Laboratory Study to Assess Causative Factors Affecting Temporal Changes in Filtering Facepiece Respirator Fit: Part I – Pilot Study

Abstract

The National Institute for Occupational Safety and Health is conducting a first-of-its-kind study that will assess respirator fit and facial dimension changes as a function of time and improve the scientific basis for decisions on the periodicity of fit testing. A representative sample of 220 subjects wearing filtering-facepiece respirators (FFR) will be evaluated to investigate factors that affect changes in respirator fit over time. The objective of this pilot study (n = 10) was to investigate the variation in fit test data collected in accordance with the study protocol. Inward leakage (IL) and filter penetration were measured for each donned respirator, permitting the calculation of face seal leakage (FSL) and fit factor (FF). The study included only subjects who (a) passed one of the first three fit tests (FF ≥ 100), and (b) demonstrated through a series of nine donnings that they achieved adequate fit (90th percentile FSL was ≤ 0.05). Following the respirator fit tests, 3-D scans of subjects were captured, and height, weight, and 13 traditional anthropometric facial dimensions were measured. The same data were collected 2 and 4 weeks after baseline. The mean change in FSL for the 10 subjects was 0.044% between Visits 1 and 2, and was 0.229% between Visits 1 and 3. Technicians achieved at least moderate reliability for all manual measurements except nose protrusion. Filter penetration was generally less than 0.03%. Geometric mean fit factors were not statistically different among the three visits. The large variability was observed with different respirator samples for the same model, between subjects (inter), and within each subject (intra). Although variability was observed, adequate fit was maintained for all 10 subjects. Pilot scans collected show subject faces remained the same over the 4 weeks. The consistent results during the pilot study indicate that the methods and procedures are appropriate for the 3-year main study. In addition, this baseline fit change data will be compared with future fit changes to determine if the changes are meaningful.

Temporal changes in filtering-facepiece respirator fit

“…Inward leakage (IL) consists of particle leakage through two pathways: respirator filter (filter penetration) and the interface between the respirator and a wearer’s face (faceseal leakage). A method for evaluating respirator fit by first determining IL by means of a test subject fit test was validated in a previous pilot study [7] and those methods were used for the current study. A PortaCount® Plus (Model: 8020A, TSI, Inc., Shoreview, MN) condensation particle counter (without the N95-Companion accessory) was used to measure IL of ambient particles ranging from 0.02 to > 1 μm.…”

“…[11] Based on results of a pilot study assessing changes in respirator fit over a four-week period, it was determined that this fit test method can adequately measure various variance components to allow accurate comparison of fit between visits. [7] …”

“…[5] A 2007 Institute of Medicine (IOM) study recommended that “NIOSH …perform research to determine which facial features have the greatest impact on respiratory protection of face masks in the workplace, using quantitative measures.” [6] In response to these recommendations, NIOSH first conducted a pilot study to verify consistent data collection methods and ensure that test results were reproducible. [7] This pilot study found that geometric mean fit factors for ten subjects were not statistically different among three visits which occurred over a four-week period. Large variability was observed with different respirator samples for the same model, between subjects (inter) and within each subject (intra).…”

Effect of Upper Strap Downward Displacement on N95 Filtering Facepiece Respirator Fit Factors: A Pilot Study

“…However, the modified procedure omits only two OSHA-measured parameters (i.e., talking, bending over) and modified fit-tests have been used in previous N95 FFR studies. (17–20) …”

Criteria for the Collection of Useful Respirator Performance Data in the Workplace

“…(34) Published data demonstrate they will not significantly increase penetration for current NIOSH-certified U.S. filters or their equivalents. (35,36) Nonetheless, if there is doubt or if significantly higher flow rates are considered, penetration measurements should be made using particle sizes representative of those found in the workplace. Potential for C i sample bias induced by the higher flow rate must also be investigated.…”