Comparison of NIOSH Method 7400 A and B Counting Rules for Assessing Synthetic Vitreous Fiber Exposures

Abstract

A number of counting rules are available to quantify airborne concentrations of synthetic vitreous fibers (SVFs), including the National Institute for Occupational Safety and Health (NIOSH) Method 7400 A and B rules and the World Health Organization European Reference Method for Man-Made Mineral Fibers. Differences in counting rules have led to a lack of comparability of sampling results across studies. The purpose of this article is to compare NIOSH Method 7400 A and B fiber counts using samples collected as a part of a large assessment of end-user exposures to SVFs. This comparison provides a link between previous investigations that utilized A rules and more recent investigations that used B rules. A total of 792 airborne fiber samples were collected according to NIOSH Method 7400 and separately evaluated using both NIOSH A and B counting rules. The results of this investigation indicate that A-rule fiber counts give statistically higher fiber density estimates than corresponding B-rule fiber counts, w...