HSE's workplace exposure limit (WEL) for respirable crystalline silica (RCS) is 0.1 mg/m3 averaged over 8 hours -- and dry sweeping or brushing construction dust can spike exposure to 1-2 mg/m3, far above that limit -- so post-construction dust removal needs damping down and H or M class vacuum extraction, not a dry brush. Where those controls cannot keep exposure down, HSE also sets out when RPE is needed.
What is the exposure limit for silica dust?
HSE's guidance on construction dust states: 'The Workplace Exposure Limit for silica is 0.1 mg/m3 when averaged over 8 hours.' Respirable crystalline silica (RCS) is present in common construction materials -- concrete, mortar, sandstone, granite -- and becomes airborne as fine dust when they are cut, drilled, ground, or disturbed during clearance and cleaning of construction debris.
Why is dry sweeping dangerous?
HSE's guidance warns that dry sweeping concrete dust and other building debris can produce high levels of dust, and that dry brushing in particular can quickly generate peak exposures of around 1-2 mg/m3 of silica -- ten to twenty times the 8-hour WEL. This is exactly the kind of activity a post-construction clean involves if the wrong method is used, which is why dry sweeping should be avoided wherever possible.
What controls should a cleaning contractor use instead?
HSE's practical guidance is to 'damp down and use a brush, shovel and bucket' for minor or small amounts of debris, and to use 'vacuum attachments fitted to an H or M class extraction unit' for finer material. A task-specific COSHH assessment should confirm which controls are needed before work starts, and a post-construction cleaning contractor should apply the same hierarchy as the trades that created the dust: suppress at source, then extract.
What if RPE is needed?
Where damping down and extraction cannot keep exposure below the limit, HSE's construction dust guidance identifies FFP3 as the most suitable respirator type for work that does or could involve silica dust. Anyone using a tight-fitting mask needs to be clean-shaven at the point of contact and face-fit tested -- either qualitatively or quantitatively -- to confirm it forms a proper seal.
Silica dust control hierarchy for post-construction cleaning
| Control | What it means | When to use it |
|---|---|---|
| Damp down | Water spray, then brush, shovel and bucket | Minor or small amounts of debris |
| H or M class vacuum extraction | Vacuum attachments fitted to a certified extraction unit | Finer dust and larger areas |
| RPE (e.g. FFP3) | Correctly fitted, clean-shaven contact, face-fit tested | Where damping down and extraction cannot keep exposure below the WEL |