4.8.4. When it is found that a defect in the electrical circuit has prevented the charges from detonating at time of firing, the shot-firer may immediately check over the circuit after having made sure that:(a) the ends of the lead wires are disconnected from the power supply and short-circuited;
(b) the blasting machine is locked or under a worker’s surveillance; and
(c) if used, the blasting switch is locked and in open circuit.