Abstract: This invention provides a method and apparatus for electrically, sequentially activating a sequence of initiators, to sequentially initiate a series of explosions, such as in blasting or with propellants. The invention provides a series of activating modules that each has a switch which is disabled by the preceding activating module until the initiator of the said preceding module has been activated. The activating modules are further arranged in sets so as to be selectively energized from a suitable power supply. In a preferred form the switches are uni-directional and the activating modules are connected between a pair of supply cables with the switches of alternate modules being of opposite polarity. The activating modules are then selectively energized by reversing the polarity of the power supply. In an alternative form the activating modules are connected to have a common power return cable with the activating modules of each set being connected to individual power drive cables.