Underground » Health and Safety
This work is a continuation of other ACARP funded research conducted by the authors into diesel exhaust toxicity. The prior work firstly examined the change in diesel particulate matter (DPM) emissions produced by a number of alternative diesel fuels, finding a disparity between the 'amount' of DPM indicated by conventional mass measurements, and other metrics such as particle size and particle number. In subsequent work, an in-depth review was made of current research regarding the relationship between measurable DPM properties and the health risk to exposed workers. The importance of measuring the number of very small particles (< 50 nm diameter) was clear, but no reports could be found which assessed this aspect of the exhaust emitted from the water cooled systems seen on Australian underground vehicles.
This project commissioned a mine relevant diesel engine, complete with water-cooled wet-scrubbed exhaust conditioner, in a laboratory dynamometer test facility. Exhaust diesel particulate emissions were characterized in great detail, using the metrics which have been identified as most relevant to assessing health risk associated with DPM exposure: particle number, particle size, mass and organic compound concentrations.
Exhaust samples were taken from three locations within the exhaust conditioner, with the goal of learning the effect of the exhaust conditioner on toxic particulate formation. The conditioner was found not to affect the gross physical characteristics of the particles, but a portion of them seemed to be retained in the scrubber water. The organic carbon content of the exhaust was increased by the conditioner, but more work is required to ascertain the net change to health risk posed by this factor. Testing was limited to a single engine speed and load.
As anticipated, considerable difficulty was encountered in sampling the 'wet' exhaust from after the conditioner. The problems centred around water condensation within the dilution equipment and measuring instruments, and coagulation of exhaust soot within the sampling lines. These problems were partially solved, and the experience gained would enable further improvements to be made in future work, but the equipment used is not suitable for deployment underground without further development.
Three different dilution ratios were used when taking exhaust samples, representing the range of worker exposure conditions likely to be found underground. The particle physical characteristics were found not to be sensitive to the sampling dilution ratio. However, the concentration of organic compounds in the DPM was influenced by the sampling dilution ratio. This demonstrates the importance of matching sampling conditions with actual exposure conditions.
Several different instrument technologies were employed for the particle measurements. A comparison was made of the results obtained from each, across the range of dilution ratios and sampling locations used. The results indicate that reliable mass readings may not be obtained from filter collection methods at low dilution ratios, nor from laser light scattering instruments when sampling 'wet' exhaust. A portable instrument for measuring particle number and average size was found to give acceptable readings at high dilution ratios.