Assessment of Fiber Deposition on the Conductive Sampling Cowl in the Refractory Ceramic Fiber Industry

Abstract

The National Institute for Occupational Safety and Health (NIOSH) analytical method 7400 for fiber analysis recently has been challenged regarding the source of error that may be introduced when airborne fibers adhere to the inner surface of the conductive sampling cowl. In this study, the problem of fiber loss to the cowl is examined specifically as a part of the environmental monitoring quality assurance program of a major Refractory Ceramic Fiber (RCF) project.

The experimental procedure involved using NIOSH method 7400 for the analysis of 113 25-mm mixed cellulose ester (MCE) filters from sampling airborne RCF in the work environment. The extension cowls from these samples were washed, the particulate redeposited on 25-mm MCE filters, and analyzed in the same manner as the original sampling filters. There was an overall fiber deposition to the cowl of 16.5 percent. In 88 percent of the cowls, fibers on the cowl were visible to the eye; where no fibers were visible, the deposition on the extension cowl was negligible. There was no overall significant correlation between fiber deposition on the cowl and airborne fiber concentration. The type of work activity being performed did have a significant effect on the fiber deposition. It is concluded that fiber deposition is difficult to predict in this group of samples, and accurate determinations of airborne fiber concentration must include a cowl washing procedure.

The manner of sample handling during shipment was also investigated and found to have no statistically significant effect on fiber loss to the cowl; however, the small number of samples may have prevented the detection of any true differences.