Quick answer: The dust you can see in a workshop settles. The dust that damages your lungs stays airborne for hours -- and you cannot see it. Fine respirable particles from grinding, cutting, sanding, routing, resin work and spray painting are measured in microns. At 10 microns and below they bypass the nose and throat entirely and reach the lung tissue. At PM2.5 and below they cross into the bloodstream. Silica dust, hardwood dust, metal fume and isocyanates from spray products are all classified as occupational carcinogens or respiratory sensitisers. A dust mask reduces some exposure. Correct extraction at source removes the hazard before it reaches the breathing zone. This series covers each workshop dust type in depth -- what it is, what it does, and what the right extraction looks like.
Watch any popular workshop YouTube channel and you will see it. The angle grinder kicking up a haze of metal dust. The router table throwing a cloud of fine wood particles across the workshop. The orbital sander leaving a visible film on every surface. The resin pour with fumes rising into the creator's face. The presenter working through it, sometimes in a dust mask, sometimes in nothing at all -- and the audience watching and absorbing the impression that this is just how workshop work looks.
It is. But what the camera does not show is what is happening in the air after the visible dust settles. The particles that cause silicosis, occupational asthma, hardwood dust adenocarcinoma and occupational COPD are not the ones you can see. They are the ones you cannot.
Why the invisible dust is the dangerous dust
Human airways are remarkably effective at filtering large particles. The nose, nasal passages and upper airways catch particles above approximately 10 microns in diameter -- they are trapped by mucus and expelled. This is why large visible dust makes you cough and sneeze. Your body is doing its job.
The particles below 10 microns -- PM10 and smaller -- are not caught by the upper airways. They reach the bronchi and bronchioles. Particles below 4 microns -- the respirable fraction -- reach the alveoli, the tiny air sacs where gas exchange happens. At this depth in the lung, the body has very limited ability to clear particles. They accumulate.
Particles below 2.5 microns -- PM2.5 -- can cross the alveolar membrane into the bloodstream. This is not a theoretical risk. It is the mechanism by which fine particulate causes cardiovascular disease, not just lung disease.
The particles generated by grinding metal, cutting concrete, sanding hardwood and routing MDF are overwhelmingly in the PM10 and PM2.5 range. The visible cloud you see in a workshop video is the large fraction -- already being caught by the upper airways. What you cannot see is the fine fraction that is not.
The specific hazards -- what each dust type does
Respirable crystalline silica (RCS)
Silica is present in concrete, brick, sandstone, engineered stone, some ceramics and some metals. Cutting, grinding and sanding these materials generates RCS -- particles small enough to reach the alveoli and cause silicosis. Silicosis is irreversible and progressive. Once established it continues to damage lung tissue even after exposure stops. It is also associated with increased lung cancer risk. The HSE Workplace Exposure Limit for RCS is 0.1 mg/m3 over an 8-hour shift. A brief burst of concrete grinding in an unventilated workshop can exceed this limit many times over. See: Concrete, stone and tile dust guide
Hardwood dust
Hardwood dust -- oak, beech, ash, walnut, mahogany -- is classified as a Group 1 carcinogen by the International Agency for Research on Cancer. It is specifically associated with adenocarcinoma of the nasal cavity and sinuses -- a rare cancer that is significantly more common in woodworkers than in the general population. The WEL for hardwood dust is 3 mg/m3 over 8 hours -- lower than for many other dusts because of the carcinogen classification. A router table or planer in an enclosed workshop can reach this level quickly without extraction. See: Woodworking and timber dust guide
Metal dust and welding fume
Fine metal dust from grinding, cutting and filing is a respiratory irritant and, in the case of some metals and alloys, a carcinogen. Welding fume was reclassified by the International Agency for Research on Cancer as a Group 1 human carcinogen in 2017 -- a reclassification that the HSE followed with updated enforcement guidance in 2019 requiring local exhaust ventilation for all welding operations. The YouTube workshop creator running a welder in a garage with no extraction and an open door is exposed to carcinogenic fume on every welding session. See: Metal grinding and welding fume guide
Resin, fibreglass and composite dust
Resin work generates hazards at two stages -- during the pour (styrene vapour from polyester resin, amine vapour from some epoxies) and during sanding and finishing of the cured material (fine resin particulate and fibreglass filaments). Some epoxy hardeners are respiratory sensitisers -- once sensitised, even tiny exposures trigger an asthmatic response that does not reverse. Fibreglass filaments are physically irritating to airway tissue. The resin art community on YouTube is particularly exposed because the combination of vapour during pour and dust during sanding is present in most projects, often in domestic spaces with no extraction. See: Resin, fibreglass and composite dust guide
Spray painting -- the one people notice, but often get wrong
Spray painting is the workshop activity where people most commonly wear respiratory protection -- but frequently the wrong type. A dust mask (FFP2 or FFP3) protects against particulate. It does not protect against chemical vapour. 2K automotive paint contains isocyanates -- the most common cause of occupational asthma in the UK. Isocyanates pass straight through a dust mask. The correct protection for 2K paint spraying is an air-fed hood or a full-face respirator with the correct combination filter for the specific product. A P3 filter alone is not sufficient for isocyanate-containing products. See: Spray painting and isocyanates guide
Dust masks -- what they do and what they do not do
A disposable dust mask -- FFP1, FFP2 or FFP3 -- filters particulate. FFP1 filters 80% of particles above 0.3 microns. FFP2 filters 94%. FFP3 filters 99%. These are the rated filtration efficiencies at the filter material. The actual protection factor depends on face fit -- a poorly fitting FFP3 mask provides no better protection than a well-fitting FFP2 because the leak is around the mask, not through the filter.
Dust masks do not protect against chemical vapours, gases or biological agents. They do not protect against welding fume unless specifically rated for metal fume (P3 class with appropriate filter combination). They are supplementary protection -- the last line of defence after engineering controls have reduced exposure as far as reasonably practicable.
Engineering control means extraction at source -- capturing the dust before it enters the air of the workshop. This is what M-Class and H-Class extraction equipment does. A dust mask on a face while fine RCS fills the workshop air is not adequate control. It is the approach of someone who does not know what is in the air.
What correct extraction looks like
On-tool extraction -- connecting an M-Class or H-Class dust extractor directly to the power tool generating the dust -- captures the dust at the point of generation before it enters the workshop air. This is the engineering control that the dust mask cannot replicate.
- M-Class extraction -- 99.9% filtration at 0.3 microns (H13 HEPA). The minimum standard for wood dust, concrete dust, general construction dust and most workshop applications. See: M-Class extraction hub
- H-Class extraction -- 99.995% filtration at 0.3 microns (H14 HEPA). Required for hardwood dust where carcinogen classification applies in a regulated workplace, for asbestos-containing materials, and for mould. The correct specification for the most hazardous workshop dusts. See: H-Class extraction hub
The full series
Metal grinding, fabrication and welding fume
Woodworking and timber dust
Resin, fibreglass and composite
Concrete, stone and tile -- respirable silica
Spray painting -- isocyanates and why a dust mask is not enough
Related pages
M-Class extraction | H-Class extraction | COSHH Regulations 2002 | HSE EH40 Workplace Exposure Limits | Construction hub
