The main explosives risks associated with the drilling of blastholes are residual explosives from previous blast being initiated and poorly drilled holes creating an unsafe situation during firing. Blast geometry and design is imperative to create safe discharges and blast results required for mine operating parameters. Blasthole diameter, angle and length are required be adequately designed for the selected drill pattern. Correct drilling of blast designs will ensure that safety hazards such as overbreak, fly or airblast overpressure are significantly reduced. The following standards and procedures should be in place to ensure holes are drilled safely and
create a safe discharge:
- The drilling site is prepared and drill holes marked out prior to drilling.
- Drilling is not carried out on any face or bench until it has been examined for misfires and suitably treated (refer to Section 9 of this Guidance Note for the treatment of misfires).
- The driller is provided with a drill design that specifying hole and collar lengths, direction and any expected geotechnical conditions.
- The driller records any unusual events during the drilling, for example cavities, soft rock, or an inability to drill designated holes.
- When positioning the drill rig along the edge of the bench the drill rig should be positioned so that the operator has a clear view of the edge at all times and is protected from falling.
- Whilst drilling near the bench edge the drill rig should be orientated so as to reduce the risk of the drill rig toppling.
- Drilling is not carried out in a hole where any part of it is considered within an unacceptable distance from a hole containing explosives.
Note:
If it is essential to drill in, or relatively close to, an old hole or butt, it should be carried out only with remote-controlled drilling equipment (AS 2187.2). The operator and all personnel need to be withdrawn a safe distance from the old hole or butt.