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Safety and health in mines research advisory board

Annual Review 1999


Improved Dust Sampling Instruments for Mines

The Coal Mines (Respirable Dust) Regulations are currently under review by HSE. To assist that review, HSL is undertaking a project to identify instruments suited to both static and personal sampling of inhalable, thoracic and respirable dust in UK coal mines. The emphasis is on assessing existing instruments, i.e. those already developed and in regular use in the mining industries of other countries. As reported last year, a review of available instruments for measuring dust and quartz in a mining context 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.

This year field trials have been undertaken to assess the capabilities of dust sampling instruments to test monitoring strategies for a range of situations. Two types of monitoring strategies are being tested.

The first aims to identify those individuals whose work may give rise to significant dust exposure. Assessments have involved both personal sampling and fixed point sampling. Three different instruments - the HSL passive sampler, the NIOSH detector tube sampler and the CIP10 sampler have been used in the trials.

The second type of monitoring strategy that is being tested concerns the routine monitoring of a mineral-winning operation, intended to ensure that exposure is being adequately controlled below the exposure limit. These trials have been carried out over five days and involve both personal and fixed point sampling. CIP10 samplers and MRE samplers have been used in the trials.

The initial plan to visit six mines was increased to ten mines, in order to gather more dust exposure data in the small mine sector and to ensure coverage of different methods of working. The visits have included coal faces, headings, drivages and various types of small mine workings. In each mine visited, typically four fixed and four to six personal exposures have been measured each day, with the visits covering a total of six working days. TES Bretby Ltd have worked alongside HSL to measure fixed point dust concentrations using the MRE dust sampler. An occupational hygienist from the Institute of Occupational Medicine (IOM) has accompanied HSL staff on one day in each mine, in order to gather occupational hygiene data.

Analysis of the dust sampling data is ongoing. However early results show excellent performance from the CIP10 sampler, which shows a high degree of correlation with the MRE sampler when the two instruments are used side by side. As expected, personal exposures are much more variable than fixed point measurements. The personal measurements are taken over the full shift whereas the fixed point measurements are at the working place only. The NIOSH detector tube sampler is also showing promise as a low-cost, direct-reading dust instrument.

Occupational hygiene Assessment of Dust in Coal Mines

During 1999, IOM occupational hygienists visited the mines where personal exposure measurements have been made and advised on the recording of relevant information by HSL scientists. Close consultation with HSL will ensure that IOM fully understand the context in which their measurements have been made. IOM hygienists have also collected information about working practice underground, attitudes to sampling and changes in the industry to update that collected in an earlier review. The report is expected in 2000.

Dust-Related Risks of Clinically Relevant Lung Functional Deficits

HSE commissioned IOM to carry out a project involving further analysis of data for 7000 coalminers who were working at nine collieries in the late 1970s, gathered as part of the long term Pneumoconiosis Field Research programme. Three questions were posed:

  1. What deficits of forced expired volume in one second (FEV1) influence detectably the level of exertional breathlessness in miners?
  2. What definitions of clinically relevant deficits of FEV1 does this suggest?
  3. What are the quantitative relationships between cumulative exposure to respirable coalmine dust, and risks of these clinically relevant deficits, overall, and specifically over the range of low exposures likely to be encountered in modern British mines?

FEV1 is an objective measure of lung function which may be reduced in a range of respiratory conditions including both pneumoconiosis and chronic bronchitis/emphysema (chronic airflow limitation). Definition of what constitutes a clinically important degree of functional impairment is relevant to the assessment of risk in a regulatory context. The aims of this study were, therefore, firstly to relate the objective measure of lung function to subjective reports of breathlessness in order to identify clinically relevant deficits of FEV1 and, secondly, to define the levels of exposure to coalmine dust which would give rise to these clinically relevant deficits of FEV1.

The study has been completed and the final report (TM/99/06) published by IOM. There was no clear level of FEV1 which enabled separation of individuals who were breathless from those who were not. Overall, however, levels of FEV1 were lower in those reporting breathlessness. It was only possible, therefore, to define the probability of reporting breathlessness at any given FEV1 (age and smoking) level.

Cumulative exposure to dust was examined in relation to a 'doubling of the risk' of having a clinically relevant deficit of FEV1, that is doubling the odds of reporting breathlessness. There was a significant association between dust exposure and level of FEV1 with no evidence of a threshold. An increase in cumulative dust exposure of 50ghm-3 was associated with an increase in the order of 1 to 2% of men with clinically relevant deficits.

At a cumulative dust exposure of 120ghm-3 (an average 2mgm-3 over 35 years) approximately 30% of 60-year old non-smokers would be expected to have a 'doubling of risk' compared to around 25% of 60-year old non-smokers not exposed to dust. Reducing the average dust exposure to 1mgm-3 the corresponding percentage would be about 27.5% thereby giving a reduction of 2.5% compared to that for an average concentration of 2mgm-3.

The IOM conclude that reduction in the workplace standards for respirable coalmine dust would result in a small but significant decrease in the percentage of workers whose lung function was reduced to a level associated with a doubling of the odds of reporting symptoms of breathlessness.

Exposure to Respirable quartz and Silicosis Risks

HSE has also commissioned IOM to carry out this project, also involving further analysis of the Pneumoconiosis Field Research survey data. The objectives are :

  1. To gain a more detailed knowledge of the shape of the exposure-response relationship between the patterns of accumulation of quartz exposures and the risk of developing pneumoconiotic abnormalities.
  2. To investigate the extent to which knowledge of that shape is improved by using dose measures other than simple cumulative exposure, or models other than the simple linear logistic.
  3. Using the best available model, to produce predictions of risk under various scenarios of exposure which will illuminate the debate on what level is appropriate for an occupational quartz standard.

During 1999, the work has focused on production of the appropriate data sets, description of the exposure characteristics of the study sample and on exposure-response regression modelling. Exposure time profiles have been constructed and compared between those with and without signs of radiographic abnormalities at follow up. These suggest that the period principally associated with radiographic abnormalities was the first half of the 1970's when quartz exposures were known to have been unusually high.

Initial regression modelling, using a general exposure index, has indicated that simple cumulative exposure may not be the most appropriate 'measurement' for discriminating between those with and without later radiographic abnormalities. The work continues. A report is expected in 2000.

Physiological Monitoring of Heat Stress in Mines

RJB Mining (UK) Ltd. is the major sponsor, with HSE also contributing, of this project in which IOM aims to validate the measures proposed in the IOM Code of Practice for Work in Hot and Humid Conditions in Coal Mines. The project aims to determine the level and pattern of workload from measurements of heart rate associated with differing mining tasks and to determine the levels of physiological heat load from measurements of body temperature associated with working in hot temperatures underground. The collected data will be used to examine current predicted levels of heat stress to determine the appropriate criteria for the introduction of control measures in order to validate those proposed in the IOM Code of Practice. Data has been collected from two collieries and was being collected from a third at the year end. The data collected relates to Body Core Temperature (via the aural canal) and heart rate measurements. It is anticipated that the final number of data shifts will be in the region of 200.

Following the third hot mine visit it is intended to visit a cool mine where data can be collected to form a comparison between heart rates in a cooler mine to those of a hot mine carrying out similar activities. A report is expected in mid 2000.

Use of Diesel Engines Underground

A project was undertaken at HSL this year to investigate the effect of introducing biodiesel fuel on the quantity of exhaust-emitted particulates, gases and vapours. Comparative studies have been made over a standard eight-mode test cycle on the exhaust emissions from a fully flameproofed mining diesel engine fuelled on:

Overall the results show that, for equivalent engine conditions, the exhaust emissions from biodiesel fuel contain less particulates, gases, aldehydes, and polyaromatic hydrocarbons (PAHs) than the exhaust emissions from Class A1 fuel. There was no instance where the biodiesel exhaust emissions were worse that the Class A1 diesel fuel. The 30% blend exhaust emissions were not as low as the biodiesel fuel but were significantly lower than the Class A1 fuel. Summing over all engine conditions, the respirable particulate emission rate was reduced by 58% with biodiesel and 42% with the blend when compared to Class A1 fuel.

Performance of Respirator Fitters against Diesel Fume

Work was carried out this year at HSL to examine the efficiency of respirator filters against diesel fume. The following were selected for test:

Samples for test were cut from the above and mounted on a laboratory apparatus. This apparatus allowed filter materials to be simultaneously exposed to a test aerosol in such a way that the fraction of test aerosol penetrating through each could be measured under identical conditions of exposure. The test aerosol was diesel fume generated by a caterpillar 334 PCNA engine, 7 litre capacity, operated at maximum power and torque, fuelled with A1 diesel fuel. The performance of the filters was continuously assessed for a period of seven hours, by the end of which large deposits of fume on the samples were observed. It was found that none of the filters tested suffered a significant increase in aerosol penetration as a result of loading, and the initial performance could therefore be used to estimate the protection offered by the filter materials in practice. The disposable mask currently used in coal mines in the UK allowed no more than 7% of the diesel fume to penetrate. A second mask with comparable resistance to breathing performed in a similar way. Other, higher resistance, masks allowed less than 0.1% of the fume to penetrate. Face seal leakage limits the real protection offered by masks of this sort, and it can be concluded that the mask used at present offers a level of protection as high as could reasonably be expected with RPE of this type.

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Updated 2012-01-20