Advancements in Elastomeric Respirator Technology for Use as Source Control

Posted on by Rohan Fernando, M.S; Jeffrey Peterson; and Lee Portnoff, M.S
Photo courtesy of NIOSH NPPTL: Prototype design of filter adaptor developed by NIOSH

Respirator design is constantly improving and evolving to meet new challenges. Manufacturers have recently developed innovative NIOSH-approved elastomeric half mask respirator (EHMR) designs that both protect the wearer as well as provide adequate source control – protecting others by filtering the wearer’s exhaled air that may contain harmful viruses or bacteria.

EHMRs are being used more widely in U.S. healthcare systems because they can be cleaned, disinfected, and reused. During times when there are shortages of the filtering facepiece respirators (FFRs) typically worn in healthcare settings, EHMRs can help to meet this demand and alleviate the burden on the FFR supply. However, EHMRs traditionally have exhalation valves, which is a design feature that has caused concern about source control.

A respirator’s exhalation valve works by closing when the wearer inhales, pulling the inhaled breath through the filter material, and then opening to allow exhaled unfiltered breath to be expelled through the exhalation valve. This helps to reduce the overall breathing resistance, remove moisture, and reduce CO2 concentration and its effects, thereby increasing the user’s comfort, especially over a long period of time. A NIOSH-approved particulate respirator with an exhalation valve offers the same intended protection to the wearer as one without a valve. However, potential respiratory droplets expelled by wearers may exit along with air through the exhalation valve, which means that they may not provide efficient source control for use in certain healthcare settings, such as those requiring a sterile field. This limits how much traditional EHMRs with exhalation valves can be incorporated into healthcare systems to alleviate the supply shortage of FFRs.

Several NIOSH respirator approval holders have tackled this source control dilemma, developing new EHMR options that can both protect healthcare workers and be used in all healthcare settings. NIOSH has recently approved the first EHMR model without an exhalation valve. The Mine Safety Appliance Corporation (MSA) designed the Advantage 290, which provides P95 and P100 level protection to the wearer, as well as reduces the risk of spreading infectious diseases through expelled droplets in exhaled breath. This is because the air is being filtered in both directions. The lack of open exhalation valve forces the exhaled breath of air back out the same filter in which the air was breathed in.

Since this first approval, NIOSH also issued approval for Dentec Safety Specialists’ 400 NX series half mask respirators without exhalation valves. This includes the 400NXML, 400NXMDML, 400NXSM, and 400NXMDSM.

The 3M Corporation took a different approach to reduce the spread of infectious disease through respirators that have exhalation valves. 3M now offers an accessory filter that can be installed over the exhalation valve on their 6000 series of particulate-filtering EHMRs. This accessory filters the exhaled breath that passes through the exhalation valve. NIOSH has accepted this filter accessory as part of the approved 6000 model series respirator configuration. Its filtered exhalation valve provides source control similar to medical masks which are the products typically used in healthcare for source control.


NIOSH’S Contribution to the Science

In addition to the role of testing and certifying the effectiveness of these respirators for occupational use, NIOSH is contributing to the body of scientific knowledge in this area and fulfilling critical research needs to determine the potential for respirators with exhalation valve to be used as source control.

Exhaled Breath Filter Adaptors for Commercial Respirators

Based on their prevalent use in healthcare and a need to better understand the source control performance of EHMRs, NIOSH researchers used EHMR models from Honeywell International Inc., 3M, and MSA for a study on exhaled breath filter adaptors. This study was initiated to understand the effects of blocking an exhalation valve and directing the exhaled air back through the main (inhalation) filters, or, alternately, covering the exhalation valves externally with a surgical mask. The results from the study demonstrated that these EHMRs can be modified by blocking the exhalation valve and redirecting the exhaled breath though the main filters and still meet the NIOSH exhalation resistance performance requirement. However, there were increases in both the exhalation resistance and CO2 levels within the facepiece caused by modifying the respirators to filter the exhaled breath. NIOSH is working on designing and fabricating prototype filter housing adapters for select commercially available respirators with consideration to minimize any increases in exhalation resistance or CO2 concentrations inside these EHMRs.

Reusable Healthcare EHMRs

The objective of this project is to design and produce prototypes of reusable EHMRs specifically designed for healthcare delivery settings, meeting the specific needs of healthcare workers. The project commenced with input from stakeholders and examined the required features desired by healthcare workers in order to determine the best design direction. These respirators will consist of a half mask body incorporating an exhalation valve, filter attachment ports, and possibly a speech diaphragm. Based on the reported needs of healthcare workers, this respirator type must be low profile, ergonomically designed to allow the user a wide field of vision, have a comfortable head harness that is simple to put on, and be easily cleaned for reuse. It would incorporate an N95 particulate filter that would be discarded after use.

See the NIOSH NPPTL website for more information about NIOSH respirator exhalation valve research.


Rohan Fernando, M.S., is a Mechanical Engineer within the Research Branch of the NIOSH National Personal Protective Technology Laboratory.

Jeffrey Peterson is the Branch Chief of the Conformity Verification and Standards Development Branch in the NIOSH National Personal Protective Technology Laboratory.

Lee Portnoff, M.S., is a Biologist within the Research Branch of the NIOSH National Personal Protective Technology Laboratory.


Mention of any company, product, or service is for informational purposes only and does not constitute endorsement by the National Institute for Occupational Safety and Health (NIOSH), the Centers for Disease Control and Prevention (CDC), or the U.S. Department of Health and Human Services (HHS), or imply that any company or its products or services are preferred over any other.

Posted on by Rohan Fernando, M.S; Jeffrey Peterson; and Lee Portnoff, M.S

11 comments on “Advancements in Elastomeric Respirator Technology for Use as Source Control”

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    When the exhalation valve is blocked, along with the increase in breathing resistance and CO2 levels comes an increase in accumulated moisture that will leak out profusely through the front of the mask or it will require the user to remove the mask to pour out the accumulated moisture.

    If prolonged use of a NIOSH approved elastomeric respirator without an exhalation valve or with the valve covered causes the wearer discomfort due to increases in CO2 levels, breathing resistance and moisture levels, the user can alleviate this discomfort by periodically leaving the area where respiratory protection is required and removing the respirator for a short duration. Prior to going around others or re-entering the area where respiratory protection is required, the respirator must be re-donned in accordance with the manufacturer’s user instructions. Issues encountered with discomfort should be reported to the site’s respiratory protection program manager.

    Respirator manufacturers need to address the problem of masks loosening when the user looks down and over-tightening when the user looks up. This is either uncomfortable, if the strap is tight enough when looking down, or dangerous, if the strap is loose enough when looking up. There should be no neck strap. All the straps should be on the skull. That way the dimensions won’t change no matter how low or high the users tilt their heads.
    I have modified my Honeywell 7700 respirator by running a short string from the head harness down to the “neck strap” buckle. The string pulls the buckle up to right where my neck joins my skull.
    When I tilt my head the mask stays at the right tension.
    Note: I am retired and wear my respirator when I go out to protect me from covid so I am not breaking NIOSH’s/OSHA’s rules by modifying my respirator.

    Thank you for your comment. You are correct that the manufacturer’s user instructions must be followed in order to use the product in a NIOSH-approved configuration. Modifications to the respirator outside the approved configuration voids the NIOSH approval.

    I found the 3M 6000 series exhalation valve filter advertised on the website of a safety supplier, and ordered some, a box of 5, I believe. They are back ordered with an unknown time of availability. Not a surprise, I guess. For my personal use, only, I sealed the exhalation valve of a half mask, and removed the inhalation valve flappers to permit exhalation through the filters. I don’t find resistance substantially increased, but humidity is a big issue. This respirator has P100 cartridges on it. I don’t have information on changes in efficiency or resistance of the cartridge which might result from exhalation through those cartridges of saturated air, though as 100-class, they could lose some and still be acceptable. Maybe. How would you quantify outside a lab? Some (many?) activities will not allow respirators with exhalation valves even if sealed, for example clinics, or a major US airline. The exhalation filter seems a good solution, if ever available.

    As part of ongoing studies at NIOSH, sealing the exhalation valve of a elastomeric half mask respirator, and removing the inhalation valve flappers to permit exhalation through the filters was investigated in addition to studies with other modifications. Publication of the results of these studies is forthcoming. It would be difficult quantify such parameters objectively outside a laboratory setting.

    Did the NIOSH study about filtration efficacy changes without an exhalation valve ever get released?

    Filtration efficacy changes without an exhalation valve was evaluated by NIOSH. The publication of the results from these evaluations is forthcoming.

    I worked on a project with faculty from the U.S. Naval Academy and UCSF Epidemiology Dept that I think meets these requirement, plus a few more:

    – Exhale filtration
    – Optically clear face
    – Silicone Face seal
    – Cool and bone-dry inside (I recorded a video of a wearer deliberately hyperventilating and the mask still stays dry.)
    – Easily accommodates eyewear (even crazy things like an ophthalmoscope)
    – Uses its own brand of filters or 3M and Honeywell filters

    Would love to demonstrate it to anyone interested at CDC/NIOSH…

    I bought the [product name removed] respirator and wore it for about an hour. It was quite comfortable yet a little steamy when I was outside on a Summer day. This seems to be an excellent tradeoff when it provides very excellent (P100 level?) source control.

    Do these NIOSH approved unvalved elastomeric respirators provide source control at least equal to that of medical masks? Are they as good for source control as surgical masks?

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Page last reviewed: March 1, 2021
Page last updated: March 1, 2021