Fit test for filtering facepieces: search for a low-cost, quantitative method

Area of Science:

• Occupational Health and Safety
• Respiratory Protection
• Aerosol Science

Background:

• Conventional respirator fit-testing methods are unsuitable for low-efficiency filtering facepieces.
• These masks rely on both filter material and face seal for protection.
• Accurate assessment of face-seal integrity is crucial for optimizing respirator design and user application.

Purpose of the Study:

• To develop a novel method for assessing the face-seal effectiveness of filtering facepiece respirators.
• To differentiate between face-seal leakage and filter penetration in respirator performance.
• To introduce a sensitive indicator of respirator fit applicable to various filter materials.

Main Methods:

• A unique difference in aerosol penetration at low versus high flow rates was identified.
• This difference was utilized to distinguish face-seal leakage from filter penetration.
• A 'fit index' was calculated by comparing aerosol concentrations at different flow rates.

Main Results:

• A novel 'fit index' was introduced as a sensitive indicator of respirator fit.
• The fit index demonstrated unified behavior across different filter materials when normalized.
• Tests on human subjects during normal breathing correlated well with breath-holding experiments.

Conclusions:

• The developed fit index provides a reliable method for evaluating respirator face-seal performance, especially for low-efficiency filters.
• This approach allows for the differentiation of leakage and filter penetration, crucial for respirator development and selection.
• Further modifications to existing instruments are needed for human testing applications.