Dust is an inevitable part of mining. It’s an unfortunate truth that something so small can cause far-reaching health, safety and environmental impacts. 

In this article, we’ll look at the different types of dust generated by mining operations, specifically Respirable Dust.  We’ll also explore the long-term consequences of breathing in Respirable Dust, relevant legislation in regard to exposure limits, and how mines can implement highly effective control measures for ensuring compliance and reducing worker & community exposure.  

How is dust classified?

From a legislative point of view, dust is considered an Airborne Contaminant and refers to both toxic and non-toxic particles. Dust may be classified into the following categories:

• Inhalable Dust consists of particles less than 100 microns in size and may be visible to the naked eye. This is the fraction of a dust cloud that may be breathed into the nose, mouth or lungs. Inhalable dust particles can affect your upper respiratory system (the nose, mouth, throat or upper respiratory tract).
• Respirable Dust consists of particles smaller than 10 microns. These dust particles are too small to be seen by the naked eye. Their extremely small size also means they can be breathed deep into your lungs and lead to lung damage. 
  
  

Other methods to measure dust involves the term particulate matter or PM – a value used to measure suspended particulate matter. The type and size of PM in the air has impacts on the surrounding environment and on the health of those breathing it in. The World Health Organisation (WHO) identifies two size fractions when classifying dust:

• PM₁₀ dust consists of coarse and fine particles with a diameter 10 microns or less (smaller than 1/7th of a hair width). This is the same size particles as Respirable Dust.
• PM_2.5 are fine particles with a diameter of 2.5 microns or less. These particles are so small they can get deep into the lungs and into the bloodstream. PM₁₀ includes PM_2.5.

Respirable Dust in mining operations 

Around 40% of dust from mining activities consists of Respirable or PM₁₀ dust and is generated from activities such as mechanical disturbance of rock and soil materials by dragline or shovel, bulldozing, blasting and vehicles on haul roads.

PM_2.5 dust (i.e. fine particles) accounts for about 5% of the particles emitted during mining processes. Fine particles produced at mine sites are mainly from vehicle and mobile equipment exhausts.

Health impacts of mine generated Respirable Dust 

Because such a high percentage of dust generated at mine sites is classified as Respirable Dust, it’s a common cause of concern for mine workers and mine operators. Prolonged exposure to Respirable Dust has been proven to have many short- and long-term adverse effects on mine workers and people living in surrounding communities, such as:

Short-term exposure (hours to days) can lead to:

• Irritated eyes, nose and throat
• Worsening asthma and lung diseases such as chronic bronchitis (also called chronic obstructive pulmonary disease or COPD)
• Heart attacks and arrhythmias (irregular heartbeat) in people with heart disease
• Increases in hospital admissions and premature death due to diseases of the respiratory and cardiovascular systems

Long-term exposure (many years) can lead to:

• Reduced lung function
• Development of cardiovascular and respiratory diseases
• Increased rate of disease progression
• Reduction in life expectancy

Aside from impacts from general dust, certain materials pose greater health risks than others. Below are some examples of the most severe types of health conditions as a result of mining different materials.

Environmental and community impacts of mine generated Respirable Dust 

The impact of mining dust on a nearby community depends on the distance from the mine site and climatic conditions such as prevailing wind direction.

Common community concerns about mine site dust often relate to visibility of dust plumes and dust sources. Visible dust is usually due to short-term episodes of high emissions, such as from blasting.

Other community impacts include dust depositing on work surfaces, fabrics (such as washing) or on house roofs, and the transfer of dust from roofs to water tanks, during rain, contaminating stored water. 

In terms of environmental impacts, Respirable Dust particles can be carried over long distances by wind and then settle on ground or in water. The effects of this settling may include:

• Changing the nutrient balance in coastal waters and large river basins
• Depleting the nutrients in soil
• Damaging sensitive forests and farm crops
• Affecting the diversity of ecosystems

What legislation is in place to limit Respirable Dust exposure?

Occupational Exposure Limits (OELs) or workplace exposure limits (WELs) are a key element in dust risk management for mines and are often stipulated in relevant regulations.  Although obvious exposure to known harmful agents should be controlled regardless of any existing regulation, establishment of a control limit often draws attention to a substance. 

OELs are usually expressed in one of the following forms: 

• Time-weighted average concentration (TWA), which is the average concentration over a full shift, usually 8 hours
• Ceiling concentration, which is an instantaneous concentration not to be exceeded at any time
• Short-term exposure limit (STEL), which is the average concentration over a specified time, e.g. 15 minutes

For types of regulated types of dust, such as coal, which have long-term exposure effects, OELs are usually given as TWAs.

Safe Work Australia, as well as state safe work or mining resources regulators, provide guidance around OELs – as a guideline, these are:

^{*Inhalable and respirable dust and particulates not otherwise classified.}

How can Respirable Dust levels be reduced in mine sites?

Dust control measures should include a mixture of preventative engineering controls (such as enclosure of conveyors or correct road construction methods) and suppression measures (such as watering stockpiles, materials in tipping areas and at transfer points, and suppression on roads). 

While using low-pressure water sprayer is a primary dust control measure for many mines in Australia, there are numerous limits to this approach, such as:

• Excessive water pooling and run-off, leading to health and safety risks. 
• Chutes and conveyors becoming clogged. 
• Increased corrosion of conveyors and other infrastructure as water is carried through the entire plant.
• Excessive moisture content building up in the materials that are being watered. 

Perhaps most importantly, low pressure water is not able to sufficiently subdue PM10 sized dust particles.  The more effective approach is the implementation of high pressure dust suppression systems. 

Dust suppression systems are misting systems which use low volumes of water at high pressure (more than 50 bar) to add a fine atomised mist to the air to capture and subdue airborne dust.

Unlike standard spray systems, which use large volumes of water at low-pressure, high-pressure suppression systems are specifically calibrated to capture PM10 dust. 

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 atomised water droplets to collide and agglomerate to airborne dust particles, increasing their mass, and thus allowing them to fall to the ground due to gravity. If the water droplets are too large, the fast-moving airborne dust will simply flow around them. 

High pressure dust suppression systems can reduce levels of PM10 dust by 80%+. This makes dust suppression a highly effective strategy in:

• Reducing the likelihood of workers developing dust related health problems 
• Improving on-site safety
• Improving community and environmental outcomes

Want to learn more about control measures for PM₁₀ dust at your mine site?

As leading providers of dust suppression systems, Dust-A-Side Australia understands that the risks of Respirable Dust can simply not be ignored. To learn more about our custom-built dust suppression systems, call us on + 1800 662 387. Or you can get in touch by clicking here.