Open Cut » Environment
Large quantities of ammonium nitrate fuel oil (ANFO) explosive are used throughout the open-cut coal mining industry in Australia each year. Individual mines can consume more than 50,000 t of ANFO and related products annually. Apart from dust generated by blasting, under ideal conditions the only gaseous products from ANFO explosives are CO2, nitrogen and water. However, in some cases certain toxic gases including nitrogen dioxide (NO2) may also be formed. It is NO2 that causes the distinctive orange-red coloured 'fume' that sometimes accompanies blasting. These gaseous blast products may be carried considerable distances across the mine or even beyond the mine boundary. Given the proximity of some large mines to populated areas and the potential for worker exposure to toxic gases, there has been concern about the impact of blasting fumes.
The primary aim of this study, ACARP Project C18034, was to monitor NO2 concentrations in the ambient air near the fence line of a large open-cut coal mine in the Hunter Valley. Monitoring was undertaken using ultraviolet differential absorption optical spectroscopy (DOAS), which is an open-path method where NO2 was measured in a light beam about 250 m long. Two monitoring sites were selected at the mine so that the prevailing winds would be expected to carry blast plumes over the monitoring sites.
Measurements were made using the DOAS systems from April 2011 until October 2012. Monitoring at a third site adjacent to a mine administration building and carpark were also made over a four-month period between November 2010 and April 2011 using a chemiluminescence NOx analyser.
As well as NO2 monitoring, periodic sampling was undertaken in the pit to identify hydrocarbons emitted during blasting.
The key findings of this project are detailed in the report.
It is clear from the measurements made during this project that there are other significant sources of NO2 apart from blasting. These include emissions from diesel powered equipment operating at the mine and sources beyond the mine boundary such as power stations, vehicle traffic and railway operations. It is therefore suggested that detailed regional air quality modelling be undertaken to better define the ambient NO2 (and other species) levels likely to be encountered across the mine site throughout the year. This would allow ambient levels of a range of pollutant species present on mine sites to be attributed to their actual sources. The contribution of emissions produced from blasting (and other mining activities) could then be reliably compared to those from other non-mining related emission sources.
An important prerequisite of reliable modelling is an accurate inventory of emission sources. While some of these are known to within reasonable limits (such as power stations), others are much more uncertain. In particular, estimates of emissions from blasting currently rely on the use of emission factors which are subject to high levels of uncertainty. More detailed research targeted at measuring emissions from individual blasts would significantly improve the current understanding of the true extent of emissions of NO2 and other compounds within the open-cut coal industry.