Work of Breathing for Respiratory Protective Devices: Method Implementation, Intra-, Inter-Laboratory Variability and...

Area of Science:

• Occupational Health and Safety
• Biomedical Engineering
• Industrial Hygiene

Background:

• The International Organization for Standardization (ISO) Technical Committee 94/Subcommittee 15 (TC 94/SC 15) adopted Work of Breathing (WOB) for respiratory protective device (RPD) performance standards.
• The National Institute for Occupational Safety and Health's (NIOSH) National Personal Protective Technology Laboratory (NPPTL) aimed to compare this proposed WOB method with existing resistance measurement techniques for RPDs.

Purpose of the Study:

• To establish a method for measuring RPD airflow resistance that conforms to ISO SC15 standards.
• To validate the operational performance and conformance of the WOB measurement method.
• To assess the repeatability and reproducibility of WOB measurements for various RPD designs.

Main Methods:

• Implemented WOB measurement procedures following ISO 16900-5:2016 and ISO 16900-12:2016 standards.
• Utilized volume-averaged total work of breathing (WOB_T/V_T) for evaluating airflow resistance, analyzing variation and bias using standard orifices.
• Tested both standard orifices and actual RPDs (air-purifying and supplied-air) to verify method accuracy and repeatability.

Main Results:

• Preliminary verification using standard orifices confirmed the method met ISO requirements and showed equivalence with other laboratories.
• RPD testing demonstrated compliance based on tidal volume and frequency, with appropriate adjustments reducing average absolute bias to 1.7%.
• The average coefficient of variation for WOB_T/V_T was 2.3%, with over 97% of results meeting specifications during extended use; WOB_T/V_T measurements were repeatable (p<0.05) for various RPD types.

Conclusions:

• The NIOSH NPPTL successfully implemented and validated the ISO WOB method for RPDs, consistently providing ISO-compliant verification.
• The method demonstrated high repeatability and reproducibility for appropriately sealed RPDs, with an average bias of 1.7%.
• WOB_T/V_T measurements for unsealed half-mask RPDs were 31% lower than for sealed ones, highlighting the importance of proper sealing in performance testing.