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Safety and health in mines research advisory board

Annual Review 1999


SAFETY MANAGEMENT

Material Transport System

IMC are undertaking a study, partly funded by the ECSC, into 'Operational Risk Management for Transport Systems'. The overall aim is to provide guidance to improve the operational efficiency and safety of mine transport systems. With the ever-increasing quantities of materials and distances over which they must be transported, the efficiency of the haulage and transport operation of a mine is closely linked to the overall viability and profitability of the mining operation. In addition, haulage and transport operations are commonly associated with high accident risk. In terms of both financial efficiency and safety, therefore, material transport constitutes a major consideration in the overall business risk.

The study is intended to address these limitations by developing a practical, user-friendly, technique for the identification and evaluation of total business risk which will be equally applicable to the planning of new transport systems and the improvement of existing operations.

Studies have started at a high production colliery which uses a range of locomotives, free steered vehicles and belt systems for personnel and material transport. Research has focused on identifying hazards which limit efficient and safe performance, identifying controls that reduce the risks arising from the above hazards, and collating quantitative data on the factors that influence economic performance. This information includes production delays, machine/equipment damage, installation, maintenance and repair costs.

A method of investigation has been developed and is being used in the mine-based research to identify the hazards and risks that can arise as a consequence of human error potential resulting from poor ergonomics and the failure to consider the human factors which influence the man-machine interface. Factors being addressed include restricted vision, poor lighting, inappropriate control response relationships, and the impact from adverse environmental conditions and ill-considered working procedures.

The Use of Virtual Reality for Mine Operation and Safety

Nottingham University, HSL and IMC are partners in this new ECSC project. The HSL work begun this year focuses on the use of virtual reality (VR) techniques to enhance safety in mines. In particular, HSL will investigate the practicalities and value of using VR for the safe planning of the installation of mine equipment and the usefulness of VR as a tool in the investigation of mine accidents.

Progress has been made in collecting available dimensional information and computer aided design data on equipment used in mines, for inclusion in the virtual model of the mining environment (the virtual world). Mining equipment manufacturers and collieries have made some model and design information available and more is being sought. Discussions with Mines Inspectors are helping to identify a series of accidents/incidents which are thought to lend themselves to VR modelling. Three software tools for building virtual mine layouts have been obtained and these are being investigated alongside virtual models of mining equipment and miners. There are issues of compatibility to be addressed in trying to amalgamate the various components of the virtual world.

A detailed review has been undertaken into the application of ergonomics and remote control technology in the international mining industry. This review will conclude early this year with a study of the potential application and interaction of the findings with virtual reality technology. It is planned that these findings will be taken forward into the development of selected VR models that will have practical benefit for the industry.

IMC's contribution is a small study of the potential application of VR to the ergonomics of mining machinery, particularly in the field of remote control.

Alarm and Evacuation Systems

University of Nottingham and IMC have started work on this new ECSC research project aimed at improving alarm and communication systems reliability and to develop emergency and evacuation strategies, adapting the main mining methods used in EU. Also, virtual reality tools are to be developed for testing the evacuation strategies and training workmen implicated in emergency and evacuation situations. The main objectives include:

SAFETY ENGINEERING

Underground Communications

IMC research, part-funded by an ECSC project 'Improvement of Efficiency and Reliability of Underground Communications', has the objective of improving communications underground, particularly for isolated workers and in an emergency situation. The central premise of the work is that recent developments in communications techniques and device technology permit signals to be superimposed on the existing mine cabling network, largely avoiding the installation of dedicated cabling. In progressing these objectives, it is becoming apparent that mains borne networks can have a wider range of application than first thought and may offer a viable alternative to a dedicated digital network. The approaches to the work, whilst aimed at overcoming the problem of widening the coverage of person-to-person communications underground without incurring high infrastructure and installation costs, have the potential to address other communications tasks. These include command telemetry to remotely activate electrical and electro-mechanical plant, collecting data from distributed environmental sensor arrays, and relaying detection information from transponder interrogation points. In principle this should offer wider in-mine coverage with lower infrastructure costs.

Concerning the field measurement programme, results along underground power distribution cables show that induced signals into HT power cables are only partly suppressed at earth clamp points and transformers. As predicted by modelling, signal energy and power budget is periodically divided as it branches out through the mains network; nevertheless, useable signal levels are measured at the extremities of a typical mine network.

Prototype equipment has shown that, with a high efficiency coupler and power line modem chip-set, the system offers high immunity to electromagnetic interference and mains borne high voltage spikes. The characteristics of power line "noise" are dominated by intermittent/random voltage spikes with short decay periods, mainly caused by imperfect switching circuits. Power line modem manufacturers have developed sophisticated internal circuitry to minimise such noise which is being exploited in this work. These commercial devices primarily rely on processing transmitted signals in the electrically quiet (minimum disturbance) parts of the 50 Hz mains cycle, e.g., zero or minimum current periods. Work on developing power line modems is being undertaken by SGS-Thomson, Siemens, and National Semiconductor, which is likely to provide low power devices suitable for intrinsic safety applications.

The development of an inductively coupled stray flux from the mains cables to power a local modem node is continuing. The difficulty is to optimise the voltage coupled and the storage battery arrangement. The demonstration of a local radio hub, with low power radio modules, is on going. The intention is to connect the radio hubs to power cable inductive coupled nodes and operate a through transmission system. If strategically placed, a working distance of a 100 metres line of sight is feasible. Working conditions underground cause considerable, and difficult to predict, variations to the typical propagation range. Hence tests are being conducted with diversity aerials arrangements at different node locations.

Safety of Workers around Mobile Plant

The objective of this project is to investigate possible approaches and technologies to improve the safety of workers in the vicinity of mobile plant. The work programme is a component of an ECSC research project and will address problems that exist in quarry operations, factories, warehouses and underground mines. The first phase of the work has involved the review and examination of underlying accident factors, possible ergonomic assessment methods and vehicle retrofit improvements. Subsequent phases of the work are concerned with examining personnel proximity detection, location and warning annunciation methods and the underlying principles of a practical scheme are to be demonstrated.

Beyond the modification of vehicles to improve ergonomics and the fitment of cameras, there is a need to provide an effective means of arresting or inhibiting movement of the vehicle where the driver has failed to notice a worker in the vehicle's proximity. Such a system must respond both to situations where the machine is approaching the worker at speed, and, where the machine is about to start and the worker is already in close proximity to the machine. This requires a proximity or location system with a wide range of measurement distances, possibly from 1 to 20 metres from the machine, with uniform coverage around the machine envelope, accepting that the range sideways on to the machine may be reduced.

The principal research difficulty is to determine what form of proximity detection will function in a variety of environments, in close proximity to the machine and other substantial metallic infrastructure. Several possible approaches have been examined. A detection method which is considered feasible is the use of specialised electromagnetic location techniques. The use of extremely low frequency (ELF) magnetic dipole location techniques in conjunction with advanced RF/ID techniques is considered to offer good technical potential, largely because a range of 20 metres or more is possible and detection is less influenced by the surrounding machine metalwork. Hence RF/ID and ELF magnetic dipole systems will be the focus of ongoing research and development, with demonstration planned in the latter half of 2000.

SLACK ROPE PROTECTION

Slack Rope detection was a major recommendation of the Safe Manriding in Mines Reports published in 1976 and 1980. During the early 1980's trials were performed but proved unreliable and inclusion of the device signals into the emergency trip system was not encouraged. The system has traditionally included shaft signals and communication. The latter has had several problems over the years but is now considered to be in a more reliable form.

This project was set up to further pursue improvements and reliability aspect of slack rope protection. It was also decided to pursue inclusion on multi-rope friction winding systems to take advantage of detecting over-load conditions and equalising rope tensions. It is a collaborative project involving Davis of Derby Ltd, Barker Davies Ltd, RJB Mining (UK) Ltd, Midlands Mining Ltd with some HSE pump-priming funding.

Areas being studied include:-

There have been some problems with sealing arrangements for the amplifiers and strain gauges and the fixing of the strain gauges to the suspension links. There have also been operational problems associated with the closure of one of the mines involved in the trials being announced during the project. Field trials of the internally bored suspension link for drum rope winding systems are continuing at another mine.

A design, developed as part of the project, involves a compression load cell for friction winding systems. An initial design has been tried at a third mine and the results have been encouraging with the cell retaining its original calibration over a considerable period of time. This trial is continuing using the compression type cell and because of the encouraging results, a similar device is being developed for drum winding systems to replace the strain gauge design. The final report is expected from the lead contractor, Davis Derby, early in 2000.

Engineering Critical Assessement of Mining Cage Suspension Components

The aim of this HSL project is to provide information which will enable engineering critical assessments to be made of mine cage suspension gear. This involves looking in detail at the non destructive testing procedures and the application of fracture mechanics techniques to selected components.

A literature review, consisting mainly of evaluating the current guidance on the examination of cage suspension gear, as contained in the NCB document "Procedure for examining cage suspension gear at test centres", has been completed. A list of detailed comments has been compiled and additional comments have been obtained from industry during the site visits. In addition, HSL archive papers on cage suspension gear have been assembled and reviewed.

The four companies (two manufacturers and two test centres) currently active in the examination of cage suspension gear have been visited to assess current practice. A rejected cage suspension chain was obtained during the visit to Ormerod; this was brought back to HSL for examination.

Suitable NDT testpieces of the same material have been manufactured and pre-cracked in fatigue. A total of 12 four point bend testpieces (width 50mm and thickness 20mm) were machined from a BS 4360 Grade 50D cross-rolled steel plate. It was decided that final crack depths of the order of 1mm, 2mm and 3mm would be appropriate for NDT standards and four sets of three testpieces have been prepared.

Several items of cage suspension gear have been assessed to establish the threshold defect size to initiate fatigue cracking:

  1. Cage hanger - it was established experimentally that 7mm deep defects were required to initiate fatigue cracks in rectangular section (100 x 40mm) cage hangers. Cracks of this depth should be readily detectable by most NDT methods.
  2. Balance rope swivel - it was calculated that threshold fatigue crack depth in the balance rope swivel was of the order of 14mm (compared with a swivel diameter of 95mm). Once again, cracks of this depth should be readily detectable by most NDT methods.
  3. Rope socket pin- preliminary assessment indicated that the threshold crack depth for fatigue crack growth is in the range 1 - 2mm for an 80mm diameter pin with a span of 114mm. This would obviously present a much greater challenge for the NDT technique, compared with the previous two items, but ought to be achievable under good conditions.

Future work will involve further detailed assessments of cage suspension components and the examination of life-expired equipment.

Forward to:

Updated 2009-05-22