Abstract: A sequential blasting system includes a plurality of electrically fired detonators and a pyrotechnical activated switch associated with each detonator. On firing of a detonator, the associate pyrotechnical activated switch primes the sequentially next to be fired detonator. Alternate detonators are connected to first and second conductors, respectively, through an alternating sequencer, which sequencer alternatingly connects the first and second conductors with a source of electrical power to fire the detonator primed by the previously actuated pyrotechnical activated switch.