8.1. BLAST PERIMETER
The person responsible for the firing of the shot is the person who has to determine the exclusion zone and the location or distance from the shot of the guards. This should be determined from a risk assessment taking into consideration technical concerns or known hazards in the shot.
8.2. WARNING PROCEDURES
8.2.1. External Parties
It may necessary to pre-notify certain external parties before conducting blasts. This may be adjoining mines, residences or such things as warning air traffic controllers against low flying aircraft movements.
8.2.2. Withdraw of Personnel
Persons in the vicinity of the blasting area need to be warned and withdrawn to a safe area outside the exclusion zone before firing the shot. They should not return until the ‘all clear’ signal is given (AS 2187.2). Each person involved in firing the blast has to be able to reach a predetermined safe position, by walking at normal pace, before the blasting happens.
8.2.3. Audible Warning device
An audible warning device can be used to indicate that a blast is going to take place. The device should produce a sound that is clearly identifiable from any other sound, which might be used for warning or operational signals on the site (AS 2187.2). Signs should be provided indicating the audible warning device is a signal that blasting is taking place.
8.2.4. Radio Signal
Where a radio is used to give an audible signal all personnel onsite should clearly understand the implication of the signal. Whilst the signal is audible all personnel should maintain radio silence, except for extraordinary circumstances. Where there is more than one radio channel used on a site, best practice is to select a blasting radio channel that is always used for this purpose. Where there are likely to be users of other channel in the blast locality, then the firing warning should be broadcast simultaneously on all those channels.
8.2.5. Access Guards
Adequate roadblocks or warning signs or, where necessary guards shall be placed along drives to prevent unauthorised machinery or people entering the blast area or exclusion zone (AS 2187.2). All means of entry to the blasting area need to have guards to prevent unauthorised access or effective barricades erected across each place of entry.
Figure 13: Access guard with signage
8.2.5.1. Competency of Guard
The blast guard is required to understand where their expected location is and the sequence of events that will take place while the shot is being fired. They should park their vehicle at approx. 90 degrees to prevent the flow of traffic and have suitable markings. If someone does drive past the blast area they shall notify the person in charge of the blast i.e. the shotfirer, immediately.
8.2.5.2. Guard Location Sheet
Where there are numerous guards required, best practice is for a guard location and radio procedure record to be kept by the shotfirer. This document can include the blast guards’ names and responsibilities. A pre-firing security check is then to be undertaken by the shot firer using the radio and a map of the blast area to confirm the guard’s locations. This record alleviates the possibility of a blast guard not being involved in the final check by the shot firer prior to firing.
8.3. BLASTPED FIRING
The BlastPED EXEL System allows remote, centralised blasting using a radio based link between the shot firer and blast site. Where a BlastPED is used for remote firing the user needs to ensure that the remote receiver is on and the signal tube connected to the 'sparker' only immediately prior to firing. Once the area has been cleared of personnel and permission to fire received, the master control operator can turn the controller on (from a remote and safe location), enter their PIN, and check the status of the receiver via the encoded radio link between the units. The ‘arm and blast’ commands can then be transmitted.
Figure 14: Master Control Unit used in BlastPED Excel remote firing
8.4. BLAST MONITORING
Where blasting is conducted in close proximity to buildings or structures, ground vibration and airblast overpressure needs to be monitored to record the blast characteristics and in the longer term provide help to ensure that the probability of damage or human discomfort is kept to a minimum. Where protection from fly is
necessary, precautions such as the use of blasting mats or other suitable cover and limiting the explosive weight per delay can be used.