A Pilot Study of the Measurement and Control of Deep Dust, Surface Dust, and Lead in 10 Old Carpets Using the 3-Spot Test While Vacuuming

This pilot study measured and examined the relationship between surface dust, deep dust, lead (Pb), and the 3-spot test during vacuuming of carpets. The 3-spot test measures the total time in seconds for the indicator light on a Hoover vacuum with dirt detector (HVDD) to turn from red to green on three spots 3 feet apart at least 4 feet from an entrance door. Ten older carpets were sampled in the Seattle area by using the following: (1) a 3-spot test to estimate the deep dust; (2) measuring the surface dust in g/m² with the High-Volume Small Simplified Surface Sampler; (3) vacuuming with an HVDD to extract a portion of the deep dust in g/m²; and (4) repeating this cycle of a 3-spot test, surface dust sample, and deep dust sample until the clean-carpet criteria was reached. Dust particles <150 μm were analyzed for Pb. The surface dust, deep dust, and dust collection rate (g/min) decreased rapidly at first and then much more slowly as vacuuming continued. The initial 3-spot test ranged from 12 to 110 seconds (median 40). The starting surface dust loading was 0.7 to 21.1 g/m² (median 2.9 g/m²), and it decreased by 84% to 99% when the deep dust was removed. Total dust—the sum of the surface dust and deep dust—ranged from 8.3 to 465 g/m² (median 63.2 g/m²). It took from 2.3 to 92 min/m² (median of 7.5 min/m²) to remove the total dust. The starting dust collection rate of 3.8 to 37 g/min decreased to final rates of 0.5 to 4.3 g/min. The 3-spot test (seconds) correlated with total dust (g/m²) (r = 0.63, p = 0.037) and cleaning time (min/m²) (r = 0.50, p = 0.12) when the data were log transformed. This study supports the utility of the 3-spot test. It tends to provide families and professional carpet cleaners with a quick and low-cost estimate of the deep dust present and the time required to clean carpets as well as indicating when the carpet is clean. Deep dust tends to accumulate in older carpets and becomes surface and airborne dust after activity on a carpet. Monitoring and removing the deep dust in old carpets may decrease the exposure of infants and sensitive adults to Pb, allergen, and other pollutants in house dust.