Blast confirmation

A blast system which includes a blast controller, a plurality of boreholes at a blast site, each borehole being charged with explosive material, a plurality of detonator assemblies respectively associated with said plurality of boreholes, each detonator assembly including a communication module, a detonator which in use is positioned inside a borehole exposed to the explosive therein, and conductors which connect the detonator to the communication module, wherein the communication module includes a control circuit which in response to receipt of a blast signal from the blast controller transmits a fire command signal at a time A via the conductors to the detonator thereby to cause initiation of the detonator at a time B, and a transmitter for transmitting a wireless signal, to the blast controller, which wireless signal contains or conveys an identifier which uniquely identifies the detonator assembly from which the wireless signal originated, said wireless being dependent, at least upon initiation of the detonator, wherein the transmission of said wireless signal from the detonator is selected from the following:

• (a) the transmission of the wireless signal commencing at the time B;
• (b) the wireless signal is transmitted at least for a period within which a measurement is made of a characteristic which is generated upon initiation of the detonator at the time B;
• (c) the wireless signal is transmitted continuously at or after the time A up to the time B;
• (d) the wireless signal is transmitted at the end of a time interval after the time B which interval is of sufficient duration to enable a measurement to be made of at least one event which is associated with initiation of the explosive, and wherein at least said wireless signals which are transmitted simultaneously by said transmitters from said plurality of detonator assemblies are modulated to promote multiplexing of the signals.