Silica Exposure Limits
Compliance · Compliance overview
Silica exposure limits are the regulatory reference values that personal silica air sampling results are compared against. This page sets out the UK silica WEL for respirable crystalline silica, the silica workplace limits employers commonly track as in-house action levels, and how silica regulations and silica legal limits drive monitoring and control decisions.
The UK silica WEL
The principal silica exposure limit in the UK is the Workplace Exposure Limit for respirable crystalline silica published in HSE EH40. It is an 8-hour time-weighted average (TWA) and applies to the respirable fraction of crystalline silica — the lung-penetrating fraction defined by the respirable convention in BS EN 481 and sampled by cyclone heads on personal pumped equipment.
The silica WEL is the headline reference point for comparison of measured exposures. It is not a safe threshold below which respirable crystalline silica is harmless; it is the regulatory ceiling against which silica exposure is judged for compliance under COSHH. Employers are expected to control silica exposure so far as is reasonably practicable, which in many workplaces means working to in-house action levels below the WEL rather than against the WEL itself.
Respirable crystalline silica limits and in-house action levels
Many UK employers operate in-house action levels for respirable crystalline silica set below the silica WEL — commonly at a fraction of the WEL — to trigger review of water suppression, on-tool extraction or silica LEV before measured exposures approach the legal limit. This is a defensible operational pattern: it gives the silica control system a margin and treats drift as a signal rather than as a failure.
Where measured silica exposure exceeds the in-house action level, the expected response is engineering — reviewing water suppression flow, on-tool capture, silica LEV face velocity, enclosure integrity, work pattern or material substitution — rather than a reflexive RPE upgrade. Where measured silica exposure exceeds the silica WEL, immediate review and remedial action are expected, with the COSHH assessment updated accordingly.
- Silica WEL — 8-hour TWA respirable crystalline silica limit in HSE EH40.
- In-house action level — typically set below the WEL as an early warning.
- Short-term peaks — relevant for high-energy tasks such as breaking and blasting.
- BS EN 689 — strategy for comparing measured silica exposure with the WEL.
Workplace context for silica exposure limits
Silica workplace limits matter most where silica is generated routinely: construction cutting and chasing, engineered stone fabrication, concrete cutting and coring, abrasive blasting, quarrying and tunnelling. In each of these workplaces the silica WEL is the reference value against which personal silica air sampling results are compared and against which the adequacy of silica controls is judged.
Silica regulations also matter in workplaces where silica exposure is intermittent but high — short cuts in maintenance work, occasional demolition, periodic blasting — because short-duration high-energy tasks can dominate an 8-hour TWA even where the rest of the shift is silica-quiet. Task-based sampling is normally added alongside full-shift sampling in those workplaces to characterise the peak rather than dilute it across the day.
Silica monitoring against the WEL — sampling strategy
Comparing measured silica exposure with the silica WEL is done under the strategy in BS EN 689. That means defining similar exposure groups (SEGs) by task, material and controls; sampling sufficient operators within each SEG for the result to support a statistical statement; and interpreting results against the WEL rather than reading a single sample as compliant or non-compliant.
Full-shift personal sampling on the operator's lapel with a respirable cyclone is the standard method. Filters are weighed gravimetrically for respirable dust mass and analysed for crystalline silica content by X-ray diffraction or infrared spectroscopy. Results are time-weighted to an 8-hour reference period and reported per operator, per SEG and against the silica WEL.
Silica legal limits and the wider regulatory frame
Silica legal limits sit within the broader silica regulatory frame: COSHH places the duty on employers to assess, prevent or control silica exposure; HSE EH40 publishes the silica WEL itself; CDM places duties on principal contractors and designers in construction silica work; LOLER and PUWER touch silica-related equipment; and Regulation 9 of COSHH places the thorough examination duty on silica LEV.
The silica WEL is the most visible number in this frame, but it is not the whole compliance picture. A workplace can sit below the silica WEL on measured silica exposure and still fall short of silica COSHH duties on assessment, control, training, surveillance and review. The silica compliance page covers the wider obligations in more detail.
When to request silica monitoring against the WEL
Workplaces commission silica air sampling against the silica WEL when introducing new silica-generating processes, switching materials, changing controls, responding to inspection or enforcement, supporting a tender or insurance requirement, refreshing a COSHH assessment, or simply maintaining a periodic verification cycle for an established silica control system.
It is also commissioned where in-house action levels have been exceeded on previous rounds and the workplace needs measured evidence that the silica control changes since then have brought respirable crystalline silica exposure back to a defensible position against the silica WEL.
Frequently asked questions
What is the silica WEL in the UK?
The silica WEL is the Workplace Exposure Limit for respirable crystalline silica published in HSE EH40, expressed as an 8-hour time-weighted average. It applies to the lung-penetrating respirable fraction of crystalline silica sampled by cyclone heads on personal pumped equipment. The current value should be checked against the latest edition of EH40.
Is sitting below the silica WEL the same as being silica COSHH compliant?
No. Measured silica exposure below the WEL is necessary but not sufficient for silica COSHH compliance. The duties under COSHH also include silica risk assessment, control selection against the hierarchy, silica LEV thorough examination, RPE fit testing, training, health surveillance and periodic review. A workplace can sit below the silica WEL on the air monitoring data and still fall short on those.
What is an in-house action level for silica?
An in-house action level is a self-imposed silica exposure trigger set below the silica WEL, used to flag drift in silica control before measured exposures approach the legal limit. It is a defensible operational pattern and is commonly used in engineered stone fabrication, concrete cutting and quarry processing workplaces.
How is short-term peak silica exposure handled against an 8-hour WEL?
Short, high-energy silica tasks are captured with task-based personal sampling alongside the full-shift sample, so the peak is characterised in its own right rather than diluted across the 8-hour TWA. The full-shift result remains the figure compared against the silica WEL, but the task-based result drives silica control decisions on that specific task.
Do silica exposure limits apply to bystanders and adjacent trades?
Yes. The silica WEL applies to any worker exposed to respirable crystalline silica in the course of work, not only to the operator running the tool. Bystander and adjacent-trade silica exposure is normally characterised through targeted personal sampling on workers whose proximity, task or location places them within the silica exposure envelope.
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