Silica FAQ
Resources · Resources overview
Frequently asked questions on respirable crystalline silica, silica dust monitoring, silica air sampling, silica risk assessment, industry and task silica exposure, and silica controls, silica LEV and silica compliance for UK workplaces. Grouped so H&S managers, occupational hygienists, fabrication supervisors and compliance teams can find the silica answer they need quickly.
How this silica FAQ is organised
The questions below are grouped into six clusters: respirable crystalline silica as a substance, silica dust monitoring, silica air sampling, silica risk assessment, industry and task silica exposure, and silica controls, silica LEV and silica compliance. Each answer is written as standalone reference content scoped strictly to silica exposure in UK workplaces.
Where a question touches a topic that has a dedicated guide on this site - for example the silica WEL, silica LEV thorough examination, or engineered stone dust - the answer points to that guide rather than duplicating the full reference. This silica FAQ is meant to be a quick-answer index, not a replacement for the deeper silica pages.
What this silica FAQ does not cover
This FAQ focuses only on respirable crystalline silica and workplace silica exposure topics. Questions outside silica - covering other workplace contaminants, other regulated substances or general occupational hygiene topics not specific to respirable crystalline silica - are deliberately not answered here and fall outside the editorial scope of silicaexposure.co.uk.
Where a question crosses silica into adjacent regulatory areas (for example general COSHH duties beyond silica, or HSE enforcement in non-silica contexts), the answer stays scoped to silica and points the reader to HSE guidance for the wider picture.
Use these answers alongside the deeper silica guides
Each cluster below pairs with a deeper silica reference page. Use the FAQ for quick orientation; use the underlying silica guide when designing a silica monitoring programme, completing a silica risk assessment or defending a silica compliance position.
Frequently asked questions
RCS - what is respirable crystalline silica?
Respirable crystalline silica is the fine, lung-penetrating fraction of crystalline silica dust released when quartz-bearing materials such as concrete, brick, stone, mortar and engineered stone are cut, ground, drilled, broken, blasted or polished. It is the size fraction sampled by respirable cyclone heads and compared with the silica Workplace Exposure Limit in HSE EH40.
RCS - how does respirable crystalline silica differ from general silica dust?
General silica dust includes coarse particles too large to reach the deep lung. Respirable crystalline silica is the sub-fraction (broadly below about 10 microns aerodynamic diameter, peaking around 4 microns) that penetrates to the alveolar region. RCS is the regulated fraction; bulk silica dust is the operational source of RCS.
RCS - which UK materials are dominant sources of respirable crystalline silica?
Concrete, brick, mortar, sandstone, granite, slate, kerbstone, tile and engineered stone are the dominant sources of respirable crystalline silica in UK workplaces. Engineered stone in particular can sit at or above 90% crystalline silica content, which is why engineered stone dust is treated as a distinct silica exposure scenario.
Silica dust monitoring - what does it actually measure?
Silica dust monitoring measures respirable crystalline silica concentration in the worker's breathing zone using personal pumped sampling and a respirable cyclone, time-weighted to 8 hours and compared with the silica WEL in HSE EH40. It is not a measure of total dust or nuisance dust.
Silica dust monitoring - how long is a typical monitoring visit?
A typical silica dust monitoring visit covers a full working shift per operator sampled, with pump calibration before and after the shift. Short task-based silica samples can be much shorter but are normally added alongside, not instead of, full-shift personal sampling.
Silica dust monitoring - is one round enough?
Rarely. A single round of silica dust monitoring establishes a baseline; periodic re-monitoring is what shows whether silica controls are still effective as tools, materials and operators change. EN 689 interpretation also expects more than one result per similar exposure group.
Silica air sampling - what method is used in the UK?
UK silica air sampling uses personal pumped sampling on the breathing-zone lapel with a respirable cyclone (typically SIMPEDS / Higgins-Dewell type) at the manufacturer-specified flow rate. Filters are gravimetrically weighed for respirable dust mass and analysed for crystalline silica content by X-ray diffraction or FTIR.
Silica air sampling - personal or static sampling?
Personal pumped silica air sampling is the method used to evidence silica exposure against the WEL. Static (area) sampling has a role for characterising background and hot spots but does not replace personal sampling for compliance with the silica Workplace Exposure Limit.
Silica air sampling - what standard is used for interpretation?
BS EN 689 is the standard strategy used to interpret silica air sampling results against the silica WEL, using similar exposure groups and a statistical framework for comparison with limit values rather than relying on a single sample.
Silica risk assessment - what should it cover?
A silica risk assessment under COSHH should identify the silica-generating tasks and materials, characterise current silica exposure (ideally with measured silica monitoring data), evaluate the adequacy of silica controls against the COSHH hierarchy, set RPE requirements based on residual silica exposure, and define the silica monitoring and health surveillance regime.
Silica risk assessment - how often should it be reviewed?
A silica risk assessment should be reviewed whenever tasks, materials or silica controls change in a way that could plausibly alter silica exposure, whenever silica monitoring or health surveillance findings suggest exposure has changed, and otherwise at a periodic interval proportionate to the silica workplace risk.
Silica risk assessment - is silica monitoring data required first?
In most cases yes. A silica risk assessment that judges adequacy of controls without measured silica exposure data is making assumptions. Personal silica air sampling for representative operators and tasks is usually the practical way to anchor the silica exposure profile against the silica WEL.
Industry exposure - why is engineered stone treated as a higher-risk silica scenario?
Engineered stone typically has much higher crystalline silica content than natural stone, often above 90% by mass, and the fabrication tasks (sizing, mitring, edge profiling, polishing) generate intense respirable silica exposure. Wet processing, dedicated silica LEV and robust RPE are normally required to keep silica exposure below the silica WEL.
Industry exposure - what tasks dominate construction silica exposure?
On UK construction sites, respirable crystalline silica exposure is dominated by dry cutting and chasing of concrete, brick and mortar; cutting and coring reinforced concrete; tuck-pointing; breaking and scabbling slabs; and dry sweeping of dust that already contains respirable silica.
Industry exposure - is abrasive blasting always a silica problem?
Abrasive blasting is always a high-energy silica risk where the substrate is silica-bearing, even when substitute blasting media is used, because the substrate itself releases respirable crystalline silica. Enclosure, blast booth ventilation and air-fed RPE are normally required.
Industry exposure - how is quarry silica exposure typically controlled?
Quarry silica exposure is normally controlled through a mix of dust suppression at drilling, crushing, screening and tipping points, cabin pressurisation and filtration for plant operators, and silica-specific RPE for crews working outside protected cabins. Silica monitoring per role evidences whether each control element is doing the job.
Silica controls - what is the COSHH hierarchy for silica?
The COSHH hierarchy applied to silica is: eliminate or substitute the silica source where reasonably practicable, then engineering controls (water suppression, on-tool extraction, enclosure, dedicated silica LEV), then administrative controls and work organisation, then RPE as a complement to engineering control or for short-duration residual silica peaks.
Silica LEV - what is silica-specific about silica LEV systems?
Silica LEV systems are designed for the respirable fraction of silica dust, with capture velocity and hood geometry chosen to control RCS at the point of generation, ducting and filtration sized for the silica dust load, and statutory thorough examination under Regulation 9 of COSHH against the silica-specific control standard.
Silica compliance - what is the silica WEL in the UK?
The silica Workplace Exposure Limit for respirable crystalline silica is the 8-hour TWA value published in HSE EH40. Silica air sampling results are time-weighted to 8 hours and compared against it. The current value should always be read from the latest EH40 edition and is covered on the silica exposure limits guide.
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