Why is the subject of dust important?
Long-term exposure to high concentrations of dust generated by mining and quarrying activities can cause disabling lung diseases such as silicosis (caused by respirable silica dust).
There are usually years between first exposure to dust and the appearance of symptoms. In some cases, very high exposures to dust may bring on symptoms of disease earlier than previously thought (e.g. silicosis).
People in control of mining operations must keep dust generation to a minimum. As a worker, make sure you understand dust control measures in place at your workplace. This booklet will help you understand the risks and what measures should be in place to minimise exposure to respirable dust, respirable crystalline silica and inhalable dust to as low as reasonably practicable.
What is airborne dust?
Dust suspended in the atmosphere is known as airborne dust. Dust may become airborne for a variety of reasons (e.g. mining activities including blasting, digging and drilling, crushing, driving vehicles over dirt roads and wind).
What is inhalable and respirable dust?
The normal action of breathing can result in the inhalation of dust particles.
Dust particles vary in size and it is the size of the particle that determines its classifcation as either an inhalable or respirable dust. The size of the particle plays an important role in the development of disease. The size of the particle infuences the type and extent of health impacts that can result from exposure.
Inhalable dust
• Particles are less than 0.1 mm in diameter and can be easily seen.
• Particles are breathed in but trapped in the mouth, nose or upper part of the respiratory tract.
Respirable dust
• Particles (non-classifed) are less than 0.005 mm and are invisible to the naked eye.
• Particles are breathed in and retained in the lung and penetrate deep into the lung (alveolar region) where gas exchange takes place.
Respirable dust may be present in visible or inhalable dust, but it may also be present when there is no visible evidence of dust.
Respirable crystalline silica
• Quartz is the most common form of crystalline silica and is the second most common mineral on the earth’s surface. Crystalline forms of silica have been associated with a variety of diseases primarily afecting the lungs.
• Respirable crystalline silica is the respirable dust fraction of crystalline silica.
Dust particle size comparison
Human hair Inhalable dust Respirable dust 89 microns < 100 microns < 5 microns (0.089 mm) (0.1 mm) (0.005 mm)
What are the legislated airborne dust limits?
In NSW, the specifed exposure limits or standards are shown below:
Respirable dust = 3 mg/m3
Respirable crystalline silica = 0.1 mg/m3
Inhalable dust = 10 mg/ m3
The limits above are based on 40 hours a week (8 hours a day, 5 days a week).
Should exposure limits be less for extended shifs?
Yes, if you work more than 40 hours a week the exposure limit is lower. For more information refer to Guidance on the interpretation of workplace exposure standards for airborne contaminants (Safe Work Australia April 2018).
What defence mechanism does your body have against dust?
• Trapping larger sized particles (inhalable dust particles) in the mucus of the upper airways.
• Sneezing or coughing to expel the larger particles.
• Airway constriction as a response to irritation, preventing particles from moving deeper into the lungs.
• Scavenger cells called macrophages in the lungs help dissolve smaller-sized particles (respirable dust particles). These cells dissolve dust particles by surrounding them. If there is too much respirable dust (an overload situation) the scavenger cells cannot completely clear the dust. The respirable dust and respirable crystalline silica that remains over a long period of time can lead to serious health issues (e.g. silicosis).
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