The No. 28 district in the Low Main seam where the explosion occurred is at a depth of 580 yards. The coal is 3 feet 3 inches thick with a medium clunch floor, and a roof consisting of 9 inches of clunch, 4 inches to 6 inches of coal, and 35 feet of grey bind with 60 feet of sandstone above. There is a variable but thin section of sandy material between the grey bind and the sandstone.

A double unit coal face, 280 yards long, known as 30's face (see Plan No. 1), had been advanced 1,250 yards to the north-west, rising at about 1 in 100, by orthodox machine cutting, blasting, and hand loading on to a face conveyor belt.

There were three roads (gates) to this face, the middle and right side gates being intake airways and the left side gate being the return airway. The middle gate was also the loader and conveyor gate. Electricity was used to operate the machinery in this district.

On 11th June, 1956, at a point 120 yards inbye from the junction of 30's loader gate and old 28's face trunk road, a scouring was started from 30's loader gate, driven through the waste to 30's right side gate, and for a further 15 yards to the solid coal on the right of 30's right side gate. In the coal this road, about 12 feet wide, was continued for 10 feet; then the face was widened to 30 feet and the road, still 12 feet wide, was carried forward with stone packs about 9 feet wide on each side. It was dipping at about 1 in 8 and was supported by steel arches 12 feet wide and 9 feet high. It was ventilated by an auxiliary fan 18 inches in diameter, driven by a 5 H.P. electric motor, forcing air through canvas ducting to the face. By 14th July, 1956, this road had reached a point 63 yards from 30's right side gate where it was stopped.

A coal face, now called Old 28's face, had been worked to the north-east but had been abandoned owing to difficulties in maintaining the roads. It was intended to develop a new face to replace Old 28's face advancing in the same direction-to the north-east-but leaving solid coal 80 yards wide between the ends of Old and New 28's faces and also 50 yards of solid coal to the right of 30's right side gate to protect this gate from damage. Plans were changed two or three times, both as to layout and direction of advance of New 28's face and also as to ventilation. Eventually it was decided to open New 28's face, 150 yards long, immediately to the right of 30's right side gate, leaving no coal for protection of this road and extending to the left of the original development road. This face was opened out by driving a place in the coal 12 feet wide from the left side of the developing road for 150 yards to the northwest-in the same direction as 30's face-and then making a connection through the pack back into 30's right side gate. This was completed on 29th December, 1956, and thus 28's new face was arranged to be ventilated with the original development road at the right end as intake, with the air passing along 28's face to the return gate at the left end and then in 30's right gate to 30's face, along 30's face and out along 30's left gate as return airway. Thus from the start 28's and 30's faces were ventilated in series, a matter on which comment will be made later (see Plan No. 1). At this time the Coal Mines Act, 1911, was still in force and therefore also the Electrical Regulations under that Act. Regulation 119 required notice to be given of intention to introduce apparatus into any mine or into any ventilating district in any mine, but in this case 30's and 28's districts were parts of the same ventilating district and electricity was already in use in that ventilating district.

After 28's face had been advanced 10 feet by hand getting, an Anderton shearer coal getter loader, mounted on an armoured chain conveyor, both electrically driven, was installed with what is known as a prop-free front method of support to allow the conveyor to be advanced broadside following each cut of 20 inches by which the face was advanced.

The roof at the face was supported by coupled 3 feet 3 inches long bars set to a triangular system on hydraulic props fitted with castellated heads. The system, for which the necessary authorisations and exemptions had been granted under the provisions of the Coal and Other Mines (Support) Regulations, 1956, required rows of coupled bars to be set at maximum intervals of 3 feet with 6 feet maximum intervals between props in the same row. The maximum interval between the front row of props and the face was authorised to exceed 3 feet but not to exceed 5½ feet. Alternate bars were to be advanced after each 20 inches cut.

The original development road was both intake airway and loader gate with the face conveyor discharging into a stage loader and then into the gate conveyor which extended to a common trunk road conveyor at the junction with 30's face loader gate (see Plan No. 2 which shows also the equipment and locations of the men in the district when the event occurred).

To enable the original development road to function as loader gate it was necessary at the face to remove the 3 yards wide pack on the left side of this gate to allow the face conveyor and its driving machinery to be advanced after each 20 inches cut. This road side pack was rebuilt behind the face conveyor after each day's coal getting, the original road having to be remade by taking up the floor and ripping the roof and putting in new steel arches, 12 feet wide and 9 feet high.

The return gate at the left side of 28's face was also roof ripped and packed on each side as the coal face advanced. 12 feet by 9 feet steel arches were set 3 feet apart, but within 20 feet or so of the face a smaller size of arch was used.

For the first 15 feet of advance of the coal face with the Anderton shearer, strip packs, 3 yards wide, were built 9 yards apart in the waste between the two end gates. In addition, three pre-fabricated steel chocks were set along the edges of the face working adjoining each waste. At this stage the face itself was turned a little by taking some taper cuts starting with 10 inches at the loader gate and finishing with 20 inches at the return gate.

The manager at that time (Mr. E. Maiden) had informed the Inspector for the District that he intended to stop the intermediate packs once the face had advanced sufficiently far to establish proper control of the roof. The full caving system extending from the left side pack, 9 feet wide, of the loader gate to the right side pack of the return gate, a distance of about 130 yards. was started on 11th February, 1957, and was continued up to the time of the accident,. during which time the coal face advanced a further 44 feet.

The management claimed that full caving between the roadside packs was introduced earlier than was originally intended because the roof in the wastes between the intermediate packs was not breaking down regularly to provide packing material. The waste edge support by chocks was doubled and the roof at the face improved.

The loader gate was already difficult, because of the need to take out the 3 yards wide left side pack to enable the face conveyor and its driving machinery to discharge through to the stage loader and to rebuild it behind the conveyor. As might have been expected, these difficulties became much more serious after full caving was started. Indeed, large falls of roof occurred on the loader gate and continued as the coal face was advanced. The road itself was widened to 17 feet by extending it on the left side as the cavity left by falls of roof widened on this side. To cover this width 5-feet long horizontal joists were inserted between the steel arch sections. For several days before and also between 6 and 7 a.m. on the morning of the explosion falls had occurred and had left a cavity about 36 feet long, 9 to 12 feet wide, and 10 to 12 feet high, above the steel arches in the roadhead. The top and sides of this large cavity were only partly, and quite inadequately, secured by two chocks of wood built on the wood lagging pieces laid over the steel arches. Persons had to work at the face under the edge of this cavity and the electric motor and cables for the driving gear of the face conveyor were under it with only the steel arches covered by boards to protect them against danger from further falls from top or sides of the cavity. Indeed, the fall which occurred between 6 and 7 a.m. on 21st February partly buried the face conveyor engine and closed access to the coal face, so that the miners had to be withdrawn for a time, and under the supervision of the under-manager and deputy they helped to remove enough of the debris to enable the face conveyor to run again.

This fall was liable to damage the machinery, including electrical gear, in the roadhead. I shall refer later to the protection required by the Coal and Other Mines (Electricity) Regulations, 1956. The fall was also liable to cause injury to workmen, especially as the top and sides of the cavity were insufficiently secured before this fall took place; with this fall, steel arches, horsehead girders and covering timber were displaced and one of the chocks fell out leaving the cavity with even less support to the top and sides. An electrician and a fitter, who were there at the time, say that they examined the machinery and found no damage. They agreed that it was safe to restart the face conveyor and full scale working was resumed at the face without anything being done to secure the top and sides of the cavity.

Regulation 12 of the Coal and Other Mines (Support) Regulations, 1956, requires that "if any fall of roof or side involving the displacement or breakage of any support has occurred at a place where any person has to work or pass, it shall be the duty of the person for the time being in charge of that part of' the mine forthwith to ensure that any roof or side exposed thereby is, if necessary, dressed and is secured by supports and that any such dressing and securing is done before any work of clearing debris is begun, other than such work of clearing debris as is necessary for the setting of the supports ".

It was under these conditions that the explosion occurred on the morning of 21st February. Plan No. 3 shows 28's loader gate roadhead and the cavity. above the steel arches from which the stone fell on to the terminal box of the conveyor motor.