Evidence grade: A2 — Institutional literature / B1 — Industry practice Effort: N/A — reference, no procedure
Not microplastics, exactly — "micro-fiberglass" or composite dust is the accurate term. Sanding fiberglass-reinforced plastic (FRP) releases a mix of tiny glass fibers and particles of the cured resin they're embedded in. Calling it microplastics is imprecise, but the underlying worry is legitimate: the dust is a real inhalation hazard, and researchers have traced sanding and cutting debris from marinas and boat yards into surrounding waters.
What the dust actually is
FRP is glass fibers locked in a cured thermoset resin — usually polyester or epoxy. Sanding it breaks both apart, so the dust is a composite: silica-based glass fibers plus fragments of cured resin. As marine eco-toxicologist Juan José Alava puts it, fiberglass particles are "silica‑based glass fibres, often reinforced with plastic" [2]. Whether a given particle counts as "microplastic" depends on its composition — a pure glass fiber isn't plastic; a resin fragment largely is. "Micro-fiberglass" sidesteps the definitional fight and is the term the researchers use.
The health side: treat it as hazardous dust
Fiberglass product safety sheets list OSHA nuisance-dust limits of 5 mg/m³ (respirable) and 15 mg/m³ (total), and instruct users to avoid breathing the dust and to clean up with a wet mop or vacuum rather than dry sweeping [1]. Standard workshop practice follows from that: a P2/N95-class respirator at minimum, sealed eye protection, gloves and long sleeves (the fibers itch for a reason), and wet sanding or dust extraction wherever possible. Stop rule: dry sanding or grinding FRP with no respiratory protection and no dust control — stop and set up controls first.
The environment side: it doesn't stay in your yard
A 2026 Simon Fraser University study of the Cowichan Estuary found fiberglass particles at 96% of sediment testing stations, with concentrations highest near industrial activity — and at marinas, slipways, and boat-maintenance areas "where sanding, repairs and hull cleaning are common" [2]. The study's recommendations include tighter controls on slipways and boat yards specifically to reduce sanding and cutting debris entering surrounding waters. Fiberglass is denser than seawater, so it settles and accumulates in sediment rather than washing away [2]. Whatever your local setting, don't wash sanding dust into storm drains or onto bare soil: collect it, bag it, bin it.
Honest limits
- The long-term toxicity of environmental fiberglass particles is not established — "we don't yet know what levels of fiberglass exposure cause harm," the study's lead author says [2]. Treat this as precautionary, not proven.
- OSHA's limits above are generic nuisance-dust limits, not fiberglass-specific exposure standards.
- "Micro-fiberglass" is the researchers' term; regulators and product sheets may use "fiberglass dust" or "composite dust." The classification of individual particles (glass vs. resin) depends on composition — unverified for any specific dust sample without lab analysis.
Sources
- Fiberglass product safety data sheet — OSHA nuisance-dust limits (5 mg/m³ respirable / 15 mg/m³ total); "avoid breathing dust"; clean with wet mop or vacuum — https://images.thdstatic.com/catalog/pdfImages/a5/a545831f-2bac-4acb-8f8b-6bcd53f0f11f.pdf
- Technology Networks (reporting SFU research) — "Fiberglass Buildup in Estuary Sparks Safety Concerns"; Alava JJ et al., Marine Pollution Bulletin 2026;224:119187 — fiberglass particles at 96% of sediment stations; higher at marinas/slipways/boat-maintenance areas; recommendation for tighter controls on sanding and cutting debris — https://www.technologynetworks.com/tn/news/marine-fiberglass-pollution-found-in-key-vancouver-island-estuary-410039
Repair Lab · Release 1 · Evidence last checked September 30, 2026 · A project of AOJEL