Relationship of Protective Mask Seal Pressure to Fit Factor and Head Harness Strap Stretch

Abstract : Currently, protective mask seals are evaluated indirectly by measuring fit factor (FF), a ratio of the concentration of particles outside versus the concentration of particles inside the mask. This report describes an alternate process for evaluating mask seals by measuring seal pressure distribution. The goal was to develop a relationship between FF and seal pressure for evaluating seal performance, and relationships between FF and strap stretch and between seal pressure and strap stretch for determining proper strap adjustment. Pressure was measured using a thin film flexible sensor placed at 11 locations around the seal of an M40 mask on a headform. Corresponding FF was measured using a protective mask fit tester. Stretch in each of the six head harness straps was measured manually using a caliper and gauge length markers on the strap. Measurements were made for three degrees of strap tightness over a total of 22 trials.

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