The NONEL UNIDET system is based on an inhole detonator with uniform delay times. All inhole detonators in the round have the same delay time and the firing sequence is built up on the surface with connection units with their own inbuilt delays. The delay time of the inhole detonators is normally chosen to be 500 ms which gives time enough for surface activation of all inhole detonators before any rock movement starts. Dyno Nobelâ€™s recommendation is to use 2 detonators in each charge when the hole depth is over 10 m or when the rock is fissured or water saturated. When the holes are fissured, it is common that the explosives string separates and then it is necessary to have one detonator in the bottom of the hole and another in the top part of the hole. The delay time of the bottom detonator should be shorter than that of the top detonator to avoid top initiation.