The Gresford Colliery was owned by the United Westminster Wrexham Collieries, Limited and was at the village of Gresford about two and half miles to the north of Wrexham. The mine had two shafts the downcast which was known as the 'Dennis' and the upcast which was called the 'Martin'. Coal was wound at the Dennis and materials down the Martin shaft. Men were raised and lowered in both shafts. The sinking of the shafts started in 1908 and coal was first wound in June, 1911 so that it was not 'newly opened' within the provisions of the Coal Mines Act, 1911 and the provision that there must be two intake roadways from each seam did not apply to the colliery.
The mine employed about 2,200 persons, 1,850 below ground and 350 at the surface. Three seams were worked at the colliery. They were the Main, Crank and Brassey but by the time of the explosion the workings in the latter were idle. The Dennis section of the Main Seam, in which the explosion occurred, was made up of five districts each worked on the longwall system. These sections were known as 20's, 61's, 109's (which included 92's), 14's and 29's and employed 280 men on the day shift, 240 on the afternoon shift and 195 on the night shift.
Coal was got and wound on the morning and afternoon shifts and some coal was wound on Friday and Saturday nights. The packs and faces were moved during the night shift. The weekly output of coal from each of the Districts during the ten weeks prior to the explosion were 928 tons from the 20's, 732 from the 61's, 813 from the 109's, 1,617 from the 14's and 1,340 from the 29's.
Mr. William Bonsall, the manager had occupied that position since 1917 and for three years previous to that he had been assistant manager to Mr. Groves. Previous to that he had been a deputy for three years, an overman for three years and undermanager for two years at Swanwick Colliery, Derbyshire. Before that he had worked for nine years as a filler, holer and contractor at Pinxton and Cotes Park Collieries and for four years as a haulage hand at Birchwood Colliery, all in Derbyshire.
Until two years before the explosion there was also an agent, Mr. T.H. Cockin but that office had not been filled and Mr. Bonsall was left to work the mine without guidance from any technically informed official. He visited the several districts in the Dennis Section from time to time but before the explosion, he had spent most of his time in the South-East Section where belt conveyors were being installed. He had been underground during the night shift but it was so long ago, that it emerged at the inquiry, he could not remember when it was.
For many years Mr. Thomas Hughes was undermanager but in 1933, he fell sick and Mr. Edward Alan Roberts acted in his place. After January, 1934, there were two undermanagers, Mr. Edward Alan Roberts and Mr. Andrew Williams, Mr. Roberts supervised the South-East and No.1 North Section of the Main Coal Seam and the Crank and Brassey Seams and Mr. Williams the Dennis Section of the Main Coal Seam. Since 1914, Mr. Roberts had been employed as an overman at the colliery.
Before 1934, Mr. Williams was not employed at the colliery but, up to nine years before he had been employed at the Hafod Colliery for 24 years. The Hafod Colliery was sunk in the 1860s and originally called the Ruabon New Colliery. During the time he was not in the North Wales Coalfield he was the manager of the Blaenhirwaun Colliery in Carmarthenshire. Supervising only the Dennis Section,
Mr. Williams was underground daily but not at night. He arrived at the pit about 5 a.m. each day and left about 5.30 p.m. but very often returned to the pit. He was underground during the night shift of the 27 th April to see repairers working on the 142's deep and on the night shift of the 7 th August he visited the face of the 14's district to see how a newly installed coal cutting machine was working.
Electrical power was used for coal cutting and conveying and the chief electrician at the colliery was Mr. Josiah Ernest Hague. Mr. Sydney Erwin Hayes was the Colliery surveyor and he was assisted by Mr. William Idris Cuffin who was also given additional duties under the manager's directions for taking air measurements and the collection of dust samples. There were three overmen on each shift but only one of these, Mr. Frederick John Davies on the night shift, exercised any supervision in the Dennis Section and that only occasionally. Previous to the explosion, the last time he had been at the face of any of the workings in the Dennis Section was on the 21 st August when he went along the face of the 14's District. Some time during August he had been along the face of 29's district and on the 19 th August he was in 20's district but did not visit the face. In June he had been in 23's face and 109's district and in March he went round the 95's district and in two or three faces on the 20's district. At the inquiry Mr. Davies stated that he devoted his time to the South-East Section of the Main Coal Seam and only went into the Dennis now and again. This meant that, except for the time that Mr. Andrew Williams, undermanager of the Dennis Section, was underground, that section of the mines was supervised by 15 deputies. They were Richard Owen, T.B. Tune and William Salisbury in the 20's, J.T. Jones, W. Swinnerton and William Salisbury agent, in the 61's, N. Parry, R.T. Edwards and S. Matthews in the 109's, J.H. Thomas, H. Amos and R. Jones in the 14's and H, Thomas, W. Davies and D. Jones in the 29's on the Day, Afternoon and nights shifts respectively. The remaining deputy, Edwin Chester was employed on the night shift when he supervised men in the drift at the inbye end of the Dennis main haulage road beyond the 'Clutch' and travelled and reported on that haulage road and the Martin return airway.
Three phase current at 3,300 volts was taken down the Dennis shaft to two transformers at the bottom of the shaft where the voltage was reduced to 570 volts to work the haulage engines, coal cutting machines and conveyors. Each transformer was connected to a separate switch board. The lighting at the pit bottom was supplied from a small transformer at 110 volts. There was one main cable installed in the Dennis main intake airway which carried the whole of the current inbye for the section. The cable was controlled at its origin by a switch and fuse. Some of the coal cutting machines and conveyors were certified flameproof but others of another design were used which were supposed to be flameproof. The bells were certified flameproof but the magneto telephones were neither intrinsically safe nor in flameproof casings.
The haulage in the Dennis Main Intake and 142's Deep was by endless rope driven by an electric motor placed near the Dennis shaft bottom. The districts generally had main rope haulage driven by electricity and compressed air.
The mine was generally dry but there was a pump for pumping water from the Dennis shaft sump to the Martin shaft sump and a lodgement pump at 500 feet from the surface between the two shafts and a small pump for emptying the Martin sump into tanks in the cages in that shaft and wound to the pit bank.
Thirty electric lamps were used by the electricians but most of the lamps were flame lamps of the Prestwich Patent Protector Type. The ventilation was produced by a double inlet Walker fan placed at the surface and steam driven. There was no proper air lock at the top of the upcast, Martin shaft. Platforms called 'butterfly boards' or 'policemen', raised by the cages as they came up were relied on to prevent the air from flowing directly from the surface to the fan.