Respirable Crystalline Silica
What is Respirable Crystalline Silica ?
Silicon dioxide (SiO2) is one of the most abundant compounds in the earth’s crust which is found as rocks sand and soil. While there are many forms of silicon dioxide, crystalline forms which have an arranged molecular structure can pose a serious health hazard if the particles lodge within the inner lining of the lung. It is this form of silicon dioxide known as Respirable Crystalline Silica (RCS), Respirable Crystlline Quartz (RCQ).
Where is Respirable Crystalline Silica found ?
Respirable Crystalline Silica is generally found as a fugitive dust during mining, construction and excavation. It is also used in manufacturing to make glass, ceramics, electrical components and refractory linings.
Health effects of Respirable Crystalline Silica
Large dust particles of crystalline silica will be coughed up, exhaled or brought up through the mucociliary elevator; however particles which are much smaller, less than 16 microns will be able to reach the inner lining of the lungs. This may in term affect the gas exchange system of lungs, leading to reduced lung function.
Increased exposures of respirable crystalline silica may lead to pneumoconiosis, Chronic Obstructive Pulmonary Disease (COPD) and scarring of the lungs (fibrosis known as silicosis). This will generally show up in a radiograph (x-ray generally indicating pleural plaques, being an inflammatory reaction to the particles trapped in the lung.
It has also been confirmed that Respirable Crystalline Silica may also lead to increased risk of lung cancer at relatively high exposures.
Air monitoring and testing for Respirable Crystalline Silica
Air monitoring and testing is conducted to:
AS 2985 Workplace atmospheres – Method for sampling and gravimetric determination of respirable dust
An air monitoring pump draws air through a cyclone sampling head which effectively disregards dust particles greater than 16 microns. The particles less than 16 microns are known as the respirable fraction and are then collected on a filter paper which is weighed and analysed. The percentage of crystalline silica is then determined using FTIR or X-ray diffraction to compare against the exposure standard.
The air monitoring and dust testing can determine the airborne concentration of respirable crystalline silica at static locations to assess the fugitive emissions or placed on people to determine the likely exposures during the working shift.
The effectiveness of control strategies can be determined by air monitoring the respirable crystalline silica exposures before and after implementation. Also the air monitoring and sampling strategy requires consideration of Similar Exposure Groups (SEGS). For instance, people working in the office will have difference exposures to people working at the quarry face.
Australian Exposure Standard (ES) for Respirable Crystalline Silica?
The Australian occupational exposure standards for Respirable Crystalline Silica as Cristobalite, Quartz and Tridymite are set at 0.1 mg/m3 as a time weighted average for an 8 hour day, 5 days a week. This information can be found on the Safe Work Australia Hazardous Substances Information System (HSIS).
The exposure standards are based on epidemiological and toxicological data, however there will always be some interpersonal variability which is why health monitoring for people at increased risk is critical.
Health monitoring for Respirable Crystalline Silica Exposure
Health monitoring using spirometry testing is important for people at high risk as it can detect loss in lung function before significant changes are detected by radiography. The results of spirometry testing can then assist to eliminate the worker from the source of respirable crystalline silica exposure, before significant lung function is lost.