End user exposures to man-made vitreous fibers: I. installation of residential insulation products

An investigation was undertaken to develop a comprehensive characterization of end user exposures to residential man-made vitreous fiber insulation products in terms useful for future study of potential health outcomes. Nearly 1200 air samples were collected and analyzed gravimetrically or by phase contrast microscopy or scanning electron microscopy to describe worker exposure in eight homogeneous exposure groups defined by man-made vitreous fiber product and occupation. These samples represent the exposure of 99 different workers insulating 107 different houses in 11 states in the eastern and central United States. Gravimetric and fiber count exposure concentrations are reported in terms of task length and full shift time-weighted averages (TWAs). Results of this study indicate mean task length airborne fiber concentrations determined by phase contrast microscopy (PCM) using the National Institute for Occupational Safety and Health (NIOSH) Method 7400 “B” rules to be less than 1.0 fibers/cm³ for all homogeneous exposure groups except installers and feeders of loose fiberglass without binder (7.67 and 1.74 f/cm³, respectively) and installers of loose mineral wool (1.94 f/cm³). PCM fiber exposure estimates using “A” counting rules, although slightly higher, provided generally similar results. Because residential Insulators actively install insulation for only 1 to 4 hours on a typical day, comparable mean 8-hour TWA airborne fiber concentrations determined by PCM using NIOSH Method 7400 “B” rules were less than 0.3 f/cm³ for all homogeneous exposure groups except installers and feeders of loose fiberglass without binder (1.96 and 0.85 f/cm3, respectively) and installers of loose mineral wool (0.97 f/cm3). Because of the presence of other fibers, manmade vitreous fiber exposure estimates resulting from scanning electron microscopic analysis of samples using NIOSH counting rules were slightly less than corresponding PCM estimates for every homogeneous exposure group except installers and feeders of loose fiberglass without binder. The higher exposure estimates for these homogeneous exposure groups resulted from the presence of a significant number of thin fibers that were below the limit of resolution of PCM. Fiber size distributions determined by scanning electron microscopy showed geometric mean fiber diameters to range from approximately 1 to 2 fim for all homogeneous exposure groups except installers and feeders of loose fiberglass without binder that both had geometric mean fiber diameters of 0.6 nm.