Site: The Store Residential, 854 Hunter Street, Newcastle NSW
Service: Occupational hygiene — personal air monitoring for respirable dust and respirable crystalline silica
Field program: October 2025, five consecutive days
Samples: 15 personal samples across 15 workers, three per day
The brief
BLOC engaged Confluence Environmental to establish a baseline of worker exposure to respirable dust and respirable crystalline silica (RCS) across an active multi-storey residential construction site in Newcastle's West End, with more than 100 workers on site at the time of sampling.
The driver was straightforward. Under the Work Health and Safety Regulation, a PCBU must assess exposure and verify that its controls are adequate wherever there is uncertainty about worker exposure or health risk. BLOC had controls in place — water suppression, on-tool extraction, designated silica work areas, disposable respirators — but no exposure data confirming they were working. Without that data there is no way to demonstrate exposures are as low as reasonably practicable, and no baseline against which to verify future changes in method or materials.
What we did
Monitoring was designed to capture normal production, not a staged demonstration. Sampling ran over five consecutive days across the tasks that generate silica on a build of this type: cutting and grinding brick and masonry, drilling and demolishing concrete, mixing render, grout and concrete, formwork preparation and dismantling, and sweeping.
Personal sampling was undertaken in the breathing zone in accordance with AS 2985:2009, using calibrated SKC conductive plastic cyclones fitted with 25 mm PVC filters at a nominal flow rate of 2.2 L/min, selectively collecting the respirable fraction at or below 10 µm aerodynamic diameter. Flow rates were recorded at commencement and completion against the ±5% stability requirement.
Filters were sealed, documented under chain of custody and submitted to a NATA-accredited laboratory for gravimetric determination, then analysed for crystalline silica content by X-ray diffractometry in accordance with NIOSH 7500. Two field blanks were carried through identical handling without air drawn through them, and returned negligible contamination, verifying both sampling integrity and laboratory performance.
Scope also included a task-specific Safe Work Method Statement, site induction, and consultation with BLOC's WHS representatives to confirm rosters, tasks and control practice before sampling commenced.
Adjusting the exposure standards to the roster
This is where a lot of silica monitoring quietly fails. The Safe Work Australia Workplace Exposure Standards — 3.0 mg/m³ for respirable dust and 0.05 mg/m³ for RCS — are 8-hour time-weighted averages. Site rosters were not 8-hour: some crews worked 10-hour shifts five days on, others 10-hour shifts six days on with a shorter Saturday.
Applying the Québec model, as recommended under Safe Work Australia's guidance on interpreting exposure standards and by the AIOH, we derived project-specific criteria for each roster.
Each worker's result was assessed against the criterion matching their actual roster. Assessing a six-day crew against an 8-hour standard would have understated exposure by close to half.
The outcome
All results complied with the applicable exposure standards, and the controls BLOC had implemented were confirmed as effective for general site conditions.
The dataset gave BLOC a defensible baseline and a clear set of next steps: a site-specific silica risk assessment and control plan built around Similar Exposure Groups, targeted control verification, a formal respiratory protection program compliant with AS/NZS 1715:2009 including fit testing, continued prohibition on compressed-air cleaning and dry sweeping in favour of HEPA vacuuming and wet methods, silica awareness training ahead of the control plan rollout, and follow-up monitoring to verify the controls once implemented.
Monitoring records and any associated health surveillance records must be retained for 30 years and made accessible to affected workers. The baseline established here is the start of that record, not a one-off compliance exercise.
Why this matters
Silicosis is irreversible. Respirable crystalline silica is generated by ordinary construction tasks — cutting brick, drilling concrete, mixing mortar — and the particles that cause harm are invisible. Exposure standards are not thresholds between safe and unsafe; they are the point above which risk becomes unacceptable, and health effects can occur below them.
Confluence Environmental provides occupational hygiene services across NSW and the ACT, including personal exposure monitoring for respirable crystalline silica, dust, welding fume and noise, silica risk assessments and control plans, and respiratory protection program support.