The cause of the disaster was not made clear at the time. There had been staff shortages, a management position had remained empty for a year and 194 inexperienced Italian POWs worked in the mines. In 1974, it was officially announced that the cause of the explosion was probably a site worker removing a detonator from a live bomb using a brass chisel rather than a wooden batten. An eye witness testified that he had seen a worker using brass chisels in defiance of the strict regulations in force.
Two huge explosions were witnessed at RAF No. 21 M.U. Bomb Storage dump on 27 November 1944 at 11.15 hours. Eye witnesses reported seeing two distinct columns of black smoke in the form of a mushroom cloud ascending several thousand feet, and saw a blaze at the foot of the column. According to the Commanding Officer of M.U. 21 (Group Captain Storer) an open dump of incendiary bombs caught fire and it was allowed to burn itself out without damage or casualties. Property was damaged within a radius of 3/4 miles of the crater.
Debris and damage occurred to all property within a circle extending for 1,420 yards (1,300 m). Upper Castle Hayes farm completely disappeared and Messrs. Peter Fordes Lime and Gypsum works to the north of the village and Purse cottages were completely demolished. The lime works was destroyed by the destruction of the reservoir dam and the subsequent release of water into the works. Hanbury Fields farm, Hare Holes farm and also Croft farm with adjacent cottages were all extensively damaged. Debris also damaged Hanbury village. The crater was some 900 by 700 feet (210 m) in length and 380 feet (120 m) deep covering 12 acres. Approximately one third of the RAF dump exploded, an area of 65000 square yards, but barriers of rock pillars between No. 3 and No. 4 sections held and prevented the other munition storage areas from exploding in a chain reaction. Damage from earth shock extended as far as Burton-upon-Trent.