Engineered stone and other high-risk silica work

Some silica tasks produce far higher exposures than others, either because the material contains a lot of silica, because the process generates large amounts of fine dust, or because it happens in confined or poorly ventilated spaces. This lesson looks closely at engineered stone fabrication, which has caused an international outbreak of severe silicosis in young workers, and then at other high-risk work: tuckpointing, abrasive blasting, concrete floor grinding, tunnelling and underground work, hydraulic fracturing and foundry work. For each it describes why exposure is high and what controls are expected.

What engineered stone is

Engineered stone, sold under names such as quartz surfacing or artificial stone, is made by binding crushed quartz or other silica with resin and pigments, then pressing and curing it into slabs. It became very popular for kitchen and bathroom countertops from the early 2000s because it is hard, non-porous and available in many colours. Its crystalline silica content is often above 90 per cent, compared with roughly 10 to 45 per cent for natural granite and under 5 per cent for marble.

When engineered stone is cut, edged, polished or drilled, it releases dust that is very rich in respirable crystalline silica. Some research also suggests the dust particles may be especially harmful because of their size, freshly fractured surfaces and the resin and metal additives, although the main driver is the high silica content.

The outbreak

Clusters of accelerated and acute silicosis among engineered stone workers were reported first in Israel and Spain and then in Australia, the United States and elsewhere. Many patients were in their 20s to 40s, some had worked in the trade for less than ten years, and a significant number needed lung transplants or died. The disease was often found late because the workers were young and the illness was not expected.

Whether to ban engineered stone or control it tightly is debated. Supporters of bans argue that small fabrication shops cannot reliably maintain the very high level of control needed and that lower-silica alternatives exist. Opponents argue that well-controlled shops can work safely, that bans shift work to other high-silica materials, and that enforcement of existing limits is the real problem. Both sides agree that dry cutting and polishing of engineered stone is unacceptable.

Why exposure is so high

The key reason is simple arithmetic: for the same amount of respirable dust in the air, a material with three times the silica content produces about three times the silica exposure.

# Same respirable dust concentration, different materials (illustrative).
respirable_dust = 0.5    # mg/m3 of respirable dust during an edging task

materials = {
    "marble (3% silica)": 0.03,
    "granite (30% silica)": 0.30,
    "engineered stone (90% silica)": 0.90,
}
limits = {"ACGIH TLV / most provinces": 0.025, "OSHA PEL": 0.050}

for name, frac in materials.items():
    rcs = respirable_dust * frac
    ratios = ", ".join(f"{rcs/lim:4.1f}x {lab}" for lab, lim in limits.items())
    print(f"{name:30s} {rcs*1000:6.0f} ug/m3  ({ratios})")

marble (3% silica)                 15 ug/m3  ( 0.6x ACGIH TLV / most provinces,  0.3x OSHA PEL)
granite (30% silica)              150 ug/m3  ( 6.0x ACGIH TLV / most provinces,  3.0x OSHA PEL)
engineered stone (90% silica)     450 ug/m3  (18.0x ACGIH TLV / most provinces,  9.0x OSHA PEL)

Fabrication shops add to the problem. Work is often done in small, enclosed spaces with several workers near each other, using hand-held grinders and polishers at high speed. Many shops are small businesses with little access to occupational hygiene support. Installation crews may also cut and adjust slabs on site in kitchens without controls.

Controls for engineered stone fabrication

Because exposures can be so high, engineered stone requires the full set of controls, rigorously maintained:

In Canada, regulators expect these controls under the general silica requirements, and WorkSafeBC and Ontario worker health organizations have published specific guidance for stone fabricators.

Tuckpointing and mortar removal

Tuckpointing, grinding out old mortar joints before repointing, is one of the highest-exposure construction tasks. Mortar can contain a lot of silica, the grinder throws dust directly toward the worker's face, and work is often done at height on scaffolds where the worker cannot step away. Uncontrolled exposures many times the limit have been measured. Lesson 5 worked through the control set: shrouded grinders with properly sized vacuums, respirators even with controls, access restrictions and HEPA clean-up.

Abrasive blasting

Blasting with silica sand to clean or prepare surfaces generated some of the worst historical silicosis outbreaks, including acute silicosis. The sand fractures on impact into fine, freshly broken respirable particles, and the coating being removed may add other hazards, such as lead. Many jurisdictions now restrict or prohibit silica sand for blasting or require alternative abrasives. Where blasting is unavoidable, it should be done in an enclosed blast room or cabinet with ventilation, and blasters need supplied-air blasting helmets. Workers nearby must also be protected.

Concrete floor grinding and polishing

Grinding and polishing concrete floors is common in commercial, warehouse and residential work. Walk-behind and ride-on grinders abrade large areas of silica-rich concrete. Wet grinding or dry grinding with an integrated, high-capacity dust collection system with a HEPA filter is essential. Dry grinding without collection, or using a collector that is too small or poorly maintained, produces very high exposures for the operator and anyone else in the building.

Tunnelling, mining and underground work

Drilling, blasting, mucking and shotcreting in tunnels and mines can produce high silica exposures in confined spaces where ventilation is the main control. Controls include wet drilling, water sprays at transfer points, enclosed and filtered cabs on equipment, adequate ventilation airflow designed by a specialist, and good scheduling so that workers are not in the dust plume after blasting. Mining is often regulated under separate mining regulations, such as MSHA rules in the United States and mining-specific provincial regulations in Canada.

Hydraulic fracturing

Hydraulic fracturing uses large quantities of silica sand, called frac sand, pumped into wells to hold fractures open. Moving the sand with pneumatic transfer, conveyors and sand movers at the well site releases respirable dust. NIOSH field studies in the early 2010s found that a large share of samples at well sites exceeded the silica limits, prompting controls such as enclosed transfer systems, dust collection on sand movers, closing fill ports, reducing drop heights and using alternative proppants where practical.

Foundries

Foundries use silica sand for moulds and cores. Shake-out, where castings are knocked out of sand moulds, and fettling and cleaning castings with grinders and blasting are high-exposure tasks. Heating can convert some quartz to cristobalite. Controls include enclosed and ventilated shake-out stations, local exhaust on grinding benches, mechanized handling, substitute mould materials where feasible and good housekeeping.

Demolition and renovation

Demolition of concrete and masonry structures can release large quantities of silica dust, especially with breakers, crushers and saws. Water sprays and misting cannons, enclosed cabs and keeping workers away from the active zone are the main controls. Renovation adds another complication: older buildings may contain lead paint and asbestos alongside silica, so a pre-work hazard assessment must look for all three. Lessons 7 to 10 cover lead, and HSE-246 covers asbestos.