WHOLE BODY VIBRATION IN MINING
HSL completed a short investigation for the Mines Inspectorate into whole-body vibration (WBV) exposure from free steered vehicles in mines. The measured exposure values were compared with the action and exposure limit values used in the proposed EU Physical Agents (Vibration) Directive. This allows member states to decide whether to express exposure in their national legislation in terms of root mean square averaging over an 8 hour day or as a vibration dose value (VDV). VDV uses the fourth power averaging of the instantaneous acceleration and is more sensitive to vibration shocks, which are believed to be important in the development of lower back injury.
The work showed that many mine vehicles produced whole-body vibration exposures higher than the proposed action level. While no vehicles exceeded the 8 hour daily exposure limit value based on r.m.s averaging of vibration, many exceeded the VDV exposure limit value.
As a follow-up, an assessment of foam pads for control of WBV in mine vehicles has commenced. This work is looking at the potential of combinations of foam materials to provide improved comfort and reduced vibration exposure where height restrictions limit the options for other seat design solutions.
Removing HAND-ARM vibration risk
Hand-Arm Vibration problems associated with hand held pneumatic machines used for installing both cable bolts and rib bolts is becoming an increasing problem despite manufacturers’ claims of reduced exposure levels. There is a need for systems and machinery which can remove this risk completely. UK Coal has organised a project team with representatives from machine suppliers and guidance from the HSE to develop machinery to comply with this requirement. The first prototype machine will initially be trialled for cable bolting at Harworth and Rossington mines and is due to start early in 2002. The next generation machines will be designed and developed for systematically rock bolting at the face of a development heading. These machines are currently in their development phase with an expected under ground trial planned at Clipstone Colliery later in 2002.
Personal Sampling of dust in coal mines
Last year’s review reported on a project which found that the CIP10 personal dust sampler had potential for use in UK coal mines, as an alternative to the MRE 113A sampler for static sampling and also as a personal sampler. This project, which started in January 2001, was conceived by the Deep Mined Coal Industry Advisory Committee’s working group considering possible new regulations on inhalable dust. It aimed to give 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.
The CIP10 was widely accepted by the mineworkers involved in the field trials but there appeared to be problems at some locations where improbably high dust loadings were observed. Size analysis of the sampled dust showed that particles beyond the respirable range were reaching the sampling foam. Further laboratory trials found that the flowrate through the CIP10 is dependent upon the speed and direction of the wind and on the dust loading on the size selective foams. In addition, it was found that large particles, collected in the size selective foams, can become dislodged and move to the respirable foam when exposed to vibration similar to that from man-riding belts.
This meant that the conditions found underground in some British coal mines were beyond the range where the CIP10 could be used with confidence in its ability to maintain the correct flowrate, and therefore to select the respirable fraction of the airborne dust in coal mines. In addition, under certain circumstances the integrity of the respirable sample is compromised. The decision was made therefore to stop work with the CIP10 and to explore the use of alternative personal samplers.
Laboratory tests have been carried out with a small personal cyclone developed in the 1970s by SMRE for use in coal mines and known as the SIMPEDS. The proposed new system combines a lightweight, plastic version of the cyclone with a small personal sampling pump and mounts them on a suitable lightweight harness that is currently used underground. The tests were designed to highlight any potential problems with the use of the system in the arduous conditions found in coal mines before restarting the field programme. The results obtained so far have shown that the cyclone sampler does not suffer from the particle movement problems experienced by the CIP10 under simulated man-riding vibration. Tests with various cassettes for use with the cyclone have shown that a metal cassette is essential for reliable gravimetric analysis. A lightweight sampling pump, used in the US coal mining industry, has been tested and found to be excellent for this role. Tests to determine whether the performance of the cyclone is affected by the high wind speeds experienced on the coal face close to the shearer were due to be carried out early in 2002. If successful, the programme of wearer trials at mines would restart.
This HSL project aims to develop new, rapid methods to evaluate problems involving airborne dust, including issues such as dust sampling, dust inhalation and dust control. An innovative approach is being investigated that allows the experimental work to be carried out using small-scale models of the full-scale situation. This is a seven-partner EU-funded project with partial support from HSE’s Mines and Factories Inspectorates.
Work during 2001 has concentrated on investigating the magnitude of the losses of particles to the internal walls of the piping connecting the sampler inlet to the particle monitor. This piping is normally copper or stainless tube of internal diameter 15 to 20 mm and includes a horizontal section, a 90°bend and a vertical section leading to the particle monitor. The results showed that these losses can be high and variable and dependent upon the type of sampler inlet connected, the flowrate through the sampler and the particle size. For example, for the reference probes, losses of between 30 to 60% of the particles entering the sampler inlet plane were found. For the four types of sampling inlets tested piping losses of between 6 to 50% were found.
These losses may have a significant effect on the measured sampling efficiencies of the scaled samplers and so further tests are being carried out to enable the mechanisms involved to be studied, the losses modelled and, if successful, the efficiency results corrected for these losses. This study will also lead to suggestions for improvement of the experimental set-up to minimise these losses.
In the meantime, it is clear that, even without allowance for the particle losses, the scaling works reasonably well for single orifice samplers facing into the wind, such as the CALTOOL and the IOM sampler mounted on the CALTOOL torso.
Longannet coal mine has recently introduced four free steer vehicles (FSVs) underground and, in an attempt to reduce particulate emissions, is operating them on biodiesel fuel derived from rape seed.
To confirm earlier laboratory findings that particulate emissions are reduced with biodiesel, sampling has been carried out underground at Longannet by HSL using a new Personal Diesel Aerosol Sampler (PDAS), developed in the USA and designed to monitor diesel particulate in the presence of coal dust. Monitoring was carried out on two FSVs and at two fixed locations within the production district of the mine and the results compared with those obtained at Welbeck Colliery where similar monitoring was carried out on FSVs fuelled with standard BS EN590 derv.
The Longannet results show that the time weighted average (TWA) diesel particulate elemental carbon concentration measured on the two FSVs was 33 and 39.6 µg/m³. This compared to FSVs at Welbeck where TWA results of 37.6, 42.2, and 65.5 µg/m³ were measured. In both cases the FSVs were carrying out similar duties and on the face of it these results appear to be much the same. However, the ventilation rate at Longannet was less than half that at Welbeck with consequently only half the dilution of the exhaust emissions. Although it is difficult from so few results to make any conclusive observations, the results here are encouraging and, it is reasonable to believe that the airborne particulate concentrations at Longannet would probably have been higher had they used standard derv. From these early results the indications are that biodiesel is helping to reduce mineworkers exposure to diesel particulate.