2.2 Reasons to control emissions

The impacts of air emissions depend on the types of pollutants, their release characteristics and the nature of the receiving environment. The intrinsic hazards associated with each pollutant, such as particulate matter, lead or sulphur dioxide, are well documented (substance fact sheets are available through the National Pollutant Inventory at www.npi.gov.au).

Particulate and various gaseous emissions need to be controlled because they may be harmful to personal health or the health of fauna and flora in the environment, cause concern for local communities, become a hazard to safe operations or, in the case of dust, cause increased wear to moving machinery. Dust and odour can cause annoyance and lead to complaints.

Air quality is influenced by the concentrations of a vast number of substances that may be present, some naturally occurring and others due to human activity.

Pollutants emitted from mining and related activities constitute both gases and primary particles (such as dust). Secondary particles are formed in the atmosphere due to reactions involving non-particle primary pollutants: the in-plume formation of sulphate particles from emissions of sulphur dioxide is an example. In the context of this handbook, secondary particles are not of significant concern.

Dust derived from the mechanical breakdown of rocks and soil is the most widespread and abundant emission from mines, and occurs across a wide range of particle sizes. Total suspended particulate matter (TSP) refers to the full size spectrum of suspended dust particles. Of more direct relevance to health are the finer fractions, PM10 (particles less than 10 microns in diameter) and, especially, PM2.5 (less than 2.5 microns). Finer particles are more readily transported into the lungs where they can become lodged and cause irritation and disease.

While particle size is the main focus of regulatory standards, the potential for particles to damage health is also influenced by their chemistry and shape, and research into detailing these aspects continues. In the case of earth dusts, mineralogy is a key. Depending on the rocks being mined and handled, dust may contain significant amounts of hazardous substances such as lead and other heavy metals, crystalline silica, asbestos or radio nuclides, which adversely affect health at very low exposure levels. Hence, it is important to understand the characteristics of emitted particles to ensure that especially hazardous components are properly controlled.

In general, smaller particles are carried further by the wind than larger particles. Particles that are finer than 10 microns can be carried around the world; they provide the hazy mornings and evenings that we often see when there has

been strong wind. Wind strength, particle size, moisture, porosity and density all play a role in the distance that a particle will be carried from the source. Local communities can be affected by the nuisance effect of particulate emissions through dust deposition on sensitive surfaces such as washing, furniture and cars. Safety on and off site can be adversely affected by dust clouds that limit visibility, increasing the risk of motor vehicle accidents.

Dust increases maintenance costs as it gets in between moving parts of machinery. For example, dust ingress into bearings causes the oil and dust to mix to form a highly efficient grinding paste which can quickly destroy the usefulness of that bearing. Fan impellers are impacted and worn away at the tips by larger (greater than 30 microns) particles of dust. In order to manage dustiness, the material characteristics must be analysed to provide the information that leads to a solution. The particle characteristics that must be understood include the mineralogy, particle size distribution, moisture, porosity, density and, in some cases, the particle charge.

Gaseous emissions arising from fuel combustion (for example, power generation) or mineral processing (for example, ore roasting or smelting) include pollutants such as sulphur dioxide and nitrogen dioxide which have well-defined human health effects and are tightly regulated in the ambient environment and workplace. Odour emissions can arise from some mining and related processes, such as oil shale processing, and gold ore roasting or leaching.

The occurrence of annoying odours, especially on a regular basis, can cause concern in a community. In the same way, nuisance dust can lead to complaints. Complaints are normally a symptom of severe annoyance, but an absence of complaints does not necessarily mean the absence of a problem: there can be complex drivers behind a person’s decision to lodge or not lodge a complaint.

Complaints can lead to regulatory intervention and potentially expensive programs to deal with complaints management and process rectification.

If odour or dust problems do occur, it is important that each complaint is properly investigated and followed up with the complainant and regulator, and is fully documented. A pattern of complaints may point to specific process or weather conditions, informing the design of a reactive management program which avoids certain activities during the identified adverse conditions.

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