Microvacuum Sampling

Microvacuum sampling is a way of collecting settled dust from a measured area of a surface by drawing it through a small nozzle into a filter cassette with a low-flow air pump. The filter is then analyzed by electron microscope, and the result is reported as asbestos structures per square centimeter of surface.

Origin

The method grew out of building and abatement work in the 1980s and 1990s, when investigators needed a repeatable way to measure asbestos on surfaces. ASTM standardized it as ASTM D5755, first issued in the 1990s, with a later companion method for reporting results by mass.

Significance in Asbestos Context

Microvacuum results can show that a room, ship compartment, vehicle or home was contaminated with asbestos and that fibers had spread beyond the place they were released. In litigation they are used to support take-home, bystander and building claims, and to show that a product shed fibers when it was handled or aged. Defendants often challenge them: the method counts small structures that may not be the size measured in air sampling, results vary with the surface and the technique, and there is no regulatory limit to compare them with. Plaintiffs' experts usually compare results with background levels from ordinary buildings and treat them as proof of contamination and of a route of exposure, not as a measure of how much a person inhaled. How a court treats these results can vary by jurisdiction and by expert.

Example Sentence

The industrial hygienist took microvacuum samples from the top of the garage cabinets where the brake parts had been stored and found chrysotile in every sample.

Related Terms

Settled Dust, ASTM D5755, Wipe Sampling, ASTM D6480, Transmission Electron Microscopy (TEM), Take-home Exposure, Industrial Hygiene Sampling

Notes

• Ask whether samples were taken by an accredited inspector and analyzed by an accredited laboratory, with chain-of-custody records.
• Results are reported per square centimeter of surface, not per cubic centimeter of air; they are not directly comparable to OSHA air limits.
• Photographs of where each sample was taken make the results much more useful later.