Development of an advanced respirator fit-test headform

Abstract

Improved respirator test headforms are needed to measure the fit of N95 filtering facepiece respirators (FFRs) for protection studies against viable airborne particles. A Static (i.e., non-moving, non-speaking) Advanced Headform (StAH) was developed for evaluating the fit of N95 FFRs. The StAH was developed based on the anthropometric dimensions of a digital headform reported by the National Institute for Occupational Safety and Health (NIOSH) and has a silicone polymer skin with defined local tissue thicknesses. Quantitative fit factor evaluations were performed on seven N95 FFR models of various sizes and designs. Donnings were performed with and without a pre-test leak checking method. For each method, four replicate FFR samples of each of the seven models were tested with two donnings per replicate, resulting in a total of 56 tests per donning method. Each fit factor evaluation was comprised of three 86-sec exercises: "Normal Breathing" (NB, 11.2 liters per min (lpm)), "Deep Breathing" (DB, 20.4 lpm), then NB again. A fit factor for each exercise and an overall test fit factor were obtained. Analysis of variance methods were used to identify statistical differences among fit factors (analyzed as logarithms) for different FFR models, exercises, and testing methods. For each FFR model and for each testing method, the NB and DB fit factor data were not significantly different (P > 0.05). Significant differences were seen in the overall exercise fit factor data for the two donning methods among all FFR models (pooled data) and in the overall exercise fit factor data for the two testing methods within certain models. Utilization of the leak checking method improved the rate of obtaining overall exercise fit factors ≥100. The FFR models, which are expected to achieve overall fit factors ≥ 100 on human subjects, achieved overall exercise fit factors ≥ 100 on the StAH. Further research is needed to evaluate the correlation of FFRs fitted on the StAH to FFRs fitted on people. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a file providing detailed information on the advanced head form design and fabrication process.].

Figure 1

Static Advanced Headform Test Setup (color figure available online).

Figure 2

Digital comparison of dimensions of NIOSH Medium digital headform (d-HF) file and Static Advanced Headform (StAH) in a) front, b) left side, c) right side, and d) rear views. The vertical scale to the right of each figure ranges from +5 mm (red) to -5 mm (violet); the colors on the headform show the corresponding registration differences. The d-HF file is the reference for each registration (color figure available online).

Figure 3

Overall Exercise Fit Factors by FFR Model and Testing Method. *Notations following FFR Model name: “+S” = Screening method used.“ −S” = Screening method not used. Notes: 1) n = 8 for each FFR model / test method combination (i.e., 8 data points make up each box plot). 2) Vertical lines on the boxplots show (from left to right) lowest value, 25th %ile, 50th %ile, 75th %ile, and highest value. 3) The dashed blue line at 200 indicates the demarcation of overall exercise fit factor (FF_O) above and below 200. Results > 200 are shown in the shaded orange area of the graph. Our study utilized a non-commerical version of the FitPlus software to record FF_O > 200. The commercial version of the software limits the FF_O output to a maximum of 200 (color figure available online).