Physiological Monitoring of Heat Stress in Mines
The Institute of Occupational Medicine (IOM) has completed a project, sponsored by RJB Mining (UK) Ltd. and the HSE, aimed at validating the measures proposed in the IOM Code of Practice for Work in Hot and Humid Conditions in Coal Mines. Data was collected at three hot and humid mines and one cooler mine, including Body Core Temperature (via the aural canal) and heart rate measurements of miners at work. The report, published by IOM as TM/00/05 in November 2000, presented nine conclusions:
Assessment of Exposure to Vibration in Mines
HSL has carried out a series of studies of exposure of miners to hand arm vibration for HSE's mines inspectorate. Measurements have been made at a bathstone mine, a coal mine and an ironstone mine to assess vibration exposure from the use of powered hand tools, to compare the results with any from the mining companies' own monitoring systems and to assess some low-vibration alternative tools. They will also allow an assessment of the likely impact on the mining sector of any future regulations derived from an anticipated European Directive.
During the study, hand-arm vibration exposure measurements have been made on jigger-picks, roof-bolters, side-bolters and rock drills. The results indicate that impactive tools such as jigger picks and breakers can generate high levels of vibration, restricting recommended usage times to as little as 10 minutes. Tools with vibration reduction features showed varying degrees of reduction (up to 50%), but still need usage times restricted to as little as 30 minutes. The low vibration versions were often reported to be inefficient so a given task required a longer usage time. Roof-bolters were found to generate vibrations below 2.8m/s² and are, therefore, unlikely to cause exposures above HSE's recommended action level.
A small investigation has also been carried out into the long-term effectiveness of anti-vibration gloves. This study showed that after a short period of use in a bathstone mine the resilient material used in the anti-vibration glove tested became permanently compressed, resulting in negligible vibration reduction.
Further measurements of vibration in UK mines are planned for 2001, including a small survey of whole-body vibration exposures. The aim is collate the information in terms of the action levels and limit values proposed for the European Directive.
Improved Dust Sampling Instruments for Mines
After investigating the range of available instruments for dust sampling, as reported last year, the CIP10 sampler was identified as the best choice overall for routine, accurate measurement of respirable coal mine dust. Field trials were carried out in ten coal mines in order to assess the instruments and dust monitoring strategies. The trial sites included coal faces, headings, drivages and various types of small mine workings. The results from all visits were analysed and written up as a comprehensive report during May 2000.
Since then, an investigation was carried out into the accidental switching off of the CIP10 sampler in the vicinity of conveyor magnets. This showed that the problem was likely to occur very rarely and no special modifications to the instrument were warranted.
The coal mine survey highlighted the need for a validated method for the analysis of the quartz content of CIP10 dust samples. A collaborative study was carried out between HSL and TES, to develop an analytical procedure and validate its results against those obtained using the MRE 113A sampler.
The project ended in December 2000. The main findings from the project were that the CIP10 personal dust sampler has potential for use in UK coal mines, as an alternative to the MRE 113A sampler. The CIP10 instrument can be used both for personal and static monitoring, and the results obtained with it, when used as a static sampler, are highly correlated with the MRE 113A results. Methods for determining both respirable dust and quartz concentrations with the CIP10 have been developed.
The work carried out during this project has been presented at a number of meetings of the Deep Mined Coal Industry Advisory Committee's working group which is considering possible new regulations on inhalable dust, and to a meeting of the Institution of Mining and Metallurgy. Further presentations are planned at two conferences in 2001. The work was also written up for publication and is in press with the Transactions of the IM&M.
A follow-on project started in January 2001 with the aim of giving the British mining industry more experience of sampling with the CIP10 and HSE more data on which to propose limit values for the new regulations. All the operators of major mechanised coal mines, four operators of small mines and three laboratories are collaborating in the project.
Relationship Between Exposure to Respirable Quartz and Risk of Silicosis.
The Institute of Occupational Medicine (IOM), Edinburgh, has recently completed a project for HSE's Health Directorate aimed at gaining a better knowledge of the relationship between the patterns of exposure to respirable quartz and the risk of developing silicosis. The study re-examined data collected during the Pneumoconiosis Field Research (PFR) programme at one Scottish colliery where adverse geological conditions in the last decade before its closure in 1981 meant that sandstone roof and floor was machine cut along with the coal seam. The miners were exposed to higher quartz exposures and subsequently showed more rapid progression of silicotic abnormalities on their chest X-rays than was typical of the others participating in the PFR programme.
This study looked at a group of 547 surviving men who had routine X-rays in the 1970s and also attended for follow-up in 1990/1. Men with ILO category 2 chest X-rays at follow-up had spent, on average, 38% of their working time in quartz concentrations above 0.1 mg/m3, 4% of which was at more than 1.0 mg/m3. For 18% of their working time, quartz made up 10% or more of the respirable dust they were exposed to.
Statistical analysis showed that the risk of contracting silicosis was more closely related to the sum of the times spent in occupational groupings weighted by the square of quartz concentration than the usually accepted model where risks from coal mine dust are simply related to cumulative exposure. This model would predict that only twelve months exposure to 2 mg/m3 quartz was associated with a 73% risk of category 2/1 or greater silicosis. For lower concentrations, however, conventional cumulative exposures did appear to describe risks adequately. The lowest exposure associated with category 2/1 or greater silicosis was equivalent to average concentration over 12.25 years of 0.1 mg/m3 and the model would predict a 1.7% risk at a quartz concentration of 0.1 mg/m3 over a period of 10 years. This risk would, however, be doubled by an additional two month exposure at a concentration of 2 mg/m3.
The report notes other research which suggests coal and other minerals may ameliorate the biological effects of quartz when it is present in small proportions. Indeed, the overall conclusion drawn from the PFR is that quartz is a relatively unimportant determinant of risk from coal mine dust. Conditions at this particular mine clearly exceeded the threshold for any protective effect of coal against the effects of quartz.
The results demonstrate the potentially high risks associated with even brief exposures to high quartz concentrations. Where high or fluctuating levels may occur, frequent monitoring of concentrations is advocated, along with prompt intervention and appropriate measures aimed at controlling peaks as well as minimising average exposures.
The report has been published by IOM as TM/01/03.
Use of Diesel Engines Underground
In a previous phase of this project, HSL proposed a method for estimating the composition of mixed diesel particulate and coal dust samples, based on measuring their 'blackness' and elemental carbon (EC) content. Further work has been carried out in the laboratory to try to improve the method and to obtain a mathematical solution for estimating the composition of mixed samples. During these studies, it became apparent that the size distribution of the respirable sample collected affected the relationship between 'blackness' and EC. As the size distribution of coal dust varies from one location to another it is therefore not possible to draw a single calibration curve which will satisfy all situations. At this point it was evident that this method was not going to satisfy the need for means of measuring diesel particulate in coal mines.
After discussion, a new approach was tried using samplers developed in the USA for measuring diesel particulate in the presence of coal dust. These samplers use three consecutive stages to separate and collect respirable mineral and diesel particulate from sampled air. The first stage acts as a respirable preclassifier; the second stage as a 0.8 µm impactor that collects aerosol greater than 0.8 µm in size; the third stage as a filter that collects aerosol less than 0.8 µm in size. Evidence shows that virtually all diesel particulate is less than 0.8 µm and almost all coal dust is greater than 0.8 µm. Previous work carried out by British Coal Laboratories on prototypes of these samplers showed that the samplers have limitations and that, in some cases, the diesel particulate fraction could consist of up to 30% coal dust. However, it was believed that with better methods of analysis, this method could offer a solution.
The impactor stage of these samplers is not commercially available but NIOSH, USA loaned ten impactors and provided instructions for producing the substrates which trap the coal dust. A rigorous procedure for producing the substrates was devised at HSL.
Ten working samplers were assembled and laboratory trials carried out to compare their performance against standard respirable cyclone samplers and to determine their efficiency in trapping coal dust.
Using these samplers, diesel particulate samples were collected at Daw Mill Colliery. Samples from both fixed locations in main roadways and on free steer vehicles (FSVs) were obtained. These samples were analysed in the laboratory and a method for estimating the mass of coal dust present on each filter developed. A full report is expected early in 2001.
IMC-TS completed work on a project related to the control and prevention of noise in mining operations and the final report has been submitted to ECSC. The work addressed the potential for reducing noise emissions from shearer drums, pneumatic bolting equipment and auxiliary fans through modification of design. The mainly desktop study indicated that significant reductions in noise emissions were achievable. In a further topic area, a large amount of underground data was gathered in relation to noise attenuation along underground roadways, in drivages and at junctions for use in conjunction with an existing noise prediction software package.