This paper describes the theoretical basis upon which a test system has been set up to evaluate the sampling error associated with in-facepiece sampling on half-mask respirators. The in-facepiece sampling technique evaluated in this study is the one currently used in the U.S. to conduct quantitative facepiece fit testing. An experimental design was developed to study the sampling bias associated with in-facepiece sampling when selected parameters of the man/respirator system were varied. The results indicated that significant errors can be made in estimating concentration within a respirator when the current in-facepiece sampling technique is employed. Sampling bias was determined when in-facepiece samples were collected only during the inhalation phase of the respiratory cycles. They were found to range from greater than -99% to greater than +98%. The mean sampling bias was -17 +/- 38%. When measured in-facepiece concentrations were used to calculate a fit factor the resulting range was 44 to 4728 even though the actual fit factor was only 87. Based upon the data presented, it was hypothesized that faceseal leakage was streamlining within the respirator cavity. As a result, quantitative facepiece fit data on half-mask respirators may be biased by the large measurement error.
A study was conducted at a secondary smelter to evaluate the workplace performance of the 3M Model W-344 and Racal Model AH3 powered air-purifying respirators ( PAPR ) equipped with helmets and high efficiency filters. The research protocol developed for obtaining leakage measurements in the field provides for proper respirator fitting, use, wear, maintenance and worker supervision, all of which are problems commonly associated with data acquisition when field testing respirators. The protocol proved to be very workable, even though it required extensive worker and equipment monitoring. Based upon the successful implementation of this protocol, the performance of these PAPRs should be indicative of their best performance under the workplace conditions experienced in this study. This research protocol is proposed as a model for conducting field studies on other types of respirators as well as the basis on which to develop new and improved field test procedures. The results of one such study are presented in a comparison paper.
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