Engine Exhaust Emissions from Diesel Engines
Research by HSL to quantify the hazard arising from diesel exhaust emissions underground has continued this year. Diesel exhaust emissions from free steered vehicles (FSVs) have been monitored at Daw Mill colliery. The gases NO, NO2, CO and CO2 were monitored and samples of respirable diesel particulates were collected both on the vehicle and downwind. Earlier work at a salt mine had shown that CO2 offered a measure of air quality and that there was a very loose correlation between CO2 and the airborne diesel particulate concentration in terms of elemental carbon (EC). It was hoped that the same would be true in the coal mine so that an estimate of the EC diesel particulate concentration could be made. However, it was soon apparent that there were other sources of CO2 in the coal mine, and that background levels where there was no FSV activity were very variable and in excess of 2000 ppm. Consequently this approach was abandoned.
In line with the practice at the salt mine, all respirable particulate samples were scanned by a colorimeter to determine their 'blackness' prior to analysing for organic carbon and EC. In the salt mine it had been shown that, within limits, an estimate of the EC content of the sample could be made from measuring the 'blackness' of the sample. This was not thought to be possible in the coal mine because of the huge background EC from coal dust. However, the different characteristics of diesel particulate and coal dust gave very different curves in plots of 'blackness' against mass of EC on the filter. It was also found that, within limits, mixed coal dust/diesel particulate samples fell between the two curves and an estimate of the EC, and hence the concentrations of the diesel particulate from the samples collected at Daw Mill, could be made in the laboratory.
Although more work is required to establish the exact relationship between the colorimeter response and EC content, this method shows promise for the routine monitoring of diesel particulate in coal mines.
Improved dust sampling instruments for mines
The Health and Safety Executive (HSE) has commissioned a number of research projects to prepare for a review of the Coal Mines (Respirable Dust) Regulations 1975. HSL started work this year to identify instruments suited to both static and personal sampling of inhalable, thoracic and respirable dust in UK coal mines. This includes assessing instruments already developed and in regular use in the mining industries of other countries.
Work to date has included a review of available instruments for measuring dust and quartz in a mining context. The review analysed the dust measurement tasks that might be needed as part of a dust monitoring strategy. Instruments suited to screening measurements, comparisons with exposure limits, and detailed dust surveys were considered.
Some simple laboratory comparisons of respirable samplers with the current MRE 113A sampler were carried out. The work was limited to those instruments suitable for testing compliance with exposure limits. The best results were obtained using the French CIP10 sampler, which appears to be suitable for both fixed-point and personal sampling. Further laboratory and field tests of a wider range of instruments are now being planned.
Characteristics of airborne dust in coal mines
As part of the same review, the Institute of Occupational medicine (IOM) have been assessing dust concentration and exposures to ensure that the review of standards includes an assessment of what can reasonably be achieved in mines. The main review, reported on last year, was limited by a lack of up-to-date data on the size distribution and mineral composition of airborne dust in coal mines. A sampling exercise to fill these gaps was commissioned and IOM reported their findings this year.
With the co-operation of RJB Mining, TES Bretby collected 100 samples from 33 representative intakes, returns and headings at 9 collieries. Samples were collected by three types of personal samplers alongside the standard MRE 113A instrument. This allowed the measurement of concentrations of dust in various size fractions - respirable, thoracic and inhalable. The collected samples were then analysed for their mineral content at IOM's laboratory.
Concentrations of inhalable dust ranged from 2.3 mg/m3 to 57.7 mg/m3; generally two to three times greater, but up to 10 time greater, than the equivalent respirable dust concentration. This limited survey suggests the coal mining industry would find it very difficult to meet the current standard for inhalable dust which applies to surface industries.
There was little difference in the mineralogical contents of the dusts of different size fractions. Coal was the most abundant constituent but the total non-coal content, mainly clays, was usually greater than that of coal. The non-coal minerals would not generally have exceeded the occupational exposure standards for other industries.
IOM have also started work on two new projects to aid the evaluation of evidence on the health effects of coal mine dust. One aims to gain more knowledge of the exposure-response relationship between quartz and lung disease in order to illuminate the debate on an occupational exposure standard for quartz. The second aims to quantify the relationship between exposure to respirable coal mine dust and disabling lung damage other than the well-understood link to pneumoconiosis. Reports are expected in mid-1999.
RJB Mining has undertaken research work, both underground and on the surface, on the risks of Vibration White Finger and Whole Body Vibration. This has led to an introduction of risk control programmes within the company to identify potential hazards, monitor exposure, train the work force and where necessary modify work practices.