Considerations for Covering N95s to Extend Use

Introduction

During times of increased demand for N95 filtering facepiece respirators (FFRs), hospitals or other medical facilities may want to protect these devices from surface contamination in order to prolong their use. When protection against surface contamination is needed, CDC recommends wearing a cleanable face shield over an N95 FFR^[1]. Wearing a surgical mask or cloth covering over an FFR, such as an N95, is not approved or recommended by NIOSH because it is not consistent with the conditions of the approval, therefore voiding the certification, however this is a strategy that can be used in a crisis situation as described in the CDC strategies for Optimizing the Supply of N95 Respirators. *

This blog does not address exhalation valves and the impact of an asymptomatic respirator wearer (i.e. protection from contaminated breath from asymptomatic wearers). Instead, this blog addresses the use of coverings as a means to provide protection from surface contamination.

While wearing a covering over an N95 is not consistent with the condition of the approval, several studies have been conducted on the effects of wearing a surgical mask over an N95. This blog summarizes the available research on covering N95s when such practices are considered as part of a crisis strategy (i.e., as a last resort). Note that the effect of any coverings on N95 respirator filtration, fit, or comfort over a prolonged period has not been explored within the available research; therefore, NIOSH cannot provide specific recommendations for the use of these coverings.

National Academy of Medicine Study (Formerly the Institute of Medicine)

In a study conducted in 2006, the Institute of Medicine (IOM) considered the potential for limited reuse of N95s in the event of an influenza pandemic. In the study, the IOM recommended that the concurrent use of a surgical mask worn as an outer barrier, or a washable faceshield, could potentially extend the useful life of an N95 by acting as a physical barrier to potentially infectious liquids and droplets, as well as block larger particles (1). This recommendation was made to allow for only limited reuse of N95s, and the specific amount of time that this covering may extend use of an N95 is not known. The use of a cloth (non-surgical) mask covering to extend the life of an N95 was not examined by the Institute of Medicine. Covering an N95 mask with either a cloth or surgical mask is not recommended by NIOSH.

 

NIOSH Studies on Covering an N95 with a Surgical Mask

NIOSH has conducted two studies looking into the impact of covering N95 respirators with surgical masks. The first study in 2010 found that healthcare worker use of a surgical mask as an outer barrier over a cup-style N95 FFR did not significantly impact the wearer’s physiological burden or perception of comfort and exertion over a 1-hour period. Study participants walked on a treadmill to simulate less strenuous and more strenuous work rates. No significant differences were found in blood carbon dioxide, measured by a sensor worn on the ear, or in the levels of carbon dioxide present in the area inside the respirator. The study also revealed no significant difference in moisture gain (added moisture due to breathing) by the respirator when covered with a surgical mask. This is important because moisture gain can theoretically result in increased breathing resistance (making it harder to breathe), which would negatively impact the user by increasing respiratory rate, tidal volume (the air displaced between normal inhalation and exhalation), and heart rate (2).

The second study, published in 2012, simulated breathing while wearing 30 different N95 models with and without a surgical mask covering for six different workloads. The results showed that for the less strenuous workloads (workloads for activities such as desk work used for writing patient notes), adding a surgical mask over an N95 had a minimal effect on physical work performance. The differences among inhaled oxygen, carbon dioxide, and breathing resistance from a surgical mask placed over an N95 compared to an N95 alone likely would be imperceptible by the wearer over short wear durations (3). However, the impact of this covering in extended use or reuse situations has not been examined by NIOSH.

Filter efficiency is another important area of consideration. Aerosol filter efficiency is not expected to be affected by the addition of a secondary barrier provided by a covering. A NIOSH comparison of FDA-cleared surgical N95s (N95s that resist penetration by high-pressure streams of liquid) and N95s without fluid resistance found similar levels of performance in the areas tested using FDA test methods. (5).

Finally, in order to provide adequate protection, an N95 must be fit properly to the wearer. The impact of wearing a surgical mask or cloth mask over an N95 on the ability of the N95 to seal properly with the face is not well studied. Any change in breathing pressure may lead to leaks where the N95 should form a seal against the skin, and any mask barrier fabric or straps may interfere with proper fit of the N95 (4). The effect on wearer comfort or potential skin irritation is also not known.

 

Caution Moving Forward

Protecting an N95 from surface contamination may be achieved by wearing a cleanable face shield over an N95 instead of covering it with a mask. However, if a facility is considering using surgical or cloth mask coverings as a last resort during a crisis strategy, care should be taken to ensure that the fit and function of the N95 respirators are not negatively impacted. Additionally, employers, respiratory protection program administrators, and respirator users should understand that liquids and aerosols not filtered by a surgical mask (or other covering) may be present on the outer surface of an N95. This is true whether a face shield or mask is used. As such, the N95 should be handled as if the outside is contaminated by the environmental hazards (aerosols or fluids), despite the covering.

NIOSH recommends that a facility’s respiratory protection program administrators consider consulting respirator manufacturer and infectious disease specialists about additional training for staff to reinforce the need to minimize unnecessary contact with the respirator surface, and for strict adherence to hand hygiene practices, and proper personal protective equipment (PPE) donning and doffing technique^[2].

Whether and how an employer decides to implement specific crisis strategies should be based on present and projected risk mitigation needs and local, regional, and national availability of N95s.

This summary of available research should not be read as an endorsement or recommendation for covering an N95 with a surgical or cloth mask. The recommended practice is the use of a cleanable face shield worn over the N95.

 

Jeffrey Powell, MS, is a biologist in the NIOSH National Personal Protective Technology Laboratory Research Branch.

Jonisha Pollard, MS, CPE, is a team leader in the NIOSH National Personal Protective Technology Laboratory Research Branch.

Dana Rottach, PhD, is a Physical Scientist in the NIOSH National Personal Protective Technology Laboratory Research Branch.

Edward Sinkule, PhD, MPH, FACSM, is Physical Scientist in the NIOSH National Personal Protective Technology Laboratory Research Branch.

* Edit made for clarity

 

 

References

1. Institute of Medicine. Use and Reuse of Respiratory Protective Devices for the Influenza Control. In: Bailar III JC, Burke DS (eds) Reusability of Facemasks During an Influenza Pandemic: Facing the Flu. The National Academies Press, Washington, 2006; 16–17. https://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=s04272006
2. Roberge, R.J., Coca, A., Williams, W.J., Palmiero, A.J. and Powell, J.B. (2010), Surgical mask placement over N95 filtering facepiece respirators: Physiological effects on healthcare workers. Respirology, 15: 516-521. doi: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1440-1843.2010.01713.x
3. Edward James Sinkule, Jeffrey Bryon Powell, Fredric Lee Goss, Evaluation of N95 Respirator Use with a Surgical Mask Cover: Effects on Breathing Resistance and Inhaled Carbon Dioxide, The Annals of Occupational Hygiene, Volume 57, Issue 3, April 2013, Pages 384–398, https://doi.org/10.1093/annhyg/mes068
4. Thomas J. Nelson & Craig E. Colton (2000) The Effect of Inhalation Resistance on Facepiece Leakage, AIHAJ – American Industrial Hygiene Association, 61:1, 102-105, DOI: 10.1080/15298660008984522
5. Samy Rengasamy, Ronald Shaffer, Brandon Williams & Sarah Smit (2017) A comparison of facemask and respirator filtration test methods, Journal of Occupational and Environmental Hygiene, 14:2, 92-103, DOI: 10.1080/15459624.2016.1225157

[1] Recommended Guidance for Extended Use and Limited Reuse of N95 Filtering Facepiece Respirators in Healthcare Settings, https://www.cdc.gov/niosh/topics/hcwcontrols/recommendedguidanceextuse.html

[2] CDC: “Sequence for donning personal protective equipment PPE/Sequence for removing personal protective equipment.” [Online] Available at https://www.cdc.gov/HAI/pdfs/ppe/ppeposter148.pdf