In a pyrotechnic plant, an explosion detonated during fireworks production when exposed to compression. The technician was manufacturing 27-mm calibre violet stars through the use of a pyrotechnic composition based on potassium perchlorate, sulphur, copper oxychloride and dye. The quantity involved was approx. 3 kg. This production operation consisted of compressing the composition by means of a punch and rubber mallet within a bronze mould composed of 10 cylinders. The deflagration occurred as the material was settling in one of the cylinders. A blast was felt along with the projection of metal pieces stemming from the mould. The technician was injured on the thigh by shattered debris. Property damage was limited; only the machinery was destroyed. This incident was caused by the percussion of the punch on the bronze prong lying at the bottom of the matrix. The operator installed a protective screen in front of the workstation between the mould and the remaining composition, in addition to completing technician protection with a copper apron and modifying the machinery layout (elimination of 4 cylinders on the mould, increase in cylinder height, creation of a thrust bearing to avoid all contact between the punch and the prong).