The South Wales coalfield occupies a unique place in the history of the British labor movement. These coalfields, which stretched from Pontypool, near the English border, to the Welsh-speaking heartlands of Swansea and Llanelli, were at one point one of the largest coal-producing areas in the world. Rhondda Valley, perhaps the most famous site, produced an astonishing 56.8 million tons of coal in 1914, or 19.7 percent of all of Britain’s coal output.

These incredible levels of productivity were won at a cost: deep coal mining remains one of the most dangerous professions in the world. South Wales coal in particular is extremely difficult to mine, owing to its dry, gaseous nature, which makes it prone to explosion, as the grim list of mining disasters illustrates. Second, the region contains numerous geological faults, which make coal inaccessible behind layers of rock and shale. Describing these conditions in 1922, one Rhondda miner painted a vivid picture of the dangers workers faced:

Away from the sunlight and fresh air, sometimes in a temperature of up to 90°C, every movement of the day, inhaling coal and shale dust, perspiring so abnormally (usually as few men in other industries can realise) head throbbing with the almost inhuman exertion . . . the roof perhaps 18 inches low, perhaps 20 feet high, ears constantly strained for movements in the strata on which his limbs or his life is dependent.