Before the 20th century the deep coal reserves near Wrexham were inaccessible. Modern technology and access to share capital enabled Henry Dennis and his son, Henry Dyke Dennis, to develop a coal mine at Acton Grange, near Gresford. Work started in 1907 and four years later the 2,263 foot deep Dennis Shaft was complete. The first coal was raised in June 1911.
The colliery expanded rapidly and by 1934 2,200 men were working at Gresford. The colliery divided into two main sections: the Dennis and the South-East. The north end of the Dennis (the 20s & 61s districts) was worked by hand, but the other districts (the 109s, 14s & 29s) were mechanised.
The mine worked a three shift system. The night shifts were usually for repair work, but Friday and Sunday nights were coaling shifts. Miners often worked extra shifts "doubling up" even though it was illegal and on those nights, the management welcomed the extra hands.
Commercially there were problems at Gresford. The mine made a loss in 1929, 1932 and 1933. The manager, William Bonsall, was under pressure to increase productivity. Even when it made money, it was not profitable enough for Dyke Dennis and his family who owned 45% of the colliery.
Perhaps more importantly, in December 1911 the Government had passed the Coal Mines Act:
42 (1) For every seam in a mine newly opened after the commencement of this act there shall be . two main intake airways, one of which shall not be used for the haulage of coal.
This law did not apply to Gresford Colliery as it was already open, but neither did the owners follow this good practice. This was to have fatal consequences for the miners of the Dennis section on Saturday 22nd September 1934.
36 (3) Every part of the mine, in which ten or more persons are employed at the same time, must be provided with at least two ways affording means of egress to the surface.
1911 Coal Mines Act