Boral understands that communities close to our quarry sites have questions and concerns regarding possible inhalation exposures to airborne Crystalline Silica.   

What is RCS?   

Crystalline silica is a natural substance found in sand, stone, concrete, and mortar. It is also used to make a variety of products including artificial stone products (such as kitchen and bathroom benchtops), bricks and tiles. When workers process materials containing crystalline silica with power tools or other machinery, airborne dust particles can be generated, a proportion of which may be small enough in size to lodge deep in the respirable region of the lungs and potentially cause serious illnesses or diseases - including silicosis. These dust particles are thus called Respirable Crystalline Silica – or ‘RCS’.

The rock present at Montrose quarry is Rhyodacite and Rhyolite hard rock which is crushed for use in the construction industry as aggregate for end uses such as road bases, concrete, asphalt (asphalt and road-sealing aggregates) and revetment works.

The free silica content of the rock at Montrose is estimated to be about 33% and locked within crystalline rock. Free Silica Content refers to the amount of unbound crystalline silica, typically in the form of quartz, present in a material - especially in dust or soil samples. It’s called “free” because it’s not chemically bonded to other elements or compounds.

It should be noted, however, that the amount of free silica in the source rock is not indicative of the respirable crystalline silica percentage in the dust. The respirable proportion in any dust is largely dependent upon how the rock is processed.

To understand the impacts of the proposal, Boral undertook 12 months of continuous air quality monitoring on the eastern boundary of the quarry, with particular focus on respiratory crystalline silica (RCS).

Using this baseline data, predictions were undertaken for 33 nearby residences to the east and north-east, and the south and south-west of the Quarry. 

The maximum cumulative RCS concentrations were 0.5 µg/m3  at the nearest sensitive receptor (SLR 2024). This is significantly less that the concentration of RCS that an individual can be exposed to for life without significant risk of harm (3 µg/m3). 

The results of the comparison show that the measured and modelled RCS emissions are markedly lower than the RCS concentration associated with no significant risk of harm, thus the risk of silicosis in the population living around Montrose Quarry due to RCS exposure from the Quarry is low

This is consistent with the consensus in the scientific literature that to date, there are no known adverse health effects associated with non-occupational exposure to RCS.