Mining has always been especially dangerous, because of explosions, roof cave-ins, and the difficulty of underground rescue. The worst single disaster in British coal mining history was at Senghenydd in the South Wales coalfield. On the morning of 14 October 1913 an explosion and subsequent fire killed 436 men and boys. Only 72 bodies were recovered. It followed a series of many extensive Mining accidents in the late 19th century, such as The Oaks explosion of 1866 and the Hartley Colliery Disaster of 1862. Most of the explosions were caused by firedamp ignitions followed by coal dust explosions. At Hartley there was no explosion, but the miners entombed when the single shaft was blocked by a broken cast iron beam from the haulage engine.