Million Particles per Cubic Foot (mppcf)

Million particles per cubic foot (mppcf) is the unit used to report dust levels before fiber counting replaced it. It counts all visible dust particles in a cubic foot of air, whether or not they are asbestos fibers.

Origin

The unit came from counting impinger samples under the light microscope. In 1938 the U.S. Public Health Service proposed 5 mppcf as a tentative limit for asbestos dust, and the American Conference of Governmental Industrial Hygienists adopted 5 mppcf as its threshold limit value in 1946. It remained the reference figure until fiber-based limits were adopted around 1970.

Significance in Asbestos Context

Exposure reconstructions for work before about 1970 often have to convert mppcf into fibers per cubic centimeter (f/cc) to estimate cumulative dose. There is no single conversion factor: the ratio varied by industry, by process and by the sampling and counting method, and published factors differ widely. A dose estimate that depends on one factor should say which it used and why. Historically, the 5 mppcf guideline is also evidence of what industry and government considered acceptable at the time, which bears on state-of-the-art arguments.

Example Sentence

The industrial hygienist converted the 1960s readings of 8 to 15 mppcf into fiber counts using a range of published factors, rather than a single figure.

Related Terms

Midget Impinger, Threshold Limit Value (TLV), Fibers per Cubic Centimeter (f/cc), Cumulative Exposure, Fiber Year, State-of-the-Art Defense

Notes

• Ask any expert who converts mppcf to f/cc to show the factors used and how sensitive the result is to them.