61913 Senghenydd Colliery accident (United Kingdom, 439 casualties)
A mine known as the Senghenydd Colliery, in southern Wales, experienced the worst accident ever on UK soil. The accident took place October 14, 1913 and ended with 439 lives taken. This explosion was started by the firedamp ignition in the electric bell signaling gear. This ignition ended up igniting the coal dust and gasses, which then traveled through most of the subsurface tunnels.