Effects of Environmental and Carpet Variables on Vacuum Sampler Collection Efficiency

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Abstract
Vacuum sampling has been widely employed to investigate lead exposure in children and establish correlations between children's blood lead levels and dust lead loading on contact surfaces. The lack of information about the collection efficiency of the sampling devices used in many studies, however, limits the reliability of reported results. As part of the Childhood Lead Exposure Assessment and Reduction Study, an extensive investigation was completed to define the relationship between the collection efficiency of a vacuum sampler and four specific factors: carpet type, relative humidity, vacuum capture velocity, and dust loading. Test dust from residences with lead paint hazards was sieved to remove particles larger than 500 μm in diameter and was embedded in carpets using the American Society for Testing Materials standard method (F 608–89) for spreading dust. The results from the efficiency studies showed that each factor, both individually and jointly, affected the vacuum sampler collection efficiency. The measured particle collection efficiency varied from 60 to 89 percent in the level loop carpets, with the best efficiencies at summertime humidity levels (60 to 85%). For shag carpet, collection efficiency varied from 39 to 85 percent, with efficiencies below 50 percent occurring mainly at low relative humidity and with low or medium vacuum velocities (10.5 and 13.5 m/s). The relative humidity has an important effect on the vacuum sampling efficiency of shag rugs. The intensity of electrostatic charges on the carpet surface are different for different relative humidities in the environment. An empirical equation to estimate carpet dust loading from vacuumed dust mass and relative humidity is presented.