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Safety and health in mines research advisory board

Annual Review 2004



Diesel Engine Exhaust Emission Monitoring in coal mines

Previously, a Personal Diesel Aerosol Sampler (PDAS) developed in the USA by the US Bureau of Mines and the University of Minnesota has been used by HSL to measure the exposure of workers to Diesel Engine Exhaust Emissions (DEEEs) at Daw Mill and Welbeck Collieries. The PDAS incorporates an impactor stage that performs a particle size separation at 0.8 micrometres. By arranging the cut at this point eliminates the larger coal dust particles, which would seriously interfere with the analytical method but collects the fine diesel particulate. This sampler has made it possible to measure the exposure of coal mine workers to DEEEs.

However, the PDAS used was not commercially available and the sampler and impactor substrates used were all made in-house to specifications supplied by the inventors. Unless a commercial version was made available then its potential was limited. More recently a USA company, SKC, has brought out a Diesel Particulate Matter (DPM) cassette, which is a once only use plastic cassette containing the impactor and filter assembly from the PDAS. This project was set up for HSL to determine if the SKC cassette offered a commercially available solution to monitoring exposure to DEEEs in UK coal mines. The objectives were:

  1. To use the SKC DPM cassette to determine the diesel particulate elemental carbon (EC) exposure of Free Steer Vehicle (FSV) drivers and key workers underground at Tower Colliery, and,
  2. Look at the potential of using a BOSCH smoke meter evaluator unit to measure the 'blackness' of SKC DPM cassette filter samples, as a simple and quick method to determine diesel particulate elemental carbon exposure levels in coal mines.

Using the SKC DPM cassettes, two FSVs were monitored underground at Tower Colliery and their Time Weighted Average (TWA) respirable particulate EC exposure concentrations were measured at 54 and 18 µg/m³. Compared to the HSE Technical Development Survey of exposure to DEEEs in surface industry this places the FSV drivers slightly above the mean for all the surface industry work groups but well below the highest exposed surface industry work group which was the fork lift truck drivers. The results were very much in line with FSV results obtained at Daw Mill and Welbeck collieries. Six fixed locations within the mine were also monitored and other than the FSV garage result of 34 µg/m³, all had EC exposures below 21 µg/m³.

Using a Bosch Smokemeter Evaluator Unit, the 'blackness' of the SKC samples was determined before each was analysed for EC. These data were combined with four SKC samples collected at Daw Mill and a linear relationship between Log EC and the Bosch 'blackness' number was determined with a correlation coefficient of 0.986. The conclusion is that the SKC Diesel Particulate Matter Cassette, when used in conjunction with the Bosch Smokemeter Evaluator Unit, does provide a simple on-site method for the determination of exposure to diesel particulate elemental carbon in coal mines.

Whole-Body Vibration

The Control of Vibration at Work Regulations, which come into force in July 2005, set action and limit values for occupational exposure to whole-body vibration. Only a limited amount of information is available on the whole-body vibration exposure of workers in the UK mining industry, however the data that did exist showed that daily vibration exposure can be above the limit value in the Regulations. The Whole-Body Vibration in Mining Industry Working Group set up by HSE is pursuing a programme of work aimed at establishing, and where possible, reducing the whole-body vibration exposure of workers in the industry.

HSL have carried out field trials at Fauld gypsum mine and Daw Mill coal mine to establish vibration exposure levels of drivers. These have shown that for scoop trams at Fauld and Free Steer Vehicles (FSVs) at Daw Mill the driver's exposure may exceed the limit value in the Regulations if they spend all, or a substantial part, of their shift driving. For other vehicles the daily exposures are between the action and limit values.

Although suspension seats were fitted to the vehicles tested most of the seats were found to be amplifying the seat base vibration, instead of providing the required attenuation. That is, the seats were increasing the vibration exposure of the driver. This was thought to be due to several factors: poor adjustment of the seat by the driver, poor maintenance, but principally the use of inappropriate seats for the vibration environment. Consequently the manufacturer of the seats was provided with the results of the field tests and asked if they could provide more suitable seats for the scoop trams and the FSVs. Following familiarisation visits to the mines, the manufacturer offered modified seats for testing in situ.

For the scoop tram a much heavier duty damper was provided for the existing seat. With this modification, and with careful set up of the seat, the daily vibration exposure of the driver was less than that found on the initial site visit, particularly when shock was considered. Therefore it is not proposed to carry out any further work at Fauld at present.

Based on the input vibration spectra supplied by HSL, the seat manufacturers offered a different seat suspension for the FSV. However in situ tests showed this alternative suspension system to be worse than the original seat. An examination of the input spectra from each set of measurements made at Daw Mill showed that the input vibration levels measured on the latter visit were significantly lower than those measured on the first visit. A different roadway was provided for the tests on the two occasions and this was thought to be the reason that the new seat was found to be inferior to the original seat. A minimum level of vibration is required to overcome friction in the suspension mechanism. This suggests that improving roadway conditions is the major factor in controlling whole body vibration and suspension seats have to be carefully matched to representative conditions if they are not to make exposure worse.

HSL also conducted WBV studies at Lochaline silica sand mine. The mine employs twelve people, three of whom use dump trucks to move sand from within the mine to a storage area on the surface. The floor of the workings is soft, wet and badly rutted. Two CAT 730 dump trucks have manually operated air suspension seats designed by Caterpillar in conjunction with Sears Inc (seat upper) and Milsco Inc (suspension). Objectives of the work were to investigate the vibration isolation performance of the driver's seats, and to determine the whole-body vibration exposure of the drivers.

The suspension seat fitted to the CAT 730 is designed to attenuate vibration in the vertical direction. However, neither seat reduced the vibration exposure of the driver. The seat in the first vehicle was found to be substantially amplifying the seat base vibration, while the seat on the second vehicle slightly amplified the seat base vibration. The vibration levels were found to be highest in the side-to-side direction. That is, rocking of the vehicle as it travelled over the deep ruts in the roadway was the most significant source of vibration. As the suspension seat fitted is designed to attenuate vibration in the vertical direction only, it was not reducing the vibration exposure of the driver.

The daily vibration exposure of both drivers was found to exceed the limit value for whole-body vibration given in the Physical Agents (Vibration) Directive that will be implemented in UK legislation in July 2005. In order to reduce the driver's vibration exposure it has been recommended that improvements be made to the roadway.

Upper Limb Musculoskeletal Risks

HSL carried out an ergonomic appraisal of the musculoskeletal risks to employees using a continuous miner control panel at Barrow gypsum mine, Loughborough. The task of operating the cutting control console involved a medium level of risk of musculoskeletal injury, under the conditions observed during a site visit where video footage and interviews were undertaken.

The key risk factors identified were:

Recommendations were made for reducing the risks:

Updated 2009-05-22