Variability in respiratory protection and the assigned protection factor

Area of Science:

• Occupational health and safety
• Industrial hygiene
• Biostatistics

Background:

• Workplace protection factor (WPF) variability is crucial for respirator effectiveness.
• Existing analyses often assume lognormal distributions but don't separate within- and between-wearer variability.
• Accurate assessment of respirator performance requires accounting for individual wearer differences.

Purpose of the Study:

• To develop an analytical framework for respirator WPF data using a normal random effects model.
• To propose a method for establishing an assigned protection factor (APF) that incorporates variance components.
• To re-evaluate the APF for half-mask respirators based on empirical data.

Main Methods:

• Analysis of log-transformed and logit-transformed penetration (P) values from seven studies of half-mask and two studies of powered air-purifying respirators.
• Application of maximum likelihood estimation to a normal random effects model.
• Development of an APF method ensuring <5% of WPFs are below APF for individuals and populations.

Main Results:

• The within-wearer variance component generally dominated the between-wearer component.
• APF calculations using log-transformed and logit-transformed P values showed good agreement.
• For half-mask respirators, estimated APFs ranged from 1.4 to 250, with most studies yielding an APF ≤ 5.3.

Conclusions:

• The proposed random effects model effectively partitions WPF variability.
• The new APF method provides a statistically sound approach to respirator selection.
• A reduction of the assigned protection factor for half-mask respirators from 10 to 5 is recommended.