Settled Dust

Settled dust is dust that has fallen out of the air and collected on floors, ledges, furniture, clothing or equipment. When asbestos fibers are released, many end up in this dust, so testing it can show that a building, vehicle or home was contaminated, even years after the work that released the fibers.

Origin

Industrial hygienists have long noted dust deposits as a sign of poor dust control, but systematic testing of settled dust for asbestos developed in the 1980s and 1990s, when building surveys and litigation called for ways to measure contamination on surfaces. ASTM later published standard methods for collecting it by microvacuum and by wipe.

Significance in Asbestos Context

Air samples show what was in the air for a few hours; settled dust shows what built up over time. That makes it useful evidence in take-home exposure cases (dust on work clothes, in cars, in laundry areas), in building and school cases, and in product cases where a material shed fibers onto surrounding surfaces. Dust that is disturbed by sweeping, shaking out clothes or blowing with compressed air can put fibers back into the air, which is how family members and bystanders were often exposed. There is no federal limit for asbestos in settled dust, so results are usually compared with background levels found in ordinary buildings, and experts disagree about how surface counts relate to what a person actually breathed. Courts and juries generally treat settled-dust results as evidence of contamination and of a pathway for exposure, rather than as a direct measure of dose.

Example Sentence

Microvacuum samples of the settled dust on the boiler room ledges showed chrysotile at many times the levels found in the office wing of the same building.

Related Terms

Microvacuum Sampling, Wipe Sampling, ASTM D5755, Take-home Exposure, Bystander Exposure, Fiber Release, Exposure Reconstruction, Transmission Electron Microscopy (TEM)

Notes

• Do not sweep, vacuum with an ordinary vacuum, or shake out dust you think may contain asbestos; leave testing to a licensed inspector.
• If a home, garage or workplace may still hold old dust, tell your lawyer before it is cleaned or renovated; it may be evidence.
• Keep any old work clothes, bags or tools that were never washed, sealed in a plastic bag.