Abstract

Certain respiratory protective equipment (RPE) must fit tightly to the face of the wearer to provide effective protection, yet it is still unclear to what extent facial features affect mask performance. This study aimed to assess how facial dimensions affect the efficacy of a given RPE.

We tested a single RPE (3M 8835+) on participants (n=262) who consistently wear RPE at work. Three facial dimensions were measured to limit the demands placed on test participants: face length, face width, and jaw width. Mask test and facial measurements were conducted by the same researcher using the HSE standardised face fit testing protocol. The participants represented 22 different industries, the majority (90%) of whom were male. Fit factor (FF), representing the ratio of the exposure concentration outside to inside a mask, used to assess mask fit, with FF >100 constituting a successful fit.

Although 94.7% (n=248) of the study population achieved a successful fit, there was considerable variation among test results: FF median=415; Interquartile Range (IQR)=294–604. FF was log-transformed for regression analyses, which identified FF increases of 11.9% (p<0.05) and 18.3% (p<0.005) per 10% increase in the ratio of face length to jaw width and face width to jaw width, respectively.

These results help understand the impact face shape can have on the effective seal achieved by RPE and could help inform mask design to maximise impacts for respiratory health. Further analysis of the data may expand on the impact of face shape on RPE seal during the specific face fit test exercises.