Evaluation of exhalation resistance and inspired carbon dioxide concentration in elastomeric half-mask respirators with modified or covered exhalation valves

Details

• Corporate Authors:
  National Institute for Occupational Safety and Health
• Description:
  "This study explores the impact of modifying or covering the exhalation valves of an EHMR on exhaled breathing resistance and inspired CO2. Two approaches were considered: (1) modifying EHMRs to filter the exhaled breath through the inhalation filters
  
  (2) covering EHMR exhalation valves with surgical masks. Nine EHMR configurations approved by NIOSH were included in this study, where the "configurations" were the combination of a facepiece, filter, and other required components. These nine EHMR configurations were selected from three different respirator manufacturers and five different facepiece models. Four of the five facepiece models were assessed in both N95 and P100 filter configurations, and one facepiece model was assessed in a P100 filter configuration only. Exhalation resistance and inspired CO2 level were measured in each of the nine EHMR configurations under four study conditions, for a total of 72 measurements: (1) No EHMR modifications or coverings - experimental control
  
  (2) EHMR modified to filter exhaled breath through inhalation filters
  
  (3) EHMR exhalation valves covered with Level 1 surgical mask (per ASTM F2100)
  
  and (4) EHMR exhalation valves covered with Level 3 surgical mask (per ASTM F2100). Both exhalation resistance and inspired CO2 level were measured in accordance with NIOSH Standard Testing Procedures. For the exhalation resistance measurement, three samples were each donned one time (n=3) on a manikin, which was made to simulate exhalation at a constant airflow rate of 85 L/min. The initial resistance was then measured. For the inspired CO2 level measurement, one sample was donned three times each (n=3) on a manikin, which was made to simulate breathing at a rate of 14.5 breaths/min and a tidal volume of 0.724 L. The simulated exhaled breath consisted of 5% CO2, and the inspired CO2 concentration was measured at 40 Hz and averaged over three respiratory cycles. Test results showed that all EHMR configurations under all test conditions met the NIOSH exhalation resistance performance requirement of not exceeding 25 mmH2O. Eight of nine configurations modified to filter the exhaled breath showed measurable increases in mean exhalation resistance compared to their respective controls, increasing from between 4.40 and 9.48 mmH2O in the controls to between 8.21 and 18.5 mmH2O in the modified configurations. All configurations covered with Level 1 or Level 3 surgical masks also showed measurable increases in mean exhalation resistance compared to their respective controls, increasing from between 4.40 and 9.48 mmH2O in the controls to between 7.11 and 17.6 mmH2O in the covered configurations. The lowest of the three inspired CO2 level measurements for all EHMR configurations under all test conditions was less than 2%, with one observation of one configuration modified to filter the exhaled breath exceeding 2%. All nine EHMR configurations modified to filter the exhaled breath showed measurable increases in mean inspired CO2 levels compared to their respective controls, increasing from between 0.47% and 1.03% in the controls to between 1.25% and 1.94% in the modified configurations, while the inspired CO2 levels of EHMRs covered with Level 1 or Level 3 surgical masks did not consistently increase across all configurations, changing from between 0.47% and 1.03% in the controls to 0.80% and 1.26% in the covered configurations. Findings indicate that EHMRs can meet the NIOSH exhalation resistance performance requirement after being (1) modified to filter the exhaled breath, (2) covered with a Level 1 surgical mask, or (3) covered with a Level 3 surgical mask. Findings indicate that modifying EHMRs to filter the exhaled breath increases inspired CO2 levels, potentially increasing user discomfort but unlikely to cause serious physiological symptoms in healthy users, as all but one measurement was below 2%. Covering EHMR exhalation valves with surgical masks is unlikely to increase discomfort due to elevated inspired CO2 levels nor to cause serious physiological symptoms, as measurements were well below 2%. NIOSH's performance requirements provide an approval pathway for new EHMR designs without exhalation valves, which may be desirable when considering source control. In fact, while this study was in progress, several EHMR models without exhalation valves and an EHMR with a filtered exhalation valve accessory were approved. Since this study showed that modifying the EHMRs to filter the exhaled breath generally increased both exhalation resistance and inspired CO2 levels, and the magnitude of those increases varied among EHMR configurations, future research on the comfort and tolerability of new and modified EHMRs without exhalation valves needs to inform and improve designs appropriate for use in healthcare." - NIOSHTIC-2
  
  NIOSHTIC no. 20064300
  
  Suggested Citation: NIOSH [2022]. Evaluation of exhalation resistance and inspired carbon dioxide concentration in elastomeric half-mask respirators with modified or covered exhalation valves. By Strickland KT, Fernando R, Schall J, Walbert G, Brannen J. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2022-109. https://doi.org/10.26616/NIOSHPUB2022109
  
  2022-109.pdf?id=10.26616/NIOSHPUB2022109
  
  
• Subjects:
  Filtration Humidity Occupational Health Safety
• Series:
  NIOSH Numbered Publications
• DOI:
  https://doi.org/10.26616/NIOSHPUB2022109
• Document Type:
  Text
• Genre:
  Report
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  28 numbered pages
• NIOSHTIC Number:
  nn:20064300
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:053f7642b202d034e06eb6e9d43a247a86d606e7d5b735dbaa6b4b3c67c204ec2815641f6290b42620adab1d81529c80b557e88f74b54ee705c848c35ac3bb92
• Download URL:
  https://stacks.cdc.gov/view/cdc/113235/cdc_113235_DS1.pdf
• File Type:
  [PDF - 1.85 MB ]