Household Dirt

THE PROBLEM:

A major household products company faced a challenge from a rival company, claiming that its product was better at cleaning household dirt. Contesting this claim on the grounds that the dirt the rival company used was not representative of real household dirt, the company called MVA Scientific Consultants.

Analysis of household dust by light microscopyCharacterization of dust by light microscopy

THE ANALYSES:

Analyses were performed on vacuum samples collected from homes in 7 geographically diverse metropolitan areas of the United States to gain information about the major components of household dirt. The household dirt samples were characterized by both gravimetric measurement of sieved size fractions and by polarized light microscopy (PLM) analyses.

THE OUTCOME:

The results showed that skin cells, soil minerals, plant fragments, hair, cotton fibers, and starch granules made up over 90% of household dirt.

The fiber fraction of the dirts ranged from 9% to 89% with a mean of 46%. The ratio of hair to natural and man made fibers (lint) in the fiber fraction was extremely variable, from 0.05 to 0.95, with a mean of 0.41.

On average, about 40% of the mass of the particulate (non-fibrous) portion was greater than 300 um, about 10% was between 75 to 300 um, and about 3% was below 75 um.

In addition to a written report, MVA scientists were available to testify as expert witnesses that the “dirt” used by the rival household products company was unlike any actual household dirt. The rival company was forced to change their marketing claims.