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AbstractA limited number of published studies have evaluated concentrations of airborne fibers in outdoor air, with even fewer assessing typical air concentrations in the ambient air near fiberglass wool manufacturing facilities. Building upon the assessment by Switala et al. (1994), area samples for airborne fiber concentrations (diameters of less than 3 µm, lengths greater than 5 µm, and aspect ratios equal to or greater than 5 to 1) were collected at fixed locations along the fence lines of three fiberglass wool manufacturing facilities in the United States. Samples were analyzed by the National Institute for Occupational Safety and Health (NIOSH) Method 7400, via phase contrast microscopy (PCM) using “B” counting rules. A total of 134 samples were collected across the three plants. Overall, 73% of the samples collected were below the limit of quantification (LOQ). Using the Kaplan–Meier (KM) method for estimation of values below the LOQ, the geometric mean fiber concentration for all plants combined was 0.0028 fibers per cubic centimeter (f/cc), with the 95th percentile upper confidence level at 0.0049 f/cc. Of those samples with detectable concentrations of airborne fibers (n = 36), when further analyzed using energy dispersive X-ray (EDX) analysis, only one sample had a detectable glass fiber concentration at 0.0045 f/cc, which was noted as the detection limit for the method. This glass fiber concentration is within the range anticipated for ambient fibrous glass near production facilities, suggesting consistency with measurements made by Switala et al. (1994), despite changes in production methods (i.e., use of different binders) since 1994 and the use of updated methods for treatment of values below the LOQ in the current assessment. [ABSTRACT FROM AUTHOR]