The invention relates to a blasting apparatus (10) for activating a plurality of electrical detonators (18) after predetermined time delays. The blasting apparatus includes a plurality of remote electrical delay devices (16.1...16.6). Each device is linked to a detonator (18), and is arranged to be serially programmed with a timing signal, which originates from a central control unit (12) and which determines the time delay. A bidirectional signal harness (14), having ends which terminate at I/O ports (20,22) in the control units (12), serially links the delay devices to the control unit (12). In the event of a fault (27) or discontinuity occurring in the harness prior (14) to programming of the delay devices (16.1...16.6), the discontinuity (27) is detected and the direction of programming along the bidirectional harness (14) is reversed so that those delay devices (16.4,16.5,16.6) which, due to the break (27), cannot be programmed in the initial direction (24), are programmed with timing signals travelling along the signal line in the opposite direction (26). The invention extends to a method of activating a plurality of electrical detonators (18), as well as to the individual delay devices (16.1...16.6) forming part of the blasting apparatus (10).