Indian Journal of Critical Care Medicine

Register      Login



Volume / Issue

Online First

Related articles

VOLUME 25 , ISSUE 9 ( September, 2021 ) > List of Articles

Original Article

Prediction of N95 Respirator Fit from Fogging of Eyeglasses: A Pilot Study

Sandy Kyaw, Rimen Lim, Warren C Stewart, Natalia Rojas, Solomon R Thambiraj

Keywords : Eyeglasses, Healthcare workers, Infectious disease, Intensive care, N95 respirators, Occupational health

Citation Information : Kyaw S, Lim R, Stewart WC, Rojas N, Thambiraj SR. Prediction of N95 Respirator Fit from Fogging of Eyeglasses: A Pilot Study. Indian J Crit Care Med 2021; 25 (9):976-980.

DOI: 10.5005/jp-journals-10071-23947

License: CC BY-NC 4.0

Published Online: 08-09-2021

Copyright Statement:  Copyright © 2021; The Author(s).


Aim and objective: Fogging of eyeglasses while wearing N95 respirators is common. It is commonly held that the N95 respirator has a poor fit if there is fogging of eyeglasses. We conducted this prospective, pilot study to determine if fogging of eyeglasses predicts poor fit of N95 respirator. Materials and methods: Seventy volunteer healthcare workers from a tertiary intensive care unit in Sydney, Australia participated. The participants donned one of the following N95 respirators: three-panel flat-fold respirator (3M 1870), cup-shaped respirator (3M 1860), or a duckbill respirator. After a satisfactory “user seal check” as recommended by the manufacturer, the participants donned eyeglasses and checked for fogging. A quantitative fit test (QnFT) of the respirator was then performed (using PortaCount Respirator Fit Tester 8048, TSI Inc., Minnesota, USA). A fit factor of <100 on quantitative fit testing indicates poor fit. The sensitivity and specificity for fogging of eyeglasses (index test) to predict the poor fit of N95 respirator was determined, compared to QnFT (gold standard test). Results: Fogging of eyeglasses as a predictor of poor respirator fit (i.e., fit factor <100 on QnFT) had sensitivity of 71% (95% CI, 54–85%) and specificity 46% (95% CI, 29–63%). The odds ratio of fogging as a predictor for poor fit was 2.10 (95% CI, 0.78–5.67), with a two-tailed p-value of 0.22 (not significant). The receiver operating characteristic curve for fogging of eyeglasses as a diagnostic test had the area under the curve of 0.59. Conclusion: Fogging of eyeglasses is neither a sensitive nor a specific predictor for poor fit of N95 respirators.

  1. Sozkes S. COVID-19 and respiratory protection for healthcare providers. Int J Occup Med Environ Health 2021;34(2):307–318. DOI: 10.13075/ijomeh.1896.01666.
  2. Tirupathi R, Bharathidasan K, Palabindala V, Salim SA, Al-Tawfiq JA. Comprehensive review of mask utility and challenges during the COVID-19 pandemic. Infez Med 2020;28(Suppl. 1):57–63. Pubmed ID: 32532940.
  3. Haji JY, Subramaniam A, Kumar P, Ramanathan K, Rajamani A. State of personal protective equipment practice in Indian Intensive Care Units amidst COVID-19 pandemic: a nationwide survey. Indian J Crit Care Med 2020;24(9):809–816. DOI: 10.5005/jp-journals-10071-23550.
  4. Qian Y, Willeke K, Grinshpun SA, Donnelly J, Coffey CC. Performance of N95 respirators: filtration efficiency for airborne microbial and inert particles. Am Ind Hyg Assoc J 1998;59(2):128–132. DOI: 10.1080/15428119891010389.
  5. Australian Guidelines for the Prevention and Control of Infection in Healthcare. Canberra: Commonwealth of Australia, National Health and Medical Research Council (2019); 2019. Available from:
  6. Regli A, Sommerfield A, von Ungern-Sternberg BS. The role of fit testing N95/FFP2/FFP3 masks: a narrative review. Anaesthesia 2021;76(1):91–100. DOI: 10.1111/anae.15261.
  7. Lam SC, Lee JK, Yau SY, Charm CY. Sensitivity and specificity of the user-seal-check in determining the fit of N95 respirators. J Hosp Infect 2011;77(3):252–256. DOI: 10.1016/j.jhin.2010.09.034.
  8. Derrick JL, Chan YF, Gomersall CD, Lui SF. Predictive value of the user seal check in determining half-face respirator fit. J Hosp Infect 2005;59(2):152–155. DOI: 10.1016/j.jhin.2004.09.009.
  9. Kolewe EL, Stillman Z, Woodward IR, Fromen CA. Check the gap: facemask performance and exhaled aerosol distributions around the wearer. PLoS One 2020;15(12):e0243885. DOI: 10.1371/journal.pone.0243885.
  10. Chawla G, Abrol N, Kakkar K. Personal protective equipment: a Pandora's Box. Indian J Crit Care Med 2020;24(5):371–372. DOI: 10.5005/jp-journals-10071-23443.
  11. Choudhury A, Singh M, Khurana DK, Mustafi SM, Ganapathy U, Kumar A, et al. Physiological effects of N95 FFP and PPE in healthcare workers in COVID intensive care unit: a prospective cohort study. Indian J Crit Care Med 2020;24(12):1169–1173. DOI: 10.5005/jp-journals-10071-23671.
  12. PORTACOUNT RESPIRATOR FIT TESTER 8048 2021. Available from:
  13. Noti JD, Lindsley WG, Blachere FM, Cao G, Kashon ML, Thewlis RE, et al. Detection of infectious influenza virus in cough aerosols generated in a simulated patient examination room. Clin Infect Dis 2012;54(11):1569–1577. DOI: 10.1093/cid/cis237.
  14. OSHA. Fit testing procedures (Mandatory). Personal protective equipment. Occupational safety and health standards 2004.
  15. Respiratory protection–OSHA. Final rule; request for comment on paperwork requirements. Fed Regist 1998;63(5):1152–1300.
  16. Incorporated T. PORTACOUNT® PRO 8030 AND PORTACOUNT® PRO+ 8038 RESPIRATOR FIT TESTERS Revision P ed. TSI Incorporated / 500 Cardigan Road / Shoreview, MN 55126 / USA2015. p. 87-9.
  17. Clayton M, Vaughan N. Fit for purpose? The role of fit testing in respiratory protection. Ann Occup Hyg 2005;49(7):545–548. DOI: 10.1093/annhyg/mei046.
  18. Lei Z, Yang J, Zhuang Z, Roberge R. Simulation and evaluation of respirator faceseal leaks using computational fluid dynamics and infrared imaging. Ann Occup Hyg 2012;57(4):493–506. DOI: 10.1093/annhyg/mes085.
  19. Roberge RJ, Monaghan WD, Palmiero AJ, Shaffer R, Bergman MS. Infrared imaging for leak detection of N95 filtering facepiece respirators: a pilot study. Am J Ind Med 2011;54(8):628–636. DOI: 10.1002/ajim.20970.
  20. Peres D, Boleo-Tome JP, Santos G. Respiratory and facial protection: current perspectives in the context of the COVID-19 pandemic. Acta Med Port 2020;33(9):583–592. DOI: 10.20344/amp.14108.
  21. Williams DL, Kave B, Lee K, Segal R, Krieser RB, Mezzavia PM, et al. A randomised crossover study to compare the user seal check and quantitative fit test between two types of duckbill N95 particulate respirator masks: The Halyard Fluidshield® N95 and the BSN Medical ProShield® N-95 particulate respirator masks. Anaesth Intensive Care 2021;49(2):112–118. DOI: 10.1177/0310057X20974022.
  22. Kapoor A, Baronia AK, Azim A, Agarwal G, Prasad N, Mishra R, et al. Breathability and safety testing of personal protective equipment: “Human-comfort” factor remains undefined. Indian J Crit Care Med 2021;25(1):12–15. DOI: 10.5005/jp-journals-10071-23598.
  23. Lee K, Slavcev A, Nicas M. Respiratory protection against Mycobacterium tuberculosis: quantitative fit test outcomes for five type N95 filtering-facepiece respirators. J Occup Environ Hyg 2004;1(1):22–28. DOI: 10.1080/15459620490250026.
  24. Mainous AG, Hougland JG. Survey sampling issues in primary care research. Fam Med 1991;23(7):539–543. Pubmed ID: 1936737.
  25. Summers S. Selecting the sample for a research study. J Post Anesth Nurs 1991;6(5):355–358. Pubmed ID: 1833537.
  26. Wilkinson IJ, Pisaniello D, Ahmad J, Edwards S. Evaluation of a large-scale quantitative respirator-fit testing program for healthcare workers: survey results. Infect Control Hosp Epidemiol 2010;31(9):918–925. DOI: 10.1086/655460.
  27. Green S, Gani A, Bailey M, Brown O, Hing CB. An analysis on fit-testing of Respiratory Protective equipment in the UK during the initial response to the Covid-19 pandemic. J Hosp Infect 2021;113:180–186. DOI: 10.1016/j.jhin.2021.04.024.
PDF Share
PDF Share

© Jaypee Brothers Medical Publishers (P) LTD.