CAUSES OF IN-FACEPIECE SAMPLING BIAS—I. HALF-FACEPIECE RESPIRATORS <xref ref-type="fn" rid="fn1"><sup>*</sup></xref>

Abstract

A widely used technique of in-facepiece sampling has been shown to provide unrepresentative sampling in half-facepiece respirators. These experiments were conducted on a manikin test system using acetone vapour as a test agent. The magnitude of the sampling bias was non-uniform and appears to be a function of several sampling, facepiece and human parameters. These include the location and depth of the sampling probe, the position of the face-seal leak (nose vs chin, etc.), an interaction of breathing pattern (nose vs mouth) with the position of the face-seal leak, and the particular design of half-facepiece. These results clearly demonstrate that during inhalation inboard face-seal leakage does not mix uniformly within the cavity of a half-facepiece respirator. This leads to the collection of unrepresentative samples. The uses and interpretations of in-facepiece sampling data are discussed with regard to the effect of these large, non-uniform sampling biases. Within the constraints and design of the experiments, leak geometry, multiple leaks and volumetrically different leak rates were not found to be significant problems when conducting in-facepiece sampling on half-facepieces.