On the day of the accident, Wednesday 13 June 1917, it was business as usual at the works in Ashton-under-Lyne. Ironically, Lucien Gaisman was on his way back from a meeting in London to discuss the future of the company as an explosives manufacturer. A government report had recommended dispensing with smaller, less economic producers of explosives such as the Hooley Hill Rubber and Chemical Company.
Later that afternoon, Sylvain Dreyfus and a young chemist called Nathan Daniels were in the nitrating section of the works when the contents of number nine nitrator became unstable. Despite a frantic effort led by Dreyfus to bring the reaction under control, the contents of the vessel boiled over and set fire to the wooden staging around it. The fire quickly took hold, spreading to the roof of the building. The workers at the plant fought valiantly to bring the blaze under control, but it was all to no avail. Eventually the flames spread to a storage area where five tons of TNT packed into kegs was stored. A desperate call was made to the local police station for assistance at around 16.20pm and a few minutes later the works was torn apart by a colossal explosion. Most of the workers on site were killed instantly, including Dreyfus whose dismembered body was found in the factory yard. The factory building had been obliterated and two large craters scarred the site. The larger crater where the kegs of TNT had been stored, was approximately 90 ft by 36 ft across and 5 ft deep. The smaller, shallow crater was just below where the dryer and setting trays used for the final preparation of the TNT had been. Two gasometers in a nearby street were ripped open by the blast, sending a massive fireball hundreds of feet into the air. Hundreds of buildings in the surrounding area were damaged, leaving many of the nearby houses uninhabitable.
The casualties included forty-three people dead, over a hundred and twenty hospitalised and several hundred with minor injuries. Amongst the dead were twenty-three employees of the Hooley Hill Rubber and Chemical Works, along with eleven adults and nine children from the surrounding area.