr Colliery was situated in the village of Trehafod about 18 miles from Cardiff. The winding shafts for men and materials were known as the Bertie Pit and the Trefor Pit and were sunk about 1878 but high-class steam coal had been produced for ten years before this from shafts that were still contained within the mine. There were six vertical shafts serving the mine. Of these, the House Coal shaft and the Cymmer shaft were used for pumping, the Lady shaft for ventilation and was the upcast shaft, and the Hafod shaft was the downcast and was the third means of egress. The output of the colliery was 1,250 tons per day. The mine employed 936 persons underground and 226 on the surface.

The colliery was part of the No.3 Area of the South Western Division of the National Coal Board and the principal officials were Mr. M.J. Davies, the Area General Manager, Mr. A. Hudson, Assistant Area General Manager, Mr. G. Tompkin, Area Production Manager, Mr. C.H. Hodkin, Area Production  Manager (Operations), Mr. D.N. Simpson, Deputy Area Production Manager (Planning), Mr. J. Murphy. Group Manager, Mr. A.R. Fox, the Manager who was killed in the explosion, Mr. E. Moore, Undermanager of the Trefor Pit and Mr. W. McDonald, Undermanager for the Bertie Pit.

The seams worked at the pit in descending order were the Two Feet Nine, the Six Feet and the Gelli Deg. All the seams were worked by the advancing longwall method and the coal was won by pneumatic picks and had loaded onto conveyors. The only seam affected by the explosion was the Two feet Nine which lay at 328 yards below the surface. The seam had an aggregate thickness of seven feet and contained four dirt bands of varying thickness. The roof was a good clift and the floor was of fireclay and the seam had been extensively worked in the area.

At the time of the explosion, the N4 district was the only district being worked in the Two Feet Nine seam. The coal was raised at the Trefor pit and comprised the total output of that pit which was about 320 tons per day. The district consisted of a double-unit longwall conveyor face served by two end supply roads and a centre loading road. The gradient was negligible. Each side of the face was 105 yards long. The coal was hand got with pneumatic picks and the face advanced four feet six inches on a 48-hour cycle. The coal was fulled only on the morning shift with the cycle of operations arranged so that the face conveyors were moved forward on alternating afternoons. There was a similar alteration in the waste drawing and packing operations done on the afternoon shift. The three roads were ripped on the afternoon and night shifts, the rippings being taken entirely in the roof.

Traditionally the working section of this seam had been the lower four feet of the seam with a bed of coal one foot six inches thick forming the roof and the N4 panel had been opened in this way. In September 1956, it had been decided to try to work the full thickness of the seam. By doing this no coal would be lost and better material would be obtained for the packs. By November the whole of the left-hand face was being worked to the full thickness of the seam but the right-hand face remained as originally developed.

All the machinery was driven by compressed air and no electrical power was installed in the district. On each of the three shifts, there were two deputies. One was responsible for the working face, the end roads to the junctions with the intake airway and for the centre road to its junction with the return airway. The other deputy was responsible for the intake and return roads outside these junctions. An overman was in charge of the morning shift and the night shift was similarly supervised.

The support of the left face was by Dowty hydraulic props set to heavy section corrugated steel bars. The bars were set at eight feet intervals with rows of props four feet six inches apart. Strip packs were built eight yards wide leaving wastes ten yards wide. In each waste Walton quick-release steel chocks were set along the edge of the waste. On the right-hand side of the face, where the work was carried on in the old way, the roof was carried on H-section steel props, with both ends closed, set to corrugated steel bars. Wood compression pads were used between the props and the bars. the rows of props were set at four feet six yards apart with the bars four feet apart. On the face, strip packs, five yards wide were built leaving wastes six yards wide. Opposite each waste two hardwood chocks fitted with quick-release devices were built.

The coal face at the roadhead of the centre road was kept about 12 feet in advance of the general line of the face, and the rippings were taken to the coalhead. The roof was supported by means of steel arches, 14 feet wide, set at intervals of four feet six inches to correspond with the advance of the face conveyors. These steel arches were a temporary means of support from the span of the roof, about 20 feet long, between the coal head and the permanent roadway supports, which consisted of steel arches of similar dimensions but had the straight portion of each leg cut off and a curved steel plate welded on. This rested on a soft wooden cog which formed part of the ten-yard wide roadside packs. These permanent supports were set three feet apart and the cogs were erected to the height of the face working. The end supply roads were supported in the same way but the interval between the inbye permanent support and the face did not exceed ten feet as these roadways were not advanced in front of the general line of the face.

The district was ventilated by air from the Hafod downcast shaft which returned direct to the Trefor upcast shaft. The end roads served as intakes and the centre loading road as a common return. Air measurements were made on the 5th., November, 1956 showed 7,828 cubic feet of air per minute entering the left-hand face, 7,201 cubic feet entering the right-hand face and 15,442 cubic feet returning on the centre road. Air samples showed methane content in the centre road as 0.06 per cent. The reports made by the deputies showed that inflammable gas had been found on four occasions since the district started production in February 1956. All the reports were “of blowers diluted at the point of issue” at the waste edge.

Explosives were not normally used in the district. The roof rippings in all three gate roads were got down by pneumatic picks. The only case of a shot being fired anywhere in the district was on the 16th. November 1956 when one shot was fired in the floor at the centre road. The shot was necessary to grade the road through a fault. To suppress dust the seam was systematically infused with water and this proved satisfactory. The roadways were regularly treated with limestone dust and the most recent samples taken before the explosion occurred showed the incombustible content of the dust on the floor to be 78 per cent and on the roof and sides 75 per cent.

On the night of 8/9th November 1956, an extensive fall of roof occurred in the roadhead of the centre road from the inbye permanent support practically at the face of the roadhead, a length of about 16 feet. One steel arch was left standing between the inbye end of the fall and the coal face. The cavity was the full width of the roadway and exposed the Three Coal seam some 24 feet above. For some time earlier a small fault had been working down the left-hand face towards this road. At the time of the fall this fault was less than ten yards from the left-hand side of the road. There was no evidence of the fault in the cavity but it was obvious that the thick bed of clift above the seam had changed to become weaker than normal.

The fall was cleared and 14-foot steel arches were erected beneath the cavity. these arches were covered with wood lagging which in turn was covered with a “cushion” of rubbish about four feet thick. The top of this would have been eight feet from the top of the cavity. The roof and side of the cavity above this packing were not supported in any way. The production of coal was resumed on Monday 12th. November, 1956 and work proceeded without incident until the night of the 19/20th. November when a second fall occurred in the roadhead which was an extension of the earlier fall. The cavity had now extended to the coal head and was about 30 feet long and 30 feet high. It had also widened to about 30 feet and exposed a slicken-sided slant about 10 feet to the left of the fault which was now covering the middle of the road and there had been no previous indication of this slant.

This second fall made coal production impossible and this was the state of affairs on the 21st. November. By the afternoon shift of this day, the fall had been cleared and the erection of steel arches under the cavity commenced. This work was being carried out on the night shift when at about 3 a.m. on the 22nd of November, four of the six newly erected steel arches were displaced by a stone weighing about three tons which fell from the cavity. The colliery manager accompanied by the morning shift overman arrived at the colliery at about 5.30 a.m. He decided to erect an “umbrella” of ten feet arches covered by wooden lagging beneath the gate of the conveyor could run. These arches were erected without disturbing the 14-feet arches displaced by the fall. The stone that had fallen was broken up by pneumatic picks and the work of erecting the arches began. By this time the men employed in the morning shift had begun to reach the meeting station at the junction of the left-hand supply road with the intake airway. A few of these men were brought forward to assist with the work and the remainder told to stay at the meeting station until they received further instructions. The men at the meeting station noticed a “puff” of wind and a cloud of dust. A collier who had passed into the left-hand face returned to say that he had seen flame in the centre road. The work of rescue was quickly organised.

Those killed:

• E. Howells aged 37 years, turbine attendant
• S. Thomas aged 69 years, overman.

Those fatally injured:

• A. Atkins aged 40 years, collier
• T. Davies aged 38 years, chargeman
• A.R. Fox aged 41 years, the manager
• C. Jones aged 36 years, overman
• R. Jones aged 57 years, repairer
• A.H. Mills aged 35 years, repairer
• P. Profitt aged 27 years, repairer

Those injured:

• H. Bryant aged 46 years, chargemen
• W. Childs aged 43 years, repairer
• F. Crump aged 39 years, repairer
• W.H. Davies aged 50 years, packer
• I. Humphries aged 35 years, deputy

The inquiry into the causes and circumstances attending the explosion which occurred at the Lewis Merthyr Colliery, Glamorganshire, on 22nd. November 1956, was conducted by T.A. Jones, O.B.E., H.M. Divisional Inspector of Mines and reported to the Right Honourable Lord Mills, K.B.E., Minister of Power on the 8th. November 1957.

The inquest was conducted by H.M. Coroner for North Glamorgan, Mr. T. Alwyn John on 1st. March 1957, who sat with a jury. A verdict was recorded an all nine men who died that:

They had died as a result of burns accidentally received in an explosion at the roadhead of the centre road in the N4 district of the Two Feet Nine Seam at Lewis Merthyr Colliery on the 22nd. November 1956.

From all the evidence it was concluded that an explosion of firedamp had taken place in and beneath the cavity. The flame had travelled about 70 yards outbye along the centre road, for about 15 yards along the left-hand face and 25 yards along the right-hand face. The severe nature of the burns that the men received suggested that the flames had persisted for some time in the vicinity of the cavity. There was no sign of violence and no indication that coal dust had played a part in the disaster.

Tests were made to determine the source of the firedamp and it was found that there was 80 per cent firedamp at the top of the cavity although the presence of gas had not been detected prior to the explosion. Immediately after the fall on 20th. November, the undermanager and the deputy climbed up on the debris and examined the top of the cavity and found it clear. At this time the mound of debris was deflecting the air into the cavity. No steps were taken to direct and air current into the upper part of the cavity and when the fall was finally cleared the cavity was left entirely unventilated and could not be examined. About two hours after the explosion, the night shift deputy stood on the tops of the steel arches and tested for gas as high as he could reach but this was about 15 feet from the floor and 18 feet from the top of the cavity.

All possible means of ignition were investigated and it was concluded that none of the safety or electric lamps in use at the time could have been responsible. After the explosion, it was found that the compressed air hose from the manifold of the centre road to the turbine on the right side of the face conveyor was found to be leaking from a hole but this was dismissed as a source of ignition. Except for two mining telephones, electricity was not used in the district and it was disclosed, in evidence, that the telephones had not been in circuit for some days before the explosion. Nothing was found to suggest that the explosion was caused by contraband and the only possible source of ignition that was left was frictional heating.

There was definite evidence that none of the conveyors had run during the night and the survivors stated that the explosion was coincident with the fall of the roof. This led to a careful examination of the possibility of incentive spark being produced by the fall. The tests did not produce conclusive results but it was considered that this was the source of ignition.

Mr. Jones came to the following conclusions:

1). After the fall had been cleared and while the steel arches were being erected, the upper part of the cavity contained a high concentration of methane.

2). The stone falling from near the top of the cavity brought down enough methane to produce an explosive mixture at the horizon of the steel arches.

3). The impact of the stone striking the steel arches produced an incentive spark which ignited the explosive mixture, whereupon the flame spread to the extent described earlier in this report and persisted until all the methane was consumed.

REFERENCES
The report of the causes and the circumstances attending the explosion which occurred at the Lewis Merthyr Colliery, Glamorganshire on the 22nd November 1956 by T.A. Jones, O.B.E., H.M. Divisional Inspector of Mines.
Colliery Guardian, 14th. March 1956, p.255, 12th. November, p.743.

Information supplied by Ian Winstanley and the Coal Mining History Resource Centre.