1 when the flame reaches the bottom of the delay column 4 c it fires the explosive charge 10 contained in striker piston 5 this explosion generates a large amount of gas which remains confined in cavity 8 because the delay column has been plugged by the solid slag 4 d the purpose of this reaction is to shear off the collar and force the striker piston downward the latter can then strike detonator 11 however to reinforce the safety of these means when the striker piston 5 is released accidentally despite a correctly loaded delay composition the means according to a preferred embodiment of the invention are disposed such that the explosive charge 10 is located in a cavity 6 inside striker piston 5 these accidental starts may occur for many reasons influencing the delay composition 4 or the explosive charge 10 both being deemed to be highly sensitive they include extreme environmental conditions such as high temperatures or accidental conditions occurring during storage transportation or handling before such means are implemented it should be noted that other factors may intervene in the accidental release of the piston such as being struck by a bullet or the primary explosive detonating because of an outside explosion despite the fact that the detonator 11 is misaligned from the striker piston 5 there is always a risk of propagation.