Controlling dust in underground mines is one of the greatest ongoing challenges for mine operators in South Africa, particularly in coal mines.
Oftentimes, the focus on dust control at mine sites is on the dust that is generated above the ground as it is more visible and prominent. However, fugitive dust from underground mining activities should always be of key concern.
Prolonged exposure to dust particles which are smaller than 10 microns in size (PM10 dust) is proven to cause many adverse health effects such as asbestosis, silicosis and coal pneumoconiosis (black lung disease). This is because these dust particles are so small they can penetrate the lower respiratory tract.
Dust can also affect safety by reducing vision and impairing vehicular traction. Underground mines are already inherently dangerous places to work in. With so much activity going on in such confined spaces, maintaining a clean air supply and clear visibility is critical.
Any risk to health and safety, no matter how large or small, requires innovative solutions to mitigate.
In this blog post, we take a look at the sources of dust in underground mines as well as some of the most effective control measures mine operators should be implementing.
Sources of dust in underground mines
There’s no way to escape the inevitability of dust being generated by underground mining operations. The most extrusive sources of dust are from:
• Untreated haul roads
• Laydown areas
• Materials handling - conveyors, tipping points, crushers etc.
Regardless of which part of a mine site dust is coming from, once it becomes airborne, it becomes a whole-of-site problem that must be dealt with quickly and effectively.
Standard dust control measures in underground mines
As outlined above, underground mines have numerous dust generation points. Because of this, there’s no single solution that can be applied to effectively target every single source of dust. Consequently, mines need to employ a range of dust control measures.
Effective primary and secondary ventilation systems are of utmost importance in extracting or diluting a mine of contaminants such as dust, volatile fumes and toxic gases.
Additional basic control measures such as isolating dust from workers wherever possible, equipping workers with adequate protective equipment like respirators and preventing the formation of dust by watering materials and roads at low pressure are all common practices.
Yet to truly mitigate the risks posed by dust in underground mines, more advanced solutions are required. Ventilation and basic control measures cannot be relied upon solely. Consider a dusty haul road in an underground mine. Haul truck tyres will inevitably churn up microscopic respirable dust which will enter the ventilation system and ultimately be breathed in by workers.
Furthermore, low pressure watering systems are only a ‘quick fix’ solution at best. These systems will prevent coarser dust (10 microns and larger) from becoming airborne and will reduce overall dust throughout an underground mine. However, these systems do not actively subdue dust particles that are already airborne and are unable to suppress PM10 dust.
More innovative solutions for controlling dust include:
1. Utilising advanced dust monitoring equipment
2. Spraying binder products onto haul roads
3. Installing high pressure dust suppression systems
1 - Utilising advanced dust monitoring equipment
One part of the challenge of achieving effective dust control is being able to measure the amount of dust in the air. Otherwise, underground mines have no idea which areas need which solutions.
A dust monitor is a dust concentration measurement system which makes use of the most modern technology available to measure dust concentrations along with wind speed, direction, humidity and temperature in real time.
Dust levels will inevitably rise and fall whenever mining activities are performed, particularly when blasting and drilling occurs. Therefore, underground mines need to continuously monitor the volume and size of dust particles in the air to be able to remedy any spikes in dust levels, especially PM10 dust levels.
There are two key metrics that underground mines should be using dust monitoring systems for:
• TSPM - Total Suspended Particulate Matter. This refers to the total of all particles suspended in the air (airborne dust). The smaller the particles (anything less than 30 microns), the longer the dust will stay in the air for and pose risks to worker’s health.
• Dust fallout - the volume of dust in the atmosphere. This dust will generally land on surfaces. The collected dust sample is expressed as the mass of dust (mg) per cubic meter (m3) of air.
Advanced dust monitoring stations now come with various communications options installed, including radio networks, 3G (GSM) or satellite. This gives underground mines the ability to know in real time the levels of dust concentration and pro-actively implement dust management solutions to prevent localised dust concentrations from exceeding legal limitations.
2 - Spraying binder products onto haul roads
There are a range of spray-on dust suppression solutions available which can be applied to haul roads in underground mines and are much more effective than using water alone. The most advanced solutions are bitumen emulsion binder products.
An advantage of bitumen emulsion, compared to some other materials, is that the bitumen residue remains in the haul road material without leaching.
Bitumen emulsion binder products, such as DASProduct, will form an impermeable seal that reduces dust generation when applied via a series of light dilutions. When used correctly, DASProduct delivers reductions of dust levels of 90+% on haul roads in underground mines.
3 – Installing high pressure dust suppression systems
Unlike low pressure watering systems, high pressure dust suppression systems use low volumes of water at high pressure (above 50 bar) to add humidity/moisture to the air, usually at transfer points such as conveyor belts and tipping areas to capture and subdue dust particles that are already airborne.
These types of systems are ideal in underground mines where it is not practical to pre-wet material, there are challenges with water availability and pooling of water is a concern.
The performance of these systems can be further improved by adding a concentrated surface-active agent like HydroWet to the water spray. This product lowers the surface tension of water particles and makes it easier for the water and dust particles to agglomerate, particularly when managing hydrophobic materials such as coal and other fine ores.
The secret to successful dust suppression is ensuring that the atomised water droplets and the target dust particles are of equivalent size. Spray nozzles need to be exactly calibrated to the right pressure and angle, depending on the type of material being treated. This allows the droplets and the dust particles to combine and fall to the ground, assisted by gravity. If the water droplets are too large, the fast-moving airborne dust will simply flow around them
The benefits of high pressure suppression systems in underground mines include the suppression of airborne respirable dust by 80+%, minimisation of water usage and the prevention of excessive water pooling.
Want to learn more about innovative dust control measures for underground mines? Talk to Dust-A-Side.
Dust-A-Side’s heritage began with dust control solutions in underground mines. For more than 40 years, we’ve been world leaders in total dust control management.
To learn more about our cutting edge dust control services, call us on +27 (0) 12 648 8900. Or you can get in touch by clicking here.