The major threats to safety in the mining industry are toxic gases, fire and dust. The South African mining industry can improve the safety of mine workers by choosing robust, reliable equipment to monitor environments, detect hazardous conditions and utilize the information to act pro-actively.
Challenges include early detection of fires, monitoring of explosive atmospheres and the optimising of ventilation system performance.
The SL2010 Telemetry System provides underground data collecting and communication via the mine’s fibre-optic backbone to the control centre where data logging, alarming, displaying and reporting takes place.
Various sensors can be used to monitor conditions and the information can then be used by the safety and health officials to ensure all conditions are at healthy levels.
The network is based on LonWorks ® technology and implemented as free topology. It is custom configurable and expandable based on specific mining requirements.
The SL2010 solution captures, stores and displays data and information is available by remote web access.
Air temperature and humidity are very important parameters to manage heat stress, and are monitored continuously especially at the mining faces where large concentrations of workers are present and ventilation is sometimes stressed to the limit.
Air velocity is measured at strategic points to ascertain that the ventilation distribution is functioning normally. Ventilation doors status (open/close) are also monitored to make sure that ventilation doors are not left open, effectively short circuiting the ventilation flow hence cutting off the ventilation supply deeper into the mine. This can cause toxic gas levels and temperatures to rise in areas with high concentrations of workers.
Continuous dust monitoring is becoming increasingly important. Respirable dust (i.e. silica dust particles <7µm) causes silicosis (a form of lung cancer) which most often only shows up in workers after extended exposure and normally many years later.
The present regulation in SA mining is to limit workers’ exposure on an 8-hour TWA basis to 0.05 mg/m3 respirable silica dust. This is presently done by control measurements using sampling and analysis, alongside expensive continuous measuring instruments that measures the total dust concentration. Technology is still a far way off from yielding an affordable continuous monitoring instrument that can be located in a workplace and which measures to that standard.
The single biggest threat to human life in underground mines, are fires. Due to the artificial environment with limited fresh air supply, air quality is very fast threatened by toxic gases and fumes. CO gas and smoke are by far the biggest threats during an underground fire. Therefore, it is imperative that very early detection of fires is assured.
The Sperosens telemetry system is extensively used for fire detection. For this reason, CO gas sensors and smoke sensors are placed along strategic positions along the entire tunnel networks.
CO gas sensors have a full scale range of 200 ppm. Smoke sensors are custom designed using radioactive ionisation – this is the only technology that sustains in the hot, humid and dusty environment over extended periods. Other techniques such as infra-red is prone to fast contamination of optical surfaces.
Special software alarming algorithms are deployed in the control centre computers to distinguish between a real fire and spurious signals from blasting and passing vehicles (in trackless mining).
During an underground fire, the Proto Teams will also install sensors on the telemetry system to monitor the progress of a fire in the control centre. High concentration CO sensors (up to 100 000 ppm), CO2 sensors and temperature sensors are deployed at strategic positions. By monitoring the temperature and content of the fire effluent, the ventilation engineer can judge if the firefighting techniques are successful and if the fire is declining.
Since a fire can sometimes take months to recede, it is economically unaffordable to close a mine down till the fire is extinguished. Hence operations must re-start as soon as it is safe. Again, the telemetry system is used to ensure that no “leakage” of dangerous effluent comes into fresh air supply endangering the workers that continue production of the mine.
The risk of methane explosions in coal mines is usually located around the areas where virgin coal is exposed (i.e. the working face), as well as areas where there is weak ventilation.
Methane monitoring sensors are deployed on mechanical mining machines to monitor the methane content in the air coming from the cutting head. When methane levels exceed 1% concentration, the machine is automatically immobilised, and can only re-start when the threat has been removed.
Telemetry systems are also deployed to measure the air quality entering and leaving a coal mining section (working section). Air flow is measured at the intake to determine that enough fresh air is entering, while air flow, CO gas and Methane gas are measured at the exit side.
Digital telemetry systems are used in coal mines the same as in deep mines to communicate measured data to the control centre.
The running cost of deep mine ventilation systems is the single largest operational expense of the deep mines due to the cost of electricity.
Projects are underway whereby the power to the ventilation fans is reduced (i.e. air speed is reduced) and cooling plant output air temperature is allowed to increase, saving electricity.
The Sperosens telemetry system is used to monitor temperature, humidity, air flow and gas levels at critical positions, and is fed into a complex control system that reduces fan speeds and increase or switch off cooling plant temperatures.
Technology is continually progressing to help address the dangers of underground mining and the complexity of the harsh environments in which the monitoring systems must operate.
Sperosens provides innovation through the design, manufacturing, installation, management and maintenance of safety solutions that enables our clients to focus on their core business.