Assessing the Fit of N95 Filtering Facepiece Respirators Fitted with an Ear Loop Strap System: A Pilot Study (2025)

Abstract

Throughout the COVID-19 pandemic, hundreds of millions of people worldwide have become new users of respiratory protective devices. Facemasks and KN95 respirators utilizing an ear loop straps system (ELSS) have recently become popular among occupational and non-occupational populations. Part of this popularity is due to the ease of wearability as compared with traditional devices utilizing two headbands, one worn over the head and the other behind the neck—a universal strap system used in NIOSH-certified N95 filtering facepiece respirators (FFRs). Some users convert the two-strap configuration to an adjustable ELSS. The first objective of this pilot study was to quantitatively characterize how such a conversion impacts the respirator fit. Additionally, a novel faceseal (NFS) technology, which has been previously demonstrated to enhance the fit of N95 FFRs, was deployed to modify the ELSS-converted N95 FFRs. The second objective of this study was to quantify the fit improvement that results from adding the NFS to the ELSS. The study was conducted by performing the Occupational Safety and Health Administration (OSHA)-approved quantitative fit testing (QNFT) on 16 human subjects featuring different facial shapes and dimensions. Three models of cup-shaped N95 FFRs were tested in three versions: the standard version with manufacturer’s strap system, the ELSS-converted, and the ELSS-converted version modified by adding the NFS. QNFT demonstrated that the fit of an N95 FFR featuring the traditional/standard headbands strap system is negatively impacted when this system is converted to an ELSS. The fit of an ELSS-converted respirator can be significantly improved by the addition of the NFS. We found that the FFR model and the strap system version are significant factors affecting the QNFT-determined respirator fit factor (FF), as well as the OSHA QNFT pass rate (FF ≥100). The findings suggest that the current NFS, if further improved, has a potential for developing a ‘universally fitting’ ELSS-equipped N95 FFR that can be used by the general public, the vast majority of whom do not have access to OSHA fit requirements.

What’s important about this paper.

Increased use of facemarks and respirators during the COVID-19 pandemic led to the exploration of alternative designs by the public, including changing the two head straps into ear loop straps. This study found that the modification to ear loop straps decreases the fit of N95 filtering facepiece respirators, but that the addition of a novel faceseal technology can improve the fit factor of the modified respirators. Further development is needed, but the designs tested in this study suggest a path towards a ‘universally fitting’ device for public use.

Introduction

As a result of respiratory protection protocols adopted worldwide during the COVID-19 pandemic, hundreds of millions of people—many of whom had not used respiratory protection routinely—began wearing a wide variety of respiratory devices on a daily basis. Many of these were low-efficiency cloth masks or face coverings, while others, such as NIOSH-approved filtering facepiece respirators (FFRs) offered a significantly higher level of protection for a wearer (Grinshpun et al., 2009; Reutman et al., 2021; CDC, 2022). NIOSH-certified N95 FFRs were in severely short supply during the early phases of the pandemic, and as such it was advised that they be restricted to occupations in the highest risk categories, being primarily in healthcare. In a number of occupational settings, OSHA fit testing was required, and available, to employees.

In the January of 2022, the CDC updated their standards for respiratory protection for the general public, recommending the use of N95 FFRs as the highest level of protection against virus aerosol pathogens—including COVID-19 (CDC, 2022). Simultaneously, the US government dispensed 400 million N95 respirators to be available to the public, without charge, at pharmacies and community health centers. These latest efforts present challenges associated with differences in the public awareness and compliance. N95 FFRs require fit testing to ensure that the wearer has an expected level of protection. In the US, these tests follow OSHA’s 29CFR1910.134 protocol.

However, it is unlikely that the general public—the vast majority of whom are not employed in an occupation requiring employer-provided respiratory protection—will have knowledge of an OSHA fit test, nor where to seek an OSHA fit testing facility. The general public may not fully understand how the individual choices of the models and sizes of respiratory protective devices relate to the face dimensions of a specific wearer. Most internet-based purchasing sites offer the ‘regular’ size first, with a smaller size offered only through further searching. On-site retail stores seldom offer anything but the ‘regular’ size, or ‘Medium/Large’ versions. Finally, a significant number of manufacturers offer only ‘one size fits all’ masks.

Another issue is ease of donning and doffing of the facemasks/respirators. Essentially, all NIOSH-approved FFRs marketed in the US are designed with two headbands, one worn over the head and the other behind the neck. In contrast, virtually all facemasks, and K95-style respirators, utilize an ear loop strap system (ELSS) to secure the mask to the user’s face. However, headband-designed respirators present challenges for the wearers. As an example, female healthcare workers often find the traditional two-strap design problematic as the strap over their head can disrupt, or be disrupted by their hair configuration, which can then cause changes in the head strap’s tension and thereby potentially in the respirator fit. It has been reported by the Centers for Disease Control and Prevention (CDC, 2021) that masks and respirators using an ELSS, e.g. KN95, are becoming popular among occupational and non-occupational populations because they are more comfortable to wear. Therefore, users sometimes convert the traditional two-strap headband design to an adjustable ELSS.

Recent studies looking at compliance with wearing facemasks/respirators, has substantiated that if given the choice, the public would still be more inclined to buy a cloth mask or K95 FFR with ELSS, rather than an N95 (Ritter and Brenan, 2020; The Economist, 2020; Morning Consult, 2022).

There is a lack of data regarding the effect of this conversion on the respirator fit. As the fit is conventionally quantified by performing the OSHA-approved quantitative fit testing (QNFT) on human subjects, the first objective of this pilot study was to quantitatively characterize how the ELSS configuration impacts the fit factor (FF) and the QNFT pass rate (FF ≥100) of an N95 respirator.

Additionally, the University of Cincinnatis bjects subjectsectsuantitative fit tefaceseal (NFS) technology developed and patented by one of the authors of this paper (RK). The application of this technology to N95 FFRs has been demonstrated to significantly increase the FF of an N95 FFR (Koehler et al., 2014; Grinshpun et al., 2020). The NFS design is based upon critical zones in human facial anatomy where leakage has been shown to be most likely to occur (Oestenstad et al., 1990; Roberge et al., 2011; Lei et al., 2013). The key element of this technology is an ethylene vinyl acetate (EVA) foam that is secured to the inner perimeter of the respirator, enhancing its fit to the user’s face. In this effort, we applied the new faceseal to the ELSS-configured N95 FFRs and evaluated the modified respirators through the above-mentioned QNFT. Thus, the second objective of this study was to quantify how the respirator fit is affected by adding the faceseal to the ELSS-configured N95 FFRs.

Methods

Results

Discussion

The results of this pilot study suggest that the conversion from the standard two-strap respirator version to the ELSS configuration, which aims at improving wearability and comfort, may negatively impact the performance of an N95 FFR (two of three models showed such a trend for the pass rate). This may be attributed to the fact that the two ear loop straps, which comprise the ELSS used herein, are less capable of assuring sufficient tightness (as compared with the standard version). Although the ELSS was made adjustable in this study, this strap configuration did not achieve a sufficiently tight seal between the respirator’s facepiece and the wearer’s face resulting in lower FF values. This finding is consistent with the results reported on the fit of masks, virtually all of which feature ear loop straps (Mottay et al., 2021; Yung et al., 2021). Among them, Mottay et al. (2021) evaluated the seal, fit and filtration efficiency of several KN95 masks with ear loop designs, and found that the tested masks failed the stipulated safety thresholds. Yung et al. (2021) also found that masks with ear loops had much lower efficiency than those with headbands. Additionally, our data are in agreement with the results reported by Caoili et al. (2020), who found a high failure rate (39 failures out of 42 fit tests) of KN95 vertical-fold shaped masks with the ear loop design.

It is noted that FFs measured for the standard and the ELSS + NFS versions were not significantly different for Honeywell DC365 and 3M 1860 models. However, this study was designed to address only on two comparisons: Standard versus ELSS and ELSS versus ELSS + NFS.

The outcome of this study—a documented improvement of the performance of ELSS-configured N95 FFRs due to the faceseal technology—is in line with our earlier findings (Koehler et al., 2014; Grinshpun et al., 2020). While all the tested subjects wearing the standard Makrite 9500 and almost all tested subjects wearing the ELSS version (15 of 16) failed the fit test, yet, with the faceseal added to the ELSS version, half of the subjects passed the fit test. The face dimensions of the test subjects who passed the fit testing were concentrated in zones 4, 5, 6, 7, and 9 of the NIOSH bivariate panel. A similar trend was observed for the other two respirator models. This finding corroborates that the QNFT pass rate is influenced by the face dimensions. The tested subjects whose facial dimensions represent zones 2 and 3 of the NIOSH panel achieved lower pass rates, even when the faceseal was applied. This reflects limitations that obviously exist for subjects with small faces in achieving a tight fit with the regular size respirators even in the presence of the faceseal enhancement. Since in this pilot study we did not perform fit testing on respirators with small size, a follow-up investigation covering subjects with small faces and respirators of different sizes is called for.

In 2020, the American Society for Testing and Materials (ASTM) developed the ASTM F3407-20 voluntary standard for respirator manufacturers, which proposed a minimum QNFT pass rate for 25 subjects wearing N95 FFRs being 13 out of 25, i.e. slightly in excess of 50% (ASTM, 2020). Our data show that by applying the faceseal technology to the ELSS versions of the three N95 FFRs that we tested, two of three models would produce a pass rate of 50% or greater and the third model would be close to that. Therefore, we believe that this technology, if further improved, has a potential for developing a ‘universally fitting’ N95 FFR with ELSS that can be used in various occupational environments as well as by the general public. In the event of a major pandemic, potential users in the general public will likely be selecting a N95 FFR at random with limited knowledge of judging an adequate fit. Furthermore, the universal availability of OSHA fit testing equipment for hundreds of millions of users appears highly unrealistic. Therefore, the findings of this study are significant for getting FFRs meeting the ASTM-proposed standard to the general public.

We acknowledge that the NFS used herein represents a first stage design, which was tested for a concept evaluation only. At this point, it is in no way suggested that the new respirators be submitted for NIOSH certification. Likewise, it is in no way proposed that the modifications made in the study protocol be construed as suggesting that the respirator wearers should try to modify an existing NIOSH-approved N95 FFR with the NFS or alter it with the ELSS.

Conclusions

The fit of an N95 FFR featuring the standard strap system may be negatively impacted when this system is converted to the ELSS format. At the same time, the fit of an ELSS-converted respirator can be significantly improved by the addition of the novel faceseal technology. The FFR model and design were found to be significant factors in affecting the fit as quantified by the outcomes such as the FF value and the QNFT pass rate. We believe that the faceseal concept provides the foundation for the development of a ‘universally fitting’ ELSS-configured N95 FFR, which can be used by workers as well as by the general public. This is an important benefit considering that it would be immensely difficult, if not impossible, to implement and administer a mandatory respirator fit testing program for the general public, who will be choosing an N95 largely by random selection.

As a follow-up on this pilot research, a more extensive testing of the faceseal technology will be performed to address a greater and more diverse study population, involve different shapes and sizes of respirators and, possibly, examine other variables.

Contributor Information

Xinyi Niu, Center for Health-Related Aerosol Studies, Department of Environmental and Public Health Sciences, University of Cincinnati, Cincinnati, OH, USA.

Richard H Koehler, Critical Fit Technologies LLC, Tisbury, MA, USA.

Michael Yermakov, Center for Health-Related Aerosol Studies, Department of Environmental and Public Health Sciences, University of Cincinnati, Cincinnati, OH, USA.

Sergey A Grinshpun, Center for Health-Related Aerosol Studies, Department of Environmental and Public Health Sciences, University of Cincinnati, Cincinnati, OH, USA.

Funding

This effort was partially supported by the National Institute for Occupational Safety and Health, grant 1 R01-OH011947. The authors are grateful for this support.

Conflict of interest

The authors declare no conflicts of interest relating to the material presented in this article. It is disclosed that one of the authors (R.H.K.) holds a US Patent on the faceseal technology used in this study; however, his invention has not been either licensed or commercialized. The paper contents, including any opinions and/or conclusions expressed, are solely those of the authors.

Data availability

The original data that support the findings of this study are available from the corresponding authors [sergey.grinshpun@uc.edu] upon request.

References

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