The following information should be considered when determining how to manage respirable crystalline silica (RCS) exposures in the workplace.
Silica or silicon dioxide (SiO2) is a very common mineral. It occurs in many products including sandstone, concrete, brick and engineered / manufactured stone. Silica is also known as quartz, tripoli and cristobalite.
Crystalline silica is harmful when respirable-sized dust of less than 10 microns is breathed deep into the lungs, as this can cause lung scarring known as silicosis. The fibrosis of the lungs and the associated inflammation may lead to lung cancer.
There is evidence that fresh cut silica particles, with active surfaces, may be more harmful than aged surface modified (less active) particles.
Studies show that people who have RCS exposure greater than 0.065mg/m3 over their working life have an increased risk of lung cancer. At a lifetime average exposure of 0.06mg/m3, the risk of silicosis is estimated at 7%.
The current Australian workplace exposure standard (WES) is 0.1 mg/m3 for an 8-hour working day over a 40-year working life. However medical health monitoring is suggested for ongoing exposures of 0.05mg/m3 RCS over 8 hours.
Safe Work Australia is inviting comment on their review of the Workplace Exposure Standards for airborne contaminants.
The potential for high RCS exposures exists in the following industry sectors.
Manufacturing stone items can cause a dust exposure risk. However the use of engineered or composite stone materials, such as Caesarstone and Silestone, for benchtops in both domestic and commercial premises has increased markedly in the last 10-15 years.
This change in product usage is likely to have increased quartz dust exposure for workers fabricating benchtops by cutting, drilling or polishing.
Whereas natural stone products like granite may contain up to 40% crystalline silica (quartz) by weight, the engineered products may have 93% or higher quartz content.
Mining, quarrying, tunnelling and extractive minerals
Exposure to RCS is a known issue, with risks especially during rock crushing activities. Silicosis prevention in South Australia is assisted by the Mining and Quarrying OHS Committee.
Construction, building and demolition
Fine silica dust can be formed on sites from concrete cutting and using dust generating tools on stone.
As a Person Conducting a Business or Undertaking (PCBU) you must determine if an RCS dust exposure risk exists at your workplace. This can be done by measuring the workplace or reviewing data, such as for tool extraction systems etc.
Control for RCS dust exposure must be put in place if the exposure can’t be eliminated.
The work health and safety (WHS) hierarchy of risk control, ranked from the highest level of protection and reliability to the lowest, suggests the following controls:
Engineering controls – dust suppression
- apply water suppression systems to reduce dust generation.
Engineering controls – dust extraction /LEV
- use local exhaust ventilation (LEV) systems to remove dust at the source
- ensure LEV is correctly placed and operates at effective flow rates
- use dust removal systems on tools to reduce dust exposure of mobile workers.
Engineering controls – isolation / containment
- isolate areas of the workplace where dust is generated by other workers
- exhaust and filter air from the isolated area.
- ensure regular housekeeping to prevent the accumulation of dust
- restrict time of exposure / use worker rotation.
Personal protective equipment
- provide personal protective equipment (PPE) that is suitable for the nature of the work and the hazard, is comfortable to wear and of a suitable size and fit, is maintained / repaired / replaced when needed, and is used or worn by workers trained in its use and care
- assess levels of personal exposure among workers performing high risk tasks.
You must provide suitable information, training, instruction and supervision to workers in the use, storage and handling of hazardous chemicals, taking into account the nature of the work, the associated risks and any control measures implemented.
You must also review and revise your control measures, as necessary, to maintain a safe work environment that is without risk to health or safety, so far as is reasonably practicable. This may include both worksite, via an occupational hygienist, and external health monitoring.
If health monitoring is undertaken, records must be kept for 30 years. Health monitoring must be undertaken by a registered medical practitioner, such as thoracic society registered, familiar with the national requirements for silica health monitoring.
Case study: Stonemason
A stonemason had been regularly working with natural marble and granite products for many years, the granite composed of 25% silica.
An occupational hygienist had been engaged to measure the worker’s exposure levels in the early days of setting up the business, and he had regular health monitoring, including an x-ray every 5 years.
Extraction ventilation systems had kept exposures at a level under the WES.
Due to industry demand the business model changed to using engineered stone products which contained more than 90% silica. When the silica exposure levels where rechecked, the RCS levels were above the WES and control systems needed to be modified to bring exposure back under control.
In the interim a system of wearing a powered air purifying respirator was introduced. Once the workshop had implemented wet processes with modified extraction, the respiratory protection used was reduced to a P2 disposable respirator which requires less maintenance
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Crystalline silica and silicosis: Safe Work Australia
Silica and the lung: Workplace Health and Safety Queensland
Silica - Identifying and managing crystalline silica dust exposure: Workplace Health and Safety Queensland
Silica - Technical guide to managing exposure in the workplace: Workplace Health and Safety Queensland
South Australian Mining and Quarrying OHS Committee: Preventing occupational dust diseases
NSW Planning & Environment: Overview of health management including health monitoring and control plans
Business Queensland: Controlling the risk of dust exposure to workers in mines
Business Queensland, mine safety bulletin: Management of dust containing crystalline silica (quartz)