Coal dust is a continuous concern at Australian coal mines, necessitating improved controls to protect worker health as well as driving environmentally friendly innovations to control and mitigate dust levels.
Respirable coal dust is generated and released into the air through several different mining processes, including breaking, crushing or milling ore; coal combustion processes; and handling and transport of coal and coal fly ash.
Shutdown maintenance activities and cleaning of workplaces where coal is used can also generate dust.
Respirable dust is very fine dust — generally 10 or fewer microns in diameter — that can reach the lower regions of the lungs and cause occupational or mine dust lung diseases.
According to Safe Work Australia, workers can develop coal workers pneumoconiosis by breathing in coal dust, often in large amounts, over a long period of time.
Workers in the mining industry or anyone who is exposed to coal and dust associated with mining work are at risk — coal workers’ pneumoconiosis is also an increased risk for workers if they smoke.
The generation of dust caused by mining activities can also create a constant safety hazard on sites, which can be minimised by wet drilling or fitting drilling machines with dust collection devices.
In July, the NSW Resources Regulator issued a warning to coal mine operators after levels of respirable dust nearly four times the acceptable limit were recorded at a NSW open-cut coal mine.
A dozer and grader operator at the mine recorded a respirable dust result of 4.8 milligrams per cubic metre, far above the relevant shift-adjusted occupational exposure limit of 1.37 milligrams.
No unusual exposure conditions were specified by the worker, and they were not wearing any respiratory protection during the exposure period.
The regulator reminded mine operators to ensure the highest level of controls, and that education and training of workers were in place to prevent exposure of workers to the hazards of respirable dust.
It added: “The order in which controls are implemented must follow the hierarchy of controls — personal protective equipment is the last line of defence against exposure.”
Measures for dust control
Control measures to manage dust include fitting drills with water injection or dust extraction systems, positioning ventilation to blow dust away from workers, and controlling dust at the source with a cyclone sample collector and during crushing and sample splitting.
Controlling dust at the source requires consideration of each crusher, mill, and grinder, with dust control devices fitted at the primary crusher feed hopper, as well as secondary and tertiary crushers plus screens.
Other areas that may require dust control measures include conveyor belt transfer points, stockpile stackers and reclaimers, and during loading and unloading operations.
An indispensable part of any dust management plan is the implementation of dust monitoring to optimise control strategies.
Obtaining dust samples ensures exposure is effectively controlled, provides data for reporting obligations, and helps determine dust behaviour, distribution, and properties.
Typical techniques for dust sampling and measurement around the world include sampling from still air, mass concentration measurements, continuous real-time monitoring, and personal sampling.
In New South Wales, personal gravimetric sampling is the approved method used in coal mines.
This method collects inhalable dust from the air close to a mine worker’s nose and mouth during a full shift, which is then measured and weighed.
For underground coal mines, ventilation is integral to managing air quality and dust exposure and can be improved through several methods.
These methods include installation and maintenance of a gob curtain, face ventilation, ventilated cutting drums, blowing face ventilation, and exhausting face ventilation.
Face ventilation is the process of providing air to dilute and carry airborne dust down a longwall face and prevent it from coming into contact with mine operators. Ventilated cutting drums reduce the amount of dust created by a longwall shearer through water-powered dust capture tubes built into the hub of the shearer drum.
Blowing face ventilation involves blowing clean air toward the longwall face and returning contaminated air through the ventilation system, while exhausting face ventilation uses clean air across the face but then draws contaminated air behind a curtain or through exhaust tubing.
Environmentally-friendly innovation for dust suppression
A study published last year explained that current methods for dust suppression fell into either physical or chemical methods, with the first involving suppressing dust by covering it with cloth, a dust control net, or watering, whereas chemical methods use environmentally friendly dust suppressants.
The authors said: “Due to the suspension and hydrophobicity properties of coal dust, chemical methods are more efficient than physical ones in dealing with respirable dust.
“Chemical dust suppressants, which capture dust particles in the air through the application of chemical substances, can eliminate or reduce dust pollution to the environment — considering their good dust suppression effect, they have been widely used and developed.”
They noted that despite availability, chemical suppressants generally faced problems such as single function and high price, as well as disadvantages such as toxicity, corrosiveness, refractory degradation, secondary pollution, and limited open-air application.