Bulga Coal blasts between 9am and 5pm, Monday to Saturday, with the majority of blasts fired around lunchtime. Blasting is managed in accordance with the approved Blast and Vibration Management Plan and complies with the conditions outlined in the Environmental Protection Licence 563 and in our development consent.
Before mining can begin, topsoil is removed and stockpiled so that it can be reused during the rehabilitation process. Once the topsoil has been removed, it is necessary to blast the underlying rock so it is broken into a manageable size which can be handled by either the dragline or excavators.
Blast management aims to minimise the impact to the community through blasting activities. Noise, overpressure, vibration and dust exposure from blasting activities must comply with limits that are set by regulatory authorities for neighbouring residential properties.
Monitoring is undertaken to record:
- Measured air blast overpressure;
- Measured ground vibration; and
Results from the blast monitoring are reported quarterly on the website in the Environmental Monitoring Report and also reported in the Annual Environmental Management Report.
Bulga Coal is continuing to improve our blast performance to reduce the incidence of fume generation.
In 2010, the Bulga Complex undertook an investigation into blast and blast fume. The main components of blast fume are Nitrogen dioxide (NO2) and Nitric oxide (NO). In concentrations of more than 30ppm, NO2 is indicated by the red-brownish colour of blast fume.
Blast fume cloud is created by an incomplete explosion and factors such as:
- Presence of moisture in the ground;
- Atmospheric conditions including wind speed, directions and temperature inversion;
- Blast design parameters, including size of the blast and stemming;
- Geology; and
- Quality of the blasting product.
Fume concentrations were monitored with two ODALOG 6,000 gas monitors per blast. The gas monitors were positioned at different distances downwind of the blast within the 500 metre clearance zone.
The analysis of the collected data from the 15 blasts indicated that none of the workforce or community were exposed to fume gas levels above the occupational exposure levels or Office of Environment and Heritage criteria. Recent trials of a high grade blast product showed it can reduce the potential generation of an orange fume cloud. This product is now being used at Bulga Coal in difficult blasting conditions.
Bulga Coal will continue to collect data with the assistance of air quality experts to enable the atmospheric modelling of the monitored blast including the concentrations of fume constituents. A health assessment of the predicted fume concentration the workforce and public may be exposed to will then be undertaken and the results will be made public.