Underground » Environment - Subsidence and Mine Water
Informative and reliable dust monitoring plays an important role in identifying dust issues in underground coal mines and subsequently the development of effective mitigation strategies. NSW mining industry has a long record of dust sampling provided by Coal Services Pty Ltd. This testing programme has assisted the industry in achieving outstanding results in the elimination of black lung etc. Nevertheless, a number of limitations with the existing methodology have been identified, these include large number of failed samples due to contamination; provision of limited useful information that can be linked to specific activities and working environment, and thereafter cannot be used to assess and refine dust controls.
A critical review of the current dust sampling methodologies used in NSW and QLD in Australia as well as internationally has been conducted to identify their merits and limitations. The most common industry practice has been the used of gravimetric dust monitoring with cyclone separation and collection of the sized particles for weighing, generally over the period of a full shift to measure personal exposure levels to airborne contaminants of employees. The current testing regime in Australia provides the mine with a single figure for respirable dust exposure levels for 5 samples taken over a minimum of 4 hours during a production shift. These figures only provide information relating to the exposure levels of the person sampled, and does not provide any feedback on where the dust has come from or any other information that would allow the mine site to implement improvements in mitigation procedures should a non-compliance, or failure to statutory regulations occur.
A real time personal dust monitor (PDM) has been introduced into the Australian mining industry and extensive field dust monitoring work has been undertaken to evaluate the reliability and effectiveness of the instrument. The real time dust monitor can record dust loading on a continuous basis (a shift), or over a period of time, allowing mine operators to view their dust exposure levels during that period. The real time dust monitor has the ability to quickly identify high dust generation events such as during longwall chock movements and shearer cutting actions by recording higher spikes of dust levels in responding to these activities. As demonstrated in this study, the instrument has the potential to be used as an engineering tool to evaluate the effectiveness of dust control strategies. Up to date, the stringent regulations in Australian underground coal mines have limited the use of the real time PDM for routine dust monitoring, particularly in NSW.
The new dust monitoring method has proven to be reliable, robust, flexible and sensitive. Reliability has been proven by the parallel samples taken by Coal Services in which both results were very similar, the robustness is shown by the continued gathering of reliable and useful data, the flexibility is demonstrated by its ability to adapt to a required or designed testing methodology and its sensitivity is seen by the results identifying significant problems on longwalls, eg ventilation bypass, goaf over pressurisation, poor water pressure or flow to sprays, etc.
Dust measurements from this study indicate that operators struggle to remove greater than 30% of both respirable and inhalable dust produced on their operating longwalls. It is envisaged that a greater than 50% reduction in both respirable and inhalable dust can be achieved with best practice engineering, which will have a direct reduction in exposure levels to workers on the face and significantly reduce the risk of lung disease in employees.
Field trials of the new dust monitoring methodology have successfully identified the most efficient installed engineering controls operating at individual sources of respirable and inhalable dust generation on operating longwalls in Australia. By installing the best practice engineering controls, operators are in a better position to ensure compliance to regulatory standards for exposure levels and most importantly, they are ensuring minimum risk to worker health by ensuring they are mitigating the most respirable and inhalable dust possible from the mining environment.
Field demonstration of this new dust monitoring methodology has shown it to be a valuable and robust informational tool that will have a significant benefit to not only the underground coal industry, but all industry that are affected by airborne contaminants less than 10 micron in size. The ability to understand the actual dust production, coupled with the quantification of performance of installed engineering controls for dust mitigation, will give all operators of dust producing activities a valuable tool to better control their airborne contaminants. By better understanding and control of airborne contaminants, a significantly healthier workplace and environment will be achieved. This new dust monitoring system can therefore be used to:
· Measure and quantify dust loads at identified sources of dust generation utilising gravimetric sampling;
· Evaluate current dust controls and their effectiveness at each of the above sources of dust generation;
· Analyse the most effective control process in place for each source of dust generation; and
· Help the design of a monitoring process and best practices for implementation on to minimise dust exposure levels.
It is recommended that further studies be undertaken that include real time monitoring sampling in parallel to the DME model and identify if real time dust measurement data can quantify dust loads as well as exposure levels.