The recent tragic accident at the Beatrix gold mine where a suspected methane gas explosion took the lives of 12 people once again reinforced tragically the fact that mining is a high-risk industry. It also saw media and government departments declaring that this was another indication of inadequate safety measures in the mining industry.
By coincidence that same week I had accepted an invitation from Anglo Gold and the Spero Group to see what technological changes had taken place over the last five years at the Great Noligwa mine to improve safety, and in particular to lower the risk of underground fires and gas explosions. This visit convinced me that while we have moved on significantly from the days of the Canary and the Davy Safety lamp, no matter what technology and sophistication is put into safety systems, the weak link in the chain is still the individual person, and simple human error can still result in catastrophes.
Great Noligwa is a mine in the Anglo Gold stable and is located near Orkney in the North West Province. Like many gold mines it has had a long operational life and workings today are at depths of around 1900 m below ground. In the mid 1990s it was realised that the telemetry system then installed at the mine had reached the end of its life. The system was an analog system employing frequency division multiplexing and suffered from the following major shortcomings:
* Limitations on the number of available channels meant that the system could not be easily expanded.
* The system was maintenance intensive.
* The system was also relatively inflexible, making it difficult to relocate monitoring points from one level to another.
* The system was not fault tolerant and a single cable fault could result in large portions of the network being rendered inoperable.
The mine itself has an extensive backbone that comprises a standard 4-core electrical cable, two cores being used for power and two for data. The new telemetry system had to be compatible with this but at the same time allow for the future upgrade to other types of cable, including fibre-optic. Another major drawback of the historical telemetry system was that it only supported 0-1 mA sensors, even though the industry standard for sensor interfaces is today 4-20 mA. To ensure that this problem never arose again in future, a requirement for the new telemetry installation was that it would be totally open and would not be restricted to any proprietary type of sensor. The new system would have to support the 4-20 mA and other standard sensor electrical interfaces, as well as the legacy 0-1 mA 'mining standard'. (The 0-1 mA sensor interface has a significant advantage for underground telemetry systems in terms of reduced power consumption. It will no doubt continue to be used for telemetry applications for a long time to come).
After an extended study where mining consultants interacted with Anglo Gold's own engineers, the decision was finally made during 1997 to go with the Spero SL2000 multipurpose telemetry system, which met all the requirements. The on-site evaluation of a prototype of the system included operation over 3000 m of cable and the ability of the system to interact with the existing ECAM radio system. For those not familiar with the Spero SL2000 it is a harsh terrain telemetry system that was developed in South Africa to cope with the extreme conditions typically found in the mining industry. Following the decision to go for the SL2000, things moved very rapidly and the initial system was up and running at the mine by December 1998. Another feature of the SL2000 is that each level in the mine has its own power supply with standby battery, which can operate for 8 h without mains supply.
Spero uses Lonworks for network communications. Shared Ethernet is an option for the shaft backbone. A major task for the new system will be to monitor the cooling fans in the mine, allowing transmission of safety-critical information such as bearing temperature, air speed, CO and methane levels. Each fan can now be fitted with its own PLC with a serial interface to the Spero transceivers. Spero offers a number of different types of transceiver and those selected for this installation include single, dual and four channel analog transceivers, each with one digital input and output.
As for the sensors, while the SL2000 operates to the 4 to 20 mA standard as required by Great Noligwa, it also supports the 0 to 1 mA standard on which many of the mines existing sensors are based. While this mine is currently using the SL2000 mainly with smoke, air velocity and CO sensors, the Spero system can be linked to any type of gas detector and sensors monitoring other important mine parameters such as temperature, humidity and pressure. The system can also be configured to provide monitoring and control of conveyor systems and off-board monitoring of mine machinery using trailing cables. The SL2000 has a practical limit of 1000 transceivers and 4000 sensors per system while per level (or sub-network) it will support a cable network of some 10 km. The Spero group offers a full range of locally developed and imported state-of-the-art sensors with the SL2000.
Acknowledging the problems that the mine had with its antiquated ECAM radios (used by Proto teams) Spero partnered with another local company Grinaker to develop the compact and lightweight SC2000 radio system. This has the radio and modern high-density battery pack mounted on a lightweight bandoleer that the miner can wear around his body and was specifically developed for use with the SL2000 system. The Spero Group can now offer this to the many other mines still using the ECAM system that weighs several kilograms.
The Spero SL2000 system already has a man tracking capability where individual tags would be located in the cap lamp battery and strategically located tracking readers (receivers) linked to the SL2000 communications infrastructure, would report on location. The SL2000 system installed at the Great Noligwa mine can therefore be extended very simply to include man tracking.
Following on from the new telemetry system the next part of the upgrade at the Anglo Gold mine saw the replacement of its man machine interface (MMI). The system in use had been developed by the then Anglo American Research Laboratories and operated under an OS/2 operating system for which today there is limited support. The SL2000 is compatible with a number of common supervisory control and data acquisition (scada) systems - but that chosen by the mine was CITECT, running on Windows NT. For the scada implementation, Spero partnered with Industrial Systems Integrators (ISI), and this scada system has been developed alongside the existing fire detection system operator's MMI so that both are currently running in parallel. The screens and mimics developed appear similar to the old system so that the changeover will be easy to users requiring minimal additional training. Whereas the old system was just a standalone unit, the new scada system has capacity for major expansion and can be networked offsite. ISI is now putting the finishing touches to a database where all the information gathered will be logged for use by the company's MIS system. The new scada system came online during the latter part of 2000.
Returning to the fire safety system this mine has five major sections that are currently being mined. For each of these sections data regarding all smoke, methane and CO detectors can be displayed simultaneously, with colours indicating the status of sensors. An additional feature is that the cable voltage at each network node is also displayed, so that cable faults can be readily located or cable voltage drops can be identified and corrected with voltage boosters.
A complex fire alarm algorithm that runs in the background of the scada controls the fire alarm generation. This algorithm is programmed with data on all blasting periods (during which no personnel are underground but large quantities of smoke, methane or toxic gases may occur) and this data as well as other parameters such as the rate of change of gas level are used to trigger a serious alarm.
The engineers at Great Noligwa believe that with the implementation of the new telemetry and scada systems that everything humanly possible is being done to ensure that safety always comes first. Their biggest fear is that despite their now sophisticated technology it will be a human error or mistake that could still trigger an event that could cost lives. This risk is being minimised by mine management's ongoing programmes to ensure that underground workers are aware of the correct procedures to follow in the event of emergency, but at the end of the day we are all only human!
The in-depth study conducted by Anglo Gold into the optimum telemetry system has resulted in the adoption of the LONWORKS based Spero SL2000 at other mines within the group following the success at Great Noligwa. Other Anglo Gold mines where the SL2000 is either operational or is being deployed include Bambanani, Kopanang, Moab Khotsong and Tao Lekoa mines. In addition to its other extensive features the SL2000 has been proven to operate reliably and effectively in the extremely harsh operating and environmental conditions of South Africa's ultra deep mines.
Spero Group
(012) 665 0317
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