Silica Dust Monitoring
Monitoring · Monitoring overview
Silica dust monitoring is the structured measurement of respirable crystalline silica in the worker’s breathing zone so that employers can compare silica exposure against the silica Workplace Exposure Limit, demonstrate adequacy of silica controls under COSHH, and decide whether water suppression, on-tool extraction, silica LEV and RPE are doing the job they were designed to do.
What silica dust monitoring covers
Silica dust monitoring — also referred to as silica air monitoring, silica dust testing, workplace silica testing and RCS monitoring — is the personal pumped air sampling and laboratory analysis used to quantify respirable crystalline silica exposure across a working shift. It exists to answer two operational questions: is silica exposure being controlled below the WEL, and is the silica control system in place actually working as designed.
A silica monitoring programme typically combines personal silica air sampling for representative operators and tasks, with supporting static sampling for diagnostic work and short-term task-based sampling for high-energy peaks such as breaking, scabbling or short concrete cuts. Together this provides the silica exposure data needed for a credible COSHH review.
Sampling strategy under BS EN 689
Defensible silica monitoring follows the strategy in BS EN 689 for comparison with limit values. That means defining similar exposure groups (SEGs) — operators who share materials, tasks and controls — sampling sufficient operators within each SEG, and interpreting results against the WEL using the EN 689 statistical framework rather than a single sample.
For RCS specifically, an EN 689-aligned programme will normally cover full-shift personal sampling, supplemented by task-based sampling where exposure is dominated by short, intense activities (for example a 30-minute concrete cut within an otherwise low-exposure shift). The goal is a silica exposure profile that fairly represents the work — not a single low result from a quiet day.
- Define similar exposure groups by task, material and controls.
- Sample enough operators per SEG to support EN 689 interpretation.
- Use full-shift personal sampling with cyclone heads for the WEL comparison.
- Add task-based sampling for short, high-energy silica tasks.
- Document RPE use, water suppression and on-tool extraction at each sample point.
Equipment and on-site method
Personal sampling pumps are calibrated against the cyclone before and after the shift at the manufacturer’s specified flow rate (typically 2.2 L/min for SIMPEDS-type heads). The cyclone is clipped to the operator’s lapel within the breathing zone, with the pump worn on the belt. Pre-weighed filters are loaded under clean conditions and field blanks are run alongside the live samples to control for handling effects.
Throughout the shift the field hygienist records task durations, tools, materials, water suppression and on-tool extraction in use, workshop ventilation conditions, RPE worn and any interruptions. Without this context the laboratory number cannot be interpreted defensibly — silica monitoring is as much a documentation exercise as a measurement exercise.
Laboratory analysis and reporting
Filters are returned for gravimetric weighing to determine respirable dust mass, then analysed for crystalline silica content by X-ray diffraction or infrared spectroscopy at a laboratory accredited for the method. Results are time-weighted to an 8-hour reference period and reported per operator and per SEG, with comparison against the silica WEL in HSE EH40 and an EN 689-style statistical commentary where the dataset supports it.
A useful silica monitoring report does not stop at numbers. It links each result back to the specific task, material and control configuration, calls out where in-house action levels were exceeded, and identifies the control changes most likely to reduce silica exposure on the next sampling round.
How silica monitoring feeds the COSHH cycle
Silica monitoring data is one of the primary inputs into the silica COSHH assessment. It informs the assessment of residual silica exposure after controls, supports decisions about whether to escalate from on-tool extraction to enclosure or from RPE to engineering control, evidences the adequacy of silica LEV and feeds into health surveillance scope and frequency.
Where monitoring shows silica exposure above the WEL or above the employer’s in-house action level, the expected response is engineering — reviewing water suppression, on-tool extraction capture, silica LEV face velocity, enclosure integrity, work pattern and material substitution — rather than reflexively upgrading RPE.
When to request silica monitoring services
Workplaces typically commission silica dust monitoring when introducing new silica-generating processes, fabricating engineered stone, scaling up concrete cutting or coring work, changing on-tool extraction or LEV provision, responding to a workplace inspection or enforcement notice, supporting a tender or insurance requirement, or updating a COSHH assessment that has run past its review point.
Periodic silica monitoring is normally appropriate even for stable workplaces: tools wear, extraction capture drifts, materials are switched and operator behaviour changes. Without a refreshed silica exposure profile, a COSHH review is working from assumptions, not evidence.
Frequently asked questions
What is silica dust monitoring measuring exactly?
Silica dust monitoring measures the airborne respirable crystalline silica concentration in the worker’s breathing zone over a representative shift, expressed as an 8-hour time-weighted average and compared with the silica WEL. It is not a measure of total dust or of nuisance dust; it is specifically the lung-penetrating crystalline silica fraction.
How long does a silica monitoring visit take?
A typical silica monitoring visit covers a full working shift per operator sampled, with pump calibration and setup before work begins and post-shift recovery and documentation afterwards. Short task-based silica samples can be much shorter — 15 to 60 minutes — but are normally added alongside a full-shift personal sample rather than instead of it.
Can silica monitoring be done without disrupting production?
Yes. Personal sampling equipment is worn on the lapel and belt and operators continue normal work. The constraint is documentation — the field hygienist needs access to observe tasks, tools, materials and controls. Production typically continues throughout silica air monitoring.
What does a silica monitoring report contain?
A defensible silica monitoring report contains operator-level RCS exposure results time-weighted to 8 hours, comparison against the silica WEL, the sampling strategy used (including SEG definitions where applicable), task and control documentation per sample, an EN 689-style statistical commentary where the dataset supports it, and prioritised silica control recommendations.
Is one round of silica monitoring enough?
Rarely. A single round 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 SEG before drawing firm conclusions about compliance with the silica WEL.
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