Health monitoring: Silica (respirable crystalline)

In January 2021, legislation was passed for low dose high resolution computed tomography (HRCT) scan of the chest to replace chest X-ray in Western Australia as the radiological screening test for occupational exposure to silica. This means that chest X-rays are no longer used for this purpose.

The Work Health and Safety (General) Regulations 2022, Schedule 14 – Requirements for health monitoring, states that the type of health monitoring required for crystalline silica is:

“Low dose high resolution computed tomography of the chest at less than 1 millisievert (mSv) equivalent dose for the entire study. The study must image the whole of each lung on inspiration at 1.5 mm slice thickness or less, without an interslice gap, and must include expiratory imaging. The images must be of adequate quality to detect subtle abnormalities, including ground glass opacities and small nodules.”

Note: Supine views only; prone views are not required. No contrast should be used.

Kitchen/bathroom benchtop fabricators and installers are exposed to hazardous silica dust from cutting, drilling, and polishing engineered stone (also known as artificial stone). Compared to the much harder granite (natural stone), engineered stone is relatively easy to fabricate, and far less training and skills are required.

Construction workers cutting, drilling into concrete and resurfacing and polishing are at risk. Quarry workers, mineworkers and tunnellers work in dusty environments where silica dust is released from drilling, blasting, crushing and cutting into natural rock.

Engineered stone, is a composite material made up of silica (80–95%) held in a matrix with polymeric resin. The silica content in natural stone varies from 5% for marble, 20–40% for slate, 25–60% for granite and 70–90% for sandstone.

This is an occupational lung disease caused by the inhalation of respirable crystalline silica. Silicosis is a progressive disease which can remain asymptomatic for decades. There is no effective treatment even after cessation of exposure.

Silica exposure has historically been associated with chronic silicosis in mineworkers and stoneworkers from exposure to relatively low levels of silica dust. Chronic silicosis develops slowly over decades (10–30 years), becoming symptomatic late in life (60s or 70s). A small proportion may develop progressive massive fibrosis (PMF) and respiratory impairment.

The use of engineered stone products for kitchen and bathroom benchtops has been associated with accelerated silicosis in younger workers (30s, 40s and 50s) within 5–10 years of exposure. There is rapid progression with early onset of progressive massive fibrosis, respiratory failure and death. Freshly fractured silica dust from engineered stone is postulated to be more reactive.

Acute silicosis, also known as silico-proteinosis, is rare. This is an acute illness that can occur after exposure to very high concentrations of silica dust. Lipid and proteinaceous material fill the alveoli, resulting in severe symptoms within a few weeks to a few years of initial exposure. Clinically, there is progressive breathlessness, pleuritic chest pain, fever, cough, fatigue, weight loss, and rapid progression to death from respiratory failure.

Respirable crystalline silica particles (5 μm or less) penetrate deep into the alveoli within the lungs. The particles are ingested by macrophages. This results in proliferation of concentric fibrous tissue (often hyaline) surrounding bi-refringent silica particles, and the formation of tiny silicotic nodules. Fibrosis may progress to obliterate the lumen of respiratory bronchioles and pulmonary blood vessels. These nodules concentrate subpleurally, and may coalesce to form larger nodules and masses. Silica is carried to the hilar and mediastinal lymph nodes which may become enlarged and calcified over time.

Silicosis is associated with increased risk of:

• chronic bronchitis
• tuberculosis
• rheumatic disorders (rheumatoid arthritis, systemic lupus erythematosus)
• sarcoidosis
• lung cancer (silica is a Group 1 carcinogen in humans as classified by the International Agency for Research on Cancer).

Early identification enables early and effective management and treatment. Work exposure, symptoms examination and investigative findings must all be considered.

Health monitoring consists of:

• a work exposure history and medical history with an emphasis on respiratory disorders, autoimmune disorders, and potential for lung cancer
• examination of the lungs and rheumatological disorders
• spirometry, and
• low dose HRCT chest scan (where indicated).

An initial health monitoring is recommended followed by annual health assessments with health counselling. Frequency of imaging is outlined below.

The worker must be provided with a copy of the health monitoring report including spirometry and CT report. The worker should take their health monitoring records to their next health monitoring appointment. Portability of health monitoring is important for continuity and to prevent overly frequent screening when changing employment or RMP.

Spirometry should be performed by trained personnel using a spirometer that is calibrated and maintained in line with TSANZ or ATS guidelines. Requirements include:

• at least 3 acceptable manoeuvres
• two largest FVC values are within 0.15 L of each other
• two largest FEV1 values are within 0.15 L of each other.

Spirometry print-outs, including flow-volume graphs, must be available for submission to DMIRS with the health monitoring notification form.

Chest X-rays are no longer required as they are not sensitive enough to detect silicosis nor associated early changes. A full dose diagnostic HRCT chest scan (2–5 mSv) is not suitable as an occupational screening test due to the higher radiation dose.

A low dose HRCT chest scan with a dose limit of 1mSv or less is the legislated screening test. This provides an image quality sufficient to detect silicosis and early changes. No contrast should be used. It is important that radiation exposures are kept as low as possible.

The HRCT scan must be read by a radiologist with expertise in reading such scans. In addition to the standard report on the scan, the modified Kusaka ICOERD classification should be included. The dose length product (DLP) for the scan must be included in the report. The conversion factor for DLP to mSv for chest CT scan is 0.014.

If this service is not available in your regional area, there is scope for the worker to undertake screening in a facility that has this capability within 3–6 months of the date of referral. A full dose HRCT or chest X-ray should not be used as a screening test.

A low dose HRCT chest scan is to be repeated at 2 to 5 yearly intervals depending on the specified Category. However, new workers with no prior significant silica dust or other hazardous dust exposures are not required to have a CT scan at entry.

Engineered stone workers have a higher risk of silicosis. Inadequate dust controls and respiratory protection prior to 2020, were associated with silicosis in engineered stone workers after relatively short periods of intense exposures in younger working age groups.

Health monitoring requirements:

• Annual health monitoring and spirometry.
• All workers with significant silica dust work exposure of 2 years or more will require a 2-yearly low dose HRCT chest scan.
• Workers new to the industry require baseline health monitoring and spirometry testing. A low dose HRCT chest scan is not required unless there is a history of prior significant silica or mixed dust exposure for 2 years or more, or is clinically indicated (RMP decision).
• Workers leaving the industry must have health monitoring and an exit low dose HRCT chest scan, unless the previous health monitoring and CT were within the last 2 years.

This category includes workers who are exposed to silica dusts in all other industries such as stonemasonry (natural stone), construction industry (e.g. concrete cutting, shotcreting, tunnelling, demolition), foundry work, abrasive blasting, fire assay lab (ore sample crushing), quarrying and mining.

Health monitoring requirements:

• Annual health monitoring and spirometry.
• All workers with significant silica dust work exposure of 5 years or more will require a 5-yearly low dose HRCT chest scan.
• Workers new to the industry require a baseline health monitoring and spirometry. A low dose HRCT chest scan is not required unless there is a history of prior significant silica or mixed dust exposure for 5 years or more, or is clinically indicated (RMP decision).
• Workers leaving the industry must have health monitoring and an exit low dose HRCT chest scan, unless the previous health monitoring and CT were within the last 2 years.

Table 1 Health monitoring summary

The RMP’s role is defined by health monitoring requirements including communications with the worker, the PCBU and the regulator for the health and safety of the worker.

• Use WorkSafe’s Silica – Health monitoring report to provide as much information as possible to enable a comprehensive risk assessment of the worker.
• Determine whether the worker may continue to work with silica dust.
• Remove workers with confirmed silicosis from silica work.
• Determine whether referral to a respiratory physician is necessary:
  • to confirm the diagnosis of silicosis \
  • to clarify the significance and work-relatedness of other CT abnormalities.
• In complex cases, take advice from the respiratory physician.

• Inform the worker of the RMP’s requirement to notify and provide results to WorkSafe.
• Inform and explain results of health monitoring to the worker.
• Counsel the worker to stop smoking.
• Encourage good hygiene practices (wash/shower before eating or going home).
• Reinforce safe work practices including consistent use of respiratory protective equipment (RPE) and being clean shaven.
• Enquire into existing controls in the workplace for dust suppression (including wet work)
• If removal from silica work is required, inform the worker (and PCBU)
• Non-work related findings (spirometry or CT) requiring attention are to be forwarded to the worker and their GP to address.

• Provide the PCBU with health monitoring outcome and any recommendations for remedial action to improve safety and health in the workplace.
• Inform the PCBU when referral to a respiratory physician is indicated.
• The PCBU is responsible for the cost of the initial respiratory physician assessment and report where the lung condition is considered likely to be silica-related from current work exposures.
• Inform the PCBU when removal of worker is required.
• The PCBU should consider availability of alternative work that does not expose the worker further to silica dust.

Note: The role of the RMP is limited to health monitoring within the provisions of the WHS legislation. Similarly, the initial role of the respiratory physician is limited to assisting to clarify the diagnosis and significance of chest CT abnormalities. When a work-related lung disease has been confirmed, it is recommended that the worker take advice from their treating medical practitioners and specialists in relation to workers’ compensation. WorkCover is the authority administering the Workers’ Compensation and Injury Management legislation.

• All health monitoring results are to be notified to the regulator on the Silica – Health monitoring report.
• Silicosis cases are to be reported by the RMP promptly to the regulator.
• Email the completed health monitoring questionnaire/notification form, spirometry print-out and CT report to safety@demirs.wa.gov.au
• Forward the respiratory physician report when available.

Note: Incomplete forms will be returned by WorkSafe.