Generation of respirable glass fiber aerosols using a fluidized bed aerosol generator

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Abstract
A fluidized bed aerosol generator was used to produce respirable aerosols containing predominately single glass fibers. Two fiber types were aerosolized, a large diameter commercial insulation fiber and a smaller diameter experimental glass fiber. Aerosols produced by the fluidized bed generator were characterized as to concentration, fiber length and fiber diameter using scanning electron microscopy. A point-to-plane electrostatic precipitator used to collect fibers was found to preferentially deposit fibers>0.1 micrometer in diameter at an angle to the collection surface. A method to eliminate this sampling artifact is described. Generator operating parameters were found to influence the characteristics of the aerosol produced. For the smaller fibers, increasing the air flow through the generator from 25 to 45 liters/minute decreased the median aerosolized fiber length from 7.2 to 5.9 micrometers but did not alter fiber diameter (0.2 micrometers). Aerosol output from the generator varied from 2.1 to 4.0 mg/min as the generator flow rate varied from 25 to 38 liters/minute. Increasing the bed volume from 100 to 200 milliliters increased the aerosol output from 1.4 to 4.2 mg/min under constant air flow conditions. The aerosol produced changed slowly with time. The median length decreased from 6.9 to 4.7 micrometers in 28 minutes and the aerosol output dropped to a plateau of 10% of its initial value after 15 minutes of operation. This output level persisted for at least 100 minutes.