An explosion tore through the Dennis section of Gresford Colliery, near Wrexham, at about 2 a.m. on 22 September 1934. It started an underground fire and trapped hundreds of men. Six escaped from the affected workings. Most did not.

The Friday night shift was particularly busy. Wrexham were due to play Tranmere Rovers on Saturday afternoon, and some miners had worked extra or exchanged shifts so they could attend the match. In the Dennis section, 261 men were killed.

Rescue teams entered the mine after the explosion, but conditions underground were dangerous. Three rescuers died from carbon monoxide. The fire continued to burn, and the risk of gas and further explosions increased. By the following evening, with no prospect that anyone remained alive, the decision was made to seal the shafts.

Most of the dead could not be recovered. The disaster eventually claimed 266 lives, including a surface worker killed by debris from a later explosion.

An official inquiry opened the following month. Its report, published in 1937, did not establish a definitive cause for the original explosion. Evidence nevertheless raised serious questions about conditions and management at the colliery. Records held by The National Archives include a statement from an assistant surveyor who said that air measurements entered before the disaster had been invented on the instructions of mine manager William Bonsall.

For many families, another question remained unresolved. Their relatives were still underground. Emily Capper, whose son John was among the dead, petitioned for the bodies to be recovered. In 1937, she sent the MP for Wrexham a petition carrying 2,158 names. Most of the men killed at Gresford remained in the mine.