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Safety and health in mines research advisory board Annual review 2007

Introduction

The Safety and Health in Mines Research Advisory Board (SHMRAB) is one of the Health and Safety Executive’s (HSE) advisory bodies and is a sub-committee of the Mining Industry Committee (MIC). It is chaired by Her Majesty’s Chief Inspector of Mines and has members representing employers and employees in the British mining industry. Current members and others who contributed during 2007, are listed in Appendix 1.

Contact details for more information on the research houses and individual projects mentioned in this review can be found in Appendix 2].

Fire and explosion

Failed oxygen hose and cylinder at Mansfield Mines rescue service station

An incident occurred at the Mansfield Mines Rescue Service Centre in February 2007 when an oxygen hose ignited and burst during the recharging operation on a BG4 oxygen cylinder. The incident occurred at a stage in the recharging procedure when the output stop valve from the recharging panel was opened, and resulted in combustion damage being sustained by the hose and connectors. Two cylinders had already been successfully recharged prior to the incident occurring.

Examination of the operating procedure at Mansfield revealed that the opportunity for adiabatic compression heating existed in the system, but only after the first cylinder in a batch had undergone refilling. This was due to the retention of high-pressure oxygen in the charging panel that was subsequently released into the hose once a new cylinder was connected to the panel.

Two other factors were also identified as having contributed to the failure. These were an aluminium bronze check valve, a component that had been identified as contributing to hose failures following three previous incidents at the Rawdon Mines Rescue Service Station, and the BG4 cylinder and valve. In all other service stations, where these items were not used in combination with each other, there had been no reported hose failures.

The major recommendations covered the removal of the check valve from the apparatus, the altering of the charging procedure to depressurise the charging panel between each refilling cycle and the consideration of incorporating hard-ends on to the hoses to ameliorate any heating effects due to adiabatic compression or the complete elimination of flexible hoses from the system. Issues regarding the use of appropriate materials, cleanliness and care in the use of valves were also discussed.

Failed oxygen hose from rawdon mines rescue service

An incident occurred at the Rawdon Mines Rescue Service Centre in April 2007 when an oxygen hose ignited and burst during the recharging operation on a BG4 oxygen cylinder. Unlike the similar incident in February, this incident occurred at a stage in the recharging procedure when the valve on the cylinder to be refilled was opened, but prior to the charging panel valve being opened. Combustion damage was sustained to the internal components in the BG4 cylinder valve, the connectors and the hose. Three cylinders had already been successfully recharged prior to the incident occurring.

This event was the fifth in a series of oxygen hose failures that had occurred over a period of 2 years at the Mines Rescue Service. The evidence seen in this investigation conforms to the pattern of evidence seen in the previous four hose failure events and that two factors have been primarily responsible for the ignition and failure of the hoses. These are:

  1. The BG4 cylinder, when in combination with the aluminium bronze check valve in the recharging apparatus.
  2. An operating procedure that permitted the rapid pressurisation of residual gas in the hose and connectors by high-pressure oxygen from both the charging panel or the BG4 cylinder.

These factors were compounded, in this incident, by the use of an inappropriate hose of lower ignition characteristics than the recommended PTFE lined hoses, which is designed for use with mixed gases and not pure oxygen.

Again recommendations were made regarding the removal of the check valve from the apparatus, the altering of the charging procedure to depressurise the charging panel between each refilling cycle and the consideration of incorporating hard-ends on to the hoses to ameliorate any heating effects due to adiabatic compression or the complete elimination of flexible hoses from the system. Issues regarding the use of appropriate materials, cleanliness and care in the use of valves were also reiterated.

Experimental investigation of oxygen hose failures at mines

A number of incidents have occurred at Mines Rescue Services, where an Oxygen hose failure has taken place during the recharging of Oxygen cylinders. A combination of the recharging procedure; bleed valve component; and other factors were implicated. The aim is to perform experimental work to replicate the conditions causing the hose failures to establish the mechanism.

The initial phase was to design and produce a test apparatus that was capable of operating safely (even during hose failure events) at a pressure of 200bar oxygen. The system includes an automated control system capable of performing a typical number of recharging cycles and also the ability to detect oxygen ignition within the charging hose, so that safe shutdown can occur. This phase has now been completed.

Tests on the bleed valve by HSL's Analytical Sciences Unit have discovered contamination that should not have been present within an 'oxygen cleaned' system. Initial tests on phase two (experimental), which is about to start, will concentrate on determining how important this contamination was with regard to incidents that have occurred.

Further tests will look at other factors including the presence of sintered elements within the bleed valves.

Early diction and fighting of fires in belt conveyors

Research activities within Edaffic will deal with the specific topic of fires in conveyor belts and related ventilation issues. All aspects of conveyor belt fires will be addressed, including fire prevention, early detection, combustion processes, new belt materials and firefighting

Mine environment

Improved gas capture and climate control within high performance workings (to Feb. 2007)

This work examined how arduous climatic and environmental conditions impact on workers, together with investigating how climate issues affect the successful outcome of emergency activities. 

The final report was approved by the EC in September 2007 and a published report should now be available from them. The major findings of the project were included in last year’s SHMRAB report.

Evaluating methods of training of mineworkers for hot inspired air when wearing self-rescuers

A limitation of current training in regard to the use of escape respiratory protective devices is that it does not offer provision to experience a hot air burden and associated breathing impacts. HSE defined a need for an improved training methodology for such devices, and sought information on the tolerability and endurance limits associated with their extended wearing. The research was in two phases:

Phase 1: Development of a hot air device which provides a simulation of the breathing behaviour of a W95 filter self-rescuer (FSR) operating in a carbon monoxide contaminated atmosphere. This work involved thermo-chemical modelling of generic FSR behaviour in specific challenge atmospheres, together with the construction and testing of suitable prototype hot air simulation devices.

Phase 2: This involved undertaking a range of physiological endurance tests to examine how well mineworkers accommodate the hot air breathing effects of a filter self-rescuer whilst making a long duration evacuation. The tests included consideration of the physiological benefits of cooling and rehydration within a staged evacuation process.

The thermo-chemical modelling identified that the air from a FSR at high CO concentrations would be extremely dry and hot. Indeed, it was not possible to reconcile the temperatures predicted by modelling with the breathing simulator temperature limits prescribed by BS EN 404. The possibility is raised that the assumptions made in the EN 404 breathing circuit design for the exhaled air temperature being maintained at 37°C may be invalid. This matter requires further attention. Review of the modelled inspired air conditions presented by a generic FSR suggested that it would not be admissible to reproduce the full range of conditions within a training device. A scoping review was undertaken to confirm which approach should be used for providing a hot air device that would simulate the behaviour of a FSR operating in a nominal 0.5% CO content. Initial studies suggested use of a chemical cartridge carbon dioxide absorbent using proprietary "reactive plastic cartridge" (RPC) technology. Prototype long duration hot air devices were constructed using RPC technology. HSE’s laboratory agent HSL undertook safety testing and characterisation of the prototype hot air device using a breathing simulator. This testing confirmed that the device produced a highly humidified air stream with peak inspired air temperatures within tolerability limits at the anticipated breathing rates. A sufficient number of hot air devices were manufactured for use in the physiological trials. Consideration was also given to possible future use of the device as a training device, with discussions held with interested manufacturers.

The physiological tests provided a clear indication of the benefits of a staged exercise-rest cycle against uninterrupted exercise. Four test protocols were devised to evaluate escape thermal scenarios. In broad terms, if evacuating personnel are unable to cool significantly in the prevailing roadway conditions, then a travelling distance of around 2 km would be consistent with the body core temperature reaching a zone associated with rapidly increasing probability of heat exhaustion. One important finding was that a staged evacuation process involving cycles of moderate pace walking followed by a comparable period of rest has the potential to constrain body core temperature within acceptable limits. In effect, a cycle of exercise and rest ensures the overall level of metabolic heat production is controlled. Providing the roadway ventilation air cooling power is sufficient, it should be possible to limit maximum body core temperature excursions. The application of staged evacuation strategies, involving periodic rest and recovery, requires further consideration with Mines Inspectorate and mine operators to identify any changes in practice and recommended guidance.

Mine emergency support technologies

The central objective of this project is to ensure that European standards and procedures to be used in the event of a mine incident continue to be at the forefront of world best practice. There is a range of new and emerging technologies which can now be utilised in mines, many of which were not available when current Escape and Rescue Regulations were formulated.  The research will address all aspects associated with an emergency, from the infrastructure that is in place at the time of the incident, through to coordinated search and rescue involving mines rescue teams.

Ground control

Geotechnical classification, modelling and exploitation for safe and efficient mine layout and tunnel support design

The technical details of RMT’s and Nottingham University’s work on this Project were given in last year’s report. During 2007 the final report of the Project was completed, presented to the appropriate RFCS Technical Group and accepted. The publishable version of the report was submitted to the Commission in May but does not seem to have yet appeared on the EU Bookshop website.

Development of more innovative support systems for gateroads under the influence of rock stress

RMT’s work on this Project is mainly concerned with development of improved instrumentation for design and safety monitoring of rockbolted roadways and investigations into the use of tensioned and untensioned long tendons. The work on long tendons is supported by an HSE research contract. Some work on improvements to geotechnical numerical modelling and roadway risk assessment is also taking place under this Project. RMT’s work is being undertaken in close collaboration with UK Coal who are also a partner on the Project.

Work progressed well on developing a new sonic extensometer to replace the discontinued commercial systems. Compatibility issues with existing anchors and interfacing issues were resolved and development was completed with 2 months of field trials at a UK colliery. The new system is now being commercialised.

The new SM01 strain meter and data logger was proven in the field at several sites and is now commercially available. However, obsolescence of several major components has triggered a redesign. New firmware has been written and suitable box, face plate and rechargeable battery sourced/designed. It is expected that a new commercial unit will be ready by the end of the Project in June 08.

Two new rib monitoring instruments, a protected wire extensometer and a shear monitoring dowel, were developed and deployed for field trials at UK colliery A where rib monitoring is particularly important. Several improvements were made following these trials and the instruments are now being used routinely in conjunction with newly developed risk assessment procedures to improve safety on gateroad drivage and face retreat.

A new design of mechanical three height telltale was developed for use at colliery A. This allows them to be read with ease in very high roadways. Replacement of the installed base of 3 height ribside indicating roof telltales is underway. Initial results are positive and the principle is being extended to 5 wire extensometers.

Further work was undertaken on the EXBOLT and RRTelltales instrumentation data analysis programs. This software package is currently under trial together with a demonstration remote reading combined telltale and extensometer system at Svea Nord mine, Spitsbergen. 

A "Rib Convergence" software package was written, which provides a database for rib closure measurements. This will be used initially at colliery A.

Extensive monitoring in the new Barnsley seam workings at another colliery (colliery B) has demonstrated significant sensitivity of rock behaviour to rock condition and stress; both horizontal and vertical. This data has been used to develop and apply a risk assessment system tailored to the geotechnical conditions to ensure appropriate remedial support is installed prior to face retreat. It has also been used to develop improved action levels and remedial reinforcement strategy for future developments.

A new set of laboratory test procedures for determining the practical groutability of combinations of flexible tendons and grouts was proposed for incorporation into a revised BS7861 Part 2. Laboratory and field tests with top down systems have shown up a number of problems with mixing and pumping the thixotropic grout. A series of laboratory tests was designed to identify the effects of reduced thixotropic grout UCS on bond strength but was delayed awaiting the availability of test specimens. An underground instrumented trial of the effect of tensioning top down grouted long tendons was completed at colliery A. This utilised the new instrumentation, including the remote reading extensometer system and the data logging facilities of the SM01 unit. No raising of the roof or damage to the previously installed reinforcement was measured during the tensioning process in a previously moderately dilated roof.

Alternative tensionable tendon systems which use "bottom up" grouting and do not rely upon thixotropic grouts are currently being field trialled by UK Coal and others. A problem with strength of non-thixotropic cable bolting grouts was identified and confirmed by a surface mixing trial at colliery A. The manufacturer suggests that this problem has now been rectified.

Increased productivity and safety of European coal mines by advanced techniques, knowledge and planning tools enabling strata control of the face-roadway junction

RMT and UK Coal are both partners on this Project, which commenced in July 2007. The main emphasis has been investigating and finding solutions to the rib control problems being experienced at UK colliery (A). Early work has been involved with identifying the mechanisms associated with a rib fall which occurred in the coalgate of a retreating longwall panel in January 2007 in order to develop strategies to prevent a re-occurrence. This work has been regularly reported to a bi-monthly rib working party at the mine chaired by HSE.

Analysis of the rib fall mechanism indicated a need for reassessment and analysis of remedial rib reinforcement, the reinforcement placed on drivage, choice of roadway drivage horizon and consequently roof reinforcement.  It also indicated a need for better monitoring of the ribs and development of appropriate risk assessment and support management systems for the currently driven roadways and new in-seam drivages at the mine.

The rib fall analysis, which included significant numerical modelling, indicated that remedial long tendon rib reinforcement should be installed in vulnerable areas identified in the gates for safe completion of the panel, that improved rib reinforcement consumables would be necessary for remedial support in the gates of the next panel prior to and during retreat and that improved rib and roof reinforcement would be required for installation on drivage for future gateroads at the mine. The latter consumables would need to be suited to the selected roof horizon (stone or coal).

Four programmes of reinforcement development and testing have commenced;

Development and testing of a large diameter (28mm) steel rock bolt for use in roof and ribs

By the end of 2007, initial installation trials had been completed to prove that installation and handling is possible, the testing to BS7861:1:2007 had been completed satisfactorily and full field trials were planned. The "Big bolt" BS7861 testing programme showed that it complied in all respects except that the plates did not begin to flatten within the specified load range and the Laboratory Short Encapsulation Pull Test bond strength was not achieved with a 35mm concentric bit but was achieved with a 32mm diameter eccentric bit. Underground pull tests are to be undertaken during the field trials and the plate manufacturer is developing an improved plate. 32mm bits should be used underground.

Development and testing of a large diameter (28mm) GRP rock bolt for use in ribs

Two alternative profiles of fully threaded bolt were developed as prototypes by the manufacturer and each was tested according to BS7861-1:2007 (Annex Q) in holed drilled with 32mm bits. The flat form thread performed considerably better than the full form version and work has commenced on a full suite of BS7861-1:2007 compliance tests.

Development/identification of a PUR capsule system which could be suitable for use with rib reinforcement consumables

It has been realised for some time that the use of polyester resin capsules as part of a rib reinforcement system can be problematic due to a number of factors, including;

Numerical modelling of rib reinforcement at colliery A, undertaken under the GEOMOD project, indicated that a minimum yield bond strength of 100kN/m was required for rib reinforcement to have an appreciable influence on strata behaviour, but underground observations (and pull tests) indicated that this may not always be being achieved with the polyester capsule resin system.

It is therefore desirable to find an alternative reinforcement encapsulation system which can be used at the face of the heading without impeding production. A possible alternative is the use of a low viscosity PUR capsule using a 50:50 mix. An appropriate PUR product may be able to provide an improved level of reinforcement, despite the inherent lower strength and stiffness of PUR compared with polyester resin. An initial set of underground pull tests showed that 4 out of 5 dowels installed with pu capsules with 500mm encapsulation produced a yield bond strength of over 50kN (i.e. exceeded 100kN/m). Further trials are planned.

Comparison of the performance of various reinforcement systems in coal

A programme of Laboratory Short Encapsulation Pull tests of various candidate rib reinforcement systems has been designed and commenced. The first part of the exercise was to identify suitable embedment lengths and confinement pressures and to establish a comparison standard in sandstone. An initial set of tests using 22mm fully threaded GRP dowels encapsulated in cementitious cable bolting grout in sandstone and coal cylinders was used to determine these parameters and these  indicated that the main programme in coal should use a 160mm embedment length (as per BS7861-1:2007) with confinements of 1 and 5MPa for each system tested. The full testing programme is now underway.

Advanced drivage and roadheading intelligent systems

This Project commenced in 2007 and both RMT and MRSL are partners.

RMT’s main objective is to develop practical strategies for designing, driving and supporting coal face headings to the necessary dimensions required for modern longwall face equipment. These require, for practical reasons, rectangular roadways which therefore require suitable rockbolt and long tendon support.

Problems associated with face line drivage and support are increasing as they become longer, wider and deeper. UK longwall panel widths have increased from typically 250m to 300m with current plans for 350m. This leads to longer standing times and consequent support issues. Wider face headings are required due to the larger face equipment being used. Typical UK roadway widths are 5.0m for gateroads and 6.0m for facelines, but some faces are now being driven as wide as 8.5m.  In Germany the range of faceline widths is 6 - 10 m.

The main candidate heading strategies for face lines are one pass, two pass or stress relief.

One pass: Typically continuous miners and bolter miners are 5.0-5.5m wide for gate road drivage. For 6.0m wide faceline drivages it is relatively straight forward to drive in a single pass by ‘shuffling’ the machine. However at 8.0/8.5m steering becomes problematic, the floor can be broken up and the rib profile will be uneven leading to strata control issues; consequently, dependant upon site conditions, this option is not always feasible or desirable. 

Two pass system, widening out:  This system is commonly used in Australia where mining depths are typically a lot shallower than in Europe. This is a relatively new strategy for the UK. It has recently been applied at two UK collieries (A & B) in very different conditions and these experiences are being studied.

Stress selief headings: These have not been used in UK or Australia for the last 15 years. They were used in Australia with success but had limited success in the UK due to depth issues. There is renewed interest in both Australia and the UK as they could provide a solution to current problems.

Geotechnical numerical modelling can be used to model these options. The packages expected to be applied are MAP3D, FLAC2D and FLAC3D. Modelling of support geometries, stress re-distributions and likely deformations has been undertaken for both Colliery A and Colliery B.

The recently driven 8.5m wide faceline at Colliery A was planned to be driven in a single pass. The two previous 8.5m wide facelines in the same area of the colliery had been undertaken successfully. However, conditions on this third faceline proved to be difficult with large roof deformations occurring rapidly. FLAC 2D modelling was undertaken to assist with assessing the option of continuing drivage at 5.2m and then widening to 8.5m. This suggested the option could reduce roof displacements by about 30% for the 5.2m wide heading although the height of softening would not be reduced. There was some indication that the newly exposed roof of the widened roadway would be less broken than the initial drivage, suggesting that widening out on the face side would be preferable. The actual experiences of driving this faceline are now being assessed. The seam model is being updated with a view to modelling the next face drivage with a 3D model to allow improved analysis.

At Colliery B, a study of the ground conditions has been undertaken for the primary support design of a 8m wide faceline driven in two passes. Here the motive for two passes was improved drivage speed rather than strata control. The FLAC3D model runs simulated the two stage excavation by initially excavating and supporting at normal width, running the model until stability was achieved and then excavating and supporting the additional width. Unlike the situation for Colliery A, this faceline is orientated in the most favourable direction with respect to the direction of maximum horizontal stress.  No long tendon reinforcement was included in the model.

The model results for drivage at the initial width, at two alternative lateral stress levels, showed small roof displacements with softening within the bolted height and the bolts well loaded. With the lower lateral stress of 11MPa, widening to 8m had little effect on the roof. With the higher lateral stress of 15MPa, widening resulted in a large increase in roof movement and softening well above the bolted height indicating a need for cable bolting.  Consequently it was recommended that if monitoring results during initial drivage showed conditions with minimal roof movement then the modelled support should be adequate for widening. If monitoring shows softening within the bolted height during the initial drivage it was probable that cables would be required when widening. The lowest risk option would of course be to cablebolt prior to widening. Again, the actual drivage experience is being assessed and compared with the modelling. Plans at the mine are to drive future face lines across the maximum lateral stress direction and the consequences on support will need to be considered.

MRSL’s research is primarily associated with assessing the feasibility of unconventional rock fracture methods within manless, automated excavation schemes, involving the development of a) models of electrofracture mechanisms, b) a techno-economical understanding of the technology and c) the concept of manless mining in an inertised atmosphere.

A number of relevant patents were identified concerning unconventional rock fracture, involving the following companies: Caterpillar Inc., Hitachi Zosen, Itac, Maxwell Labs. Inc., Noranda Inc., Placer Dome Technical Services Inc., Pulse Sciences Inc., and Tetra Corporation.

Significant developments were found regarding efficient, compact rock fracturing or drilling apparatus within the hard-rock mining and military technology sectors. Early cited techniques employing thermal stress induced by dielectric or induction heating are low efficiency and are ore-specific.  Other comminution pre-treatment mechanisms include microwave heating induced fragmentation. To increase the effectiveness of rock breakage, enhancements have employed plasma-hydraulic shock/acoustic fracturing (where a shockwave or pressure wave is derived from an underwater discharge or plasma). Further refinements based on shallow electrode electrical discharge techniques also appear promising. The efficiency of these physical processes is such that individual discharges of the order of 50kJ, can fragment rocks of several tonnes mass. The on-going research will include an evaluation of the safety controls necessary when considering novel fragmentation technologies, in particular pulse electrofracture techniques. 

MRSL studies also involve the ergonomic assessment of mining machinery, where new design guidelines are being prepared in order to minimise health and safety risks and to improve the operational efficiency and reliability of roadheader operations.

Prediction and monitoring of subsidence hazards above coal mines

This project commenced in July 2007. RMT, UKCoal and MRSL are all project partners and Nottingham University have been subcontracted to develop improved surface subsidence prediction techniques. The Nottingham University subcontract did not commence until late December 2007.

RMT’s work on this Project concerns sub surface subsidence and disturbance of the strata and is particularly involved in studying the circumstances of water inflows into working mines from the surface, seabed, aquifers and old workings and in improving our understanding of how to work longwall panels above old worked areas. This is relevant to current and planned workings at 2 UK mines.

Historic and case study data on water inflows into working longwall panels due to mining induced permeability were obtained and this is now to be collated and analysed. Considerable historic data has been obtained from the UK Northumberland and Durham coalfields, pre 1980. Significant research was undertaken into water inflows in these mines during the 1960s and 1970s, culminating in important work by Garritty and Newcastle University funded by the ECSC programme. Three major sets of water inflow incidents have occurred in the UK over the last 25 years, and data from these cases in the Selby coalfield, N W Leicestershire coalfield and Northumberland is being gathered. International criteria for preventing water inflows from water bodies have been reviewed.

Work has also commenced on the problems associated with mining above previous longwall panels though this was not due to commence until next semester. Current and historic practices have been reviewed and case studies identified for data collection and analysis.

MRSL's research has three major components - the monitoring of shaft fills, in order to provide advanced warning of subsidence and consequential risks, field studies of problematic Coal Authority shafts and immersion tests on shaft fill and shaft lining materials. 

The study of shaft fill settlement has examined the possibility of using a draw-wire sensor as a linear displacement monitor to gauge the height position of the shaft fill. Either a pawl and cam assembly or a magnetic vane sensor are the preferred options. This part of the work also reviewed alternative telemetry and data-logging systems to those currently used by the CA, with the purpose of reducing operational costs, improving performance and allowing on-line transmission of data to interested parties from remote locations.

The immersion tests follow on from the tests which were begun within the Waterchem project and which finished during 2007. A wider range of shaft fill and shaft lining materials are being investigated, with these being linked to specific problematic CA sites in Lancashire, Yorkshire and, possibly, the North East. Materials to be assessed include basalt, cast iron, reconstituted aggregrate, steel reinforcement, limestone and concrete.

Mine communications

Enhancing the performance of mine communication and warning systems

This project was concerned with achieving improvements in the performance of speech communication systems and auditory alarm and warning systems across a wide range of underground and surface mining applications, together with appraising the application potential for power line communications in mining. The final report was approved by the EC in May 2007 and a published report should now be available from them. The major findings of the project were included in last year’s SHMRAB report.

Researching the applications of innovative open wireless technologies

The main objective of this research is to enhance mining operations through the widespread introduction of advanced wireless network technologies, including smart open wireless sensor networks, wireless digital voice communications and wireless position tracking systems. The other UK partner in this project is RMT.

MRSL’s research during the last year largely involved the following:

Wireless platform technology development

Work continued in respect of developing a common wireless technology platform which will lend itself to various underground safety and operational support applications. Given the extended product life cycle requirements of ATEX certified equipment, there is a need for open standards based technology. Of the various wireless platforms evaluated, there is an identifiable segmentation emerging between low data rate personal area networking which has largely adopted IEEE 802.15.4/Zigbee technology, and WiFi, which is used for broadband communications. This situation is reflected in the United States and Australia, where there is a similar impetus to introduce and exploit these new technologies. Research continued in respect of adapting and revising Zigbee radio and control software for use in high resilience underground applications.

Development of a Zonal Tracking Demonstration Scheme

The use of LR-WPAN technology to provide an active tracking and location capability as an alternative to conventional RFID (transponders) has been advanced as a priority. The low power radio nodes are also used to collect and telemeter vital signs and status information. Work is in progress to equip CSM’s Holman’s Test Mine with a large mesh of wireless nodes. The radio technology uses EmberNet LR-WPAN mesh networking technology and the latest Zigbee stack, which supports monitoring and safety applications, by including a network transport layer, message acknowledgements and support for large, dynamically configured mesh networks. The demonstration scheme will permit ~40 miners to move about the workings, with their individual locations logged as they pass fixed low cost wireless network nodes. The location information is transmitted across the mesh network and inputted into a central (SQL) database. Location information is also stored locally in data collection points, which allows miner location information to be retrieved even where significant infrastructure damage may have occurred. A dedicated interface has been developed to offer real-time access to the central database and provide a graphical interface to visualise the location and status of tracked mineworkers.

Mine operations

Optimisation of minewater discharge by monitoring and modelling

The overall objectives of this research were to offer solutions for effective mine closure, improved knowledge of ground water movement for working mines and effective surface environmental control of factors resulting from mining activities, both past and present.

The final report on the project was submitted to the EC and finally approved in November 2007. The final published report should be available from the EC in early 2008. The major findings of the project were included in last year’s SHMRAB report.

Failed rubbing ropes

A metallurgical examination was requested to determine the failure mode of two ropes and to assess whether or not the shaft environment had been a contributory factor since the shaft had been disused for some time before the ropes failed. The results revealed no evidence that the ropes failed as a result of manufacturing features that were present when they were installed in 1987. The evidence indicated that the strength of the ropes before they failed could have been reduced by at least 71% due to corrosion of the outer wires. The nature of the corrosion on the wires was consistent with exposure to acidic strata water following the progressive loss of protection provided by the zinc coating and the rope grease. The level of corrosion found on the ropes did not provide a full explanation for the failures and other possible failure modes were assessed. An incident report was prepared for the inspector and this project is complete.

Increasing the Efficiency of Roadway Drivages through the Application of Advanced Information, Automation and Maintenance Technologies (IAMTECH)

The aim of the research was to improve the efficiency of roadway drivages, through the use of the latest advances in information and automation technologies, applied to:

MRSL's major contribution to this project involved studies on the selection and evaluation of wireless technologies and investigation of underground propagation. Other work undertaken during the final year considered the feasibility of ‘robotising’ the drill rigs that are fitted to continuous miners.  Modelling exercises were performed, utilising a Joy 12CM18 machine, to examine how the installation of captivated tracks could allow roof and roadway-side bolting rigs to travel to positions determined by the on-board programmable logic controller. The study examined proposed layouts and mechanical forces, using a Hydramatic S4200 Roof Bolter with positioning universal joint shaft and rams.

Despite the principles proving feasible, however, both machine manufacturers and mine operators appear unlikely to support further developments.

Advances in exploration methods and applications

In addition to MRSL, other UK partners involved in this project are UK Coal, Heriot Watt University and Seismic Image Processing. The project seeks to enhance mining exploration and planning capability through techniques such as seismic surveying, radio imaging through coal panels, drilling parameter analysis and micro-seismic monitoring.

MRSL’s research is concentrated on determining the factors that may have limited the scope of deployment of RIM in the UK, and whether significant enhancements are possible.

In the UK, the coal has an unusually high electrical conductivity and, at the same time, a low contrast in conductivity between the coal and the boundary rocks. It now seems that, in these circumstances, lowering the operating frequency to achieve a higher penetration of the coal has the unwanted side-effect of a deterioration in the ability to distinguish between in-seam and out-of-seam anomalies. To counteract this, MRSL has been studying signal processing techniques that may allow the technique to work at a higher frequency. A patent has been filed regarding certain aspects of the signal processing.

In addition, a study of antennas has led to the development of two novel types - one is based on the use of specialised ceramic tiles which concentrate the electric field; the other is based on the use of plastic electrodes or foam pads (both using electrically-conductive materials) attached to the rib-side wall. MRSL has filed a patent describing the use of such items. An interim conclusion of the project is that RIM could usefully be enhanced by replacing its portable loop antennas by an array of such electrodes, supported by advanced signal processing. This would have the additional effect of reducing the spurious signals borne by the mine’s metallic infrastructure.

Equipment is being built to test these assertions, and it is hoped to do some experimental work underground in the final stages of the project.

New mechanisation and automation of longwall and drivage equipment

The project focuses on the development of full automatic shearer face equipment. This will take into account development of software for the design of cutting tools with a minimum of pick wear and machine down time due to excessive vibrations. Innovative methods of maintenance and planned repair of the machines are also features of the project.

The MRSL research into oil contamination monitoring concluded that both twin-plate and thin-film dielectric capacitive methods seem most promising, along with infrared absorption. Six sensors were recently obtained, in order to undertake comparative evaluations. A test rig was commissioned at Mansfield and experimental work will start in early 2008. As a separate part of this study, methods of actually removing water contamination from lubricating oils was examined and limited-scale laboratory tests will take place during the next year.

Research is being undertaken, in conjunction with partners from Poland, regarding maintenance limitations on coal face machinery. Software for maintainability and human reliability assessment tools was developed and preliminary evaluation and testing exercises are about to commence.

RMT’s work on this Project is focussed on developing improved techniques and tools for designing mechanical cutting drums used in coal mining machinery. This will cover roadheaders, with axial and transverse heads, shearers and continuous miners.

This work is being addressed through fundamental numerical modelling of the cutting process using FLAC 3D, analysis of selected case studies and developing an improved software package based upon the software originally developed by British Coal in the 1980s and incorporating a modern user interface. The Project is mainly oriented towards improved production performance and reduced costs of cutting rather than Health and Safety.

Improving mining transport

The project addresses a range of novel approaches to improving the performance, reliability and environmental aspects of operating transport systems underground in deep, extensive coal mines with complex networks.  The use of alternative motive power provisions for transport vehicles will be investigated, by examining the potential for using alternative fuels, including fuel cells. The study also encompasses transport logistics and the potential merits of using advanced management information and machine diagnostic systems. In addition, the safety and health aspects of machine fires, exhaust emissions and whole body vibration are included.

The motive power studies undertaken to date have concentrated on acquiring information regarding diesel replacement biofuels and fuel cell technologies, in conjunction with project partner Rittal from Germany. Various mining related transportation projects involving fuel cells, conducted in association with the US Department of Energy and NIOSH, have been reviewed.

MRSL’s involvement in studies into ‘Enhanced Transport Diagnostics and Management Information Systems’ comprises development of Wonderware’s InTouch SCADA software. Work has commenced to monitor and control all of the underground plant and mine environment via InTouch, in conjunction with UK Coal.

A further part of this project is the development of an on-board engine compartment, cab and wheel-arch fire-fighting system, which can be periodically tested and yet still maintain operational capability. Two redundant FSVs have been made available by UK Coal for surface tests and the vehicles are being prepared for testing. Ancillary water supply equipment and nozzles are being sourced.

Shaft switch suitability

HSL were asked to review the current guidance and standards for safety control systems for machines and relate the relevant parts of these documents to the issues identified in the above incident investigation.

A report was issued in August 2007, which covered the guidance and standards that should be applied to position sensors, control systems and software. A tabulated reference guide / aide memoir was included in the report.

The main findings were that there are no specific standards for control system design and safety switch selection, for the prevention/detection of shaft intrusions. New machinery standards follow the BS EN 61508:2002 series approach, applying a safety integrity level to the machine, which the control system and safety switches have to meet. Whilst there are difficulties trying to back engineer a 20+ year old system to comply fully with this approach, it should be possible to identify areas that do not follow best practice.

The recommendations were as follows:

In accordance with the selected SIL:

The recommendations of the report were strongly emphasised to the industry at the Safe Manriding In Mines (SMIM) meeting in October 2007.

Shaft key failure at a large miscellaneous mine

This project has involved the examination of part of a failed driveshaft and eight failed bolts taken from a winding engine. A large scab of material had broken from the side of a large keyway in the driveshaft as a result drive had been lost to the winding mechanism and there had been an un-anticipated descent of a cage during a routine test cycle. As I understand it there were no personnel in the cage and nobody was injured as a result of this dangerous occurrence.

The HSL investigation is considering the modes of failure of the driveshaft keyway and the bolts. The H&S Inspector asked for an urgent verbal response on the drive shaft failure because information was needed as to whether other driveshafts in the same drive train needed to be inspected/replaced prior to re-commissioning of the winding engine. This response was provided before Christmas. Other work has been completed on the mode of failure and material of manufacture of the bolts, and further possible work had been anticipated on provision of further evidence (the key from the keyway) by the Inspector.

Mine hoist ropes

HSL were asked to ascertain the cause of failure of a 4 rope lift. The lift in question failed in service and was destroyed, but fortunately no one was injured.

Objectives:

Main findings:

  1. The ropes were 16mm nominal diameter, with an 8x19 (1-9-9) Seale construction, dual tensile grade 1320/1620 with a right hand ordinary lay, as defined in ISO 4344: 2004.
  2. Each of the four wire ropes was heavily corroded over a length of approximately 3.5 - 4.5 metres. The remainder of the ropes appeared to be in a reasonable condition and serviceable.
  3. The ropes had failed by a combination of wire thinning by corrosion and wear, and ductile overload of the remaining wire cross sections.
  4. The corrosion and wear had been caused by inadequate lubrication, and dripping water leaching away the lubricant. The predominant degradation mechanism was corrosion, assisted by wear.
  5. Tensile load testing of the four well-greased sections of rope that were supplied, was carried out and the ropes failed between 112.8 and 118.6 kN. Tensile load testing of two of the corroded and ‘undamaged’ sections gave failure loads of 79.9 and 102.8 kN. The specification minimum for this type of rope was 106kN. All the well greased samples tested were greater that the specified minimum strength stated in ISO 4344: 2004. The two corroded samples were below the minimum specified breaking force, and the worst rope section was 25% below the specification minimum.
  6. Measurements of the fracture areas indicated a loss of rope cross sectional area of between 82 and 90% due to corrosion and wear. The actual static Factor of Safety was calculated to be 3.7 for each rope, which represents a cross sectional area of 73%. The Factor of Safety had therefore been eliminated by corrosion and wear. 

Assessing the degradation of mine winding suspension gear

Components used to suspend cages and skips in mine shafts are subject to inspection at prescribed intervals. Suspension gear components can degrade by a combination of wear, corrosion and fatigue. The object of a statutory inspection is to assess the level of degradation against given criteria. The current assessment criteria, which were written in 1980, give acceptable levels which were derived empirically rather than being calculated by stress analysis and/or fracture mechanics. The objective of this project is to derive criteria for acceptable levels of degradation using stress analysis modelling and fracture mechanics principals. This will enable more objective inspection and assessment of worn or corroded suspension gear components. This project is currently in progress with models having been developed for typical levels of wear and/or corrosion and typical stress and mine winding cycles.  The results will be compared with samples of suspension gear components, which have been rejected when assessed against the current criteria.

Failed hinges from a gypsum mine

A metallurgical examination was requested to identify the failure mode of a weld that had attached a hinge to a continuous miner. The failure mode was identified as fatigue consistent with loading that was reported to have occurred at the time of the incident. A letter report was prepared for the inspector and this project is complete.

Appendix 1 - Members of SHMRAB 2007

Others who contributed to SHMRAB meetings during 2007

SHMRAB Secretariat
HM Inspectorate of Mines
Health and Safety Executive
1.2 Redgrave Court
Merton Road
BOOTLE L20 7HS
UK

Appendix 2 - Contact details for researchers mentioned in this review

Updated 2013-03-06