Abergele rail disaster

The Abergele rail disaster, which took place near Abergele, North Wales, in August 1868, was the worst railway disaster in Great Britain up till then.

The Irish Mail train was on its way from London to Holyhead, when a complicated shunting operation caused the derailment of a goods train at Llanddulas, the nearest sidings to Abergele, blocking the main line. In the confusion, a brake-van and six wagons loaded with paraffin were left uncoupled on a gradient leading down to Abergele, and a collision with other carriages caused it to run downhill into the path of the Irish Mail, exploding on impact.

Wikipedia