Abstract: A method of and apparatus for use in establishing a blasting arrangement by loading at least one detonator (14) into each of a plurality of blast holes (30), placing explosive material in each blast hole, connecting to a trunk line (10) a control unit (32) that has a power source (52) incapable of firing the detonators, sequentially connecting the detonators, by means of respective branch lines (12), to the trunk line and leaving each detonator connected to the trunk line. In addition the apparatus includes means (46, 50) for receiving and storing in memory means (34, 44) identity data from each detonator, means (46, 50) for generating a signal to test the integrity of the detonator/trunk line connection and the functionality of the detonator, and means (46, 50) for assigning a predetermined time delay to each detonator to be stored in the memory means. The invention also extends to the control unit (32).