Abhijay,

I will try to address your first question by way of some background. 

Since the SARS outbreak in 2003, there has been questions about the effectiveness of N-95 respirators during the SARS Epidemic in Hong Kong, China and Canada and relying on fit-tested N95 respirators during an Avian Influenza epidemic. I actually spoke about the issue at the 2007 AOHC and 2007 AIHce Meetings in my talk on Infectious Aerosols.

The issue is:

FDA

FDA certifies material used in respirators.  For example A respirator’s Nominal Protection Factor (NPF) is the theoretical protection level based on laboratory measured performance data.  That said the Assigned Protection Factor (APF) is the level of respiratory protection that can realistically be achieved in the workplace by 95% of adequately trained and supervised wearers.  Consequently, the APF should be used when selecting a respirator.

NIOSH

NIOSH certifies respirators and require that Bacterial Filtration Efficiency be the standard test method for Medical Face Mask material (ASTM F2101-01).  The procedure for a NIOSH N95 certification is available at the following website address: http://www.cdc.gov/niosh/npptl/resources/certpgmspt/default.html . They include four components: 1) filtration efficiency; 2) inhalation resistance; 3) exhalation resistance, and 4) exhalation valve leak (when applicable).

NIOSH Standard: Neutralized NaCl aerosol: a median mass diameter of 0.26µ (0.075± 0.02µ)

Other standards used to screen new respirator material (as per Military Specification MIL-STD 36954C)

Bacterial Filtration Efficiency (BFE) Aerosol of Staphylococcus aureus with a MPS of approximately 3.0µ.

Viral Filtration Efficiency (VFE) phiX174 bacteriophage at 0.027µ  (27 nm) in size (one of the smallest known viruses, has no envelope, and has icosahedral morphology)

OSHA

OSHA requires that respirator user must adhere to program requires in OSHA’s Respiratory Protection Standard (29 CFR 1910.134) and used in their approved configuration (Fit Testing) to achieve the assigned Protection Factor  (APF)  for the particulate respirator (which is multiple of the permissible exposure limit (PEL)  for the hazardous agent in question.

OSHA 42 CFR Part 11 Standard certifies the N-95 respirator filtration efficiency using the most penetrating aerosol size  (0.30 µ) with either degrading or non-degrading particulates to challenge the respirator at 95, 99, or 99.97% filtration efficiency.

Note: An N-95 respirator is one of nine types of disposable particulate respirators.

Particulate respirators are also known as “air-purifying respirators” because they protect by filtering particles out of the air as you breathe. These respirators protect only against particles—not gases or vapors. Since airborne biological agents such as bacteria or viruses are particles, they can be filtered by particulate respirators.

Respirators in this family are rated for protection against oils.

This rating is important in industry because some industrial oils can degrade the filter performance so it doesn’t filter properly.* Respirators are rated “N,” if they are not resistant to oil, “R” if somewhat resistant to oil, and “P” if strongly resistant (oil proof). Thus, there are nine types of disposable particulate respirators:

    N-95, N-99, and N-100

    R-95, R-99, and R-100

    P-95, P-99, and P-100

Those that filter out at least 99% receive a “99” rating. And those that filter at least 99.97% (essentially 100%) receive a “100” rating.

The N-series will be tested against a mildly degrading aerosol of sodium chloride (NaCl). The R- and P-series filters will be tested against a highly degrading aerosol of dioctylphthalate (DOP)

Those that filter out at least 99% receive a “99” rating. And those that filter at least 99.97% (essentially 100%) receive a “100” rating.

The N-series will be tested against a mildly degrading aerosol of sodium chloride (NaCl). The R- and P-series filters will be tested against a highly degrading aerosol of dioctylphthalate (DOP)

The N95 designation indicates that under the test methods in the laboratory, 95% of particles are captured with a GMD (Geometric Mean Diameter) of 1.6 micron (or 5% will pass through).

Face seal leakage in N95 respirators can be estimated at 1% when properly fit tested. This value corresponds to a fit factor of 100, which is OSHA’s criterion for an acceptable fit.

This is in addition to the large leakage that will result in the practical environment where face fit is not possible and where no training in respiratory protection has been carried out.

A NIOSH certified N-95 rated respirator will filters out at least  95% of airborne particles during a 0.3 micron sized particle challenge.

Note: Other respirators (e.g surgical mask) are allowed to transmit greater than 20% particles through the respirator, but in practice much greater leakage of particles will result due to face fit factors

Consequently, the assigned protection factors (APF)  are only effective when the employer

implements a continuing, effective respirator program as required by OSHA (29 CFR 1910.134), including training, fit testing, maintenance, and use requirements. ( NIOSH Pub. No. 2005-100 (Oct 2004)      

Finally, the main problem in 2007 was the number of competing standards for respiratory protection which created a challenge in the containment of infectious aerosols as summarized below:

ACGIH TLV’s    vs  OSHA Limits       (Air Quality)

ACGIH TLV's    vs NIOSH REL's       (Safe Level)

ACGIH       vs DOE    (Falling efficiency)

CDC Biohazard    vs Animal Biosafety (NHP)

Res. Laboratory   vs Hospital             (BBP)

JCAHO        vs  OSHA             (Tbc)

Note: OSHA Rescinded their own OSHA Guidelines for Tuberculosis in 1995 (based on the realization that the standard would not prevent its most common method of transmission (i.e. undetected reactivation of disease)

OSHA          vs  EPA     (Katrina Relief)

ASHRAE     vs  FAA                       (A/C Cabin)

ASHRAE     vs  CDC               (ACH)

ICPA        vs     OSHA (standard of care issues)

AOHN        vs  CDC (fit testing)

So, that is why there is finally a MOU (10 years later) between NIOSH, FDA, and OSHA (Memorandum of Understanding Between the Food & Drug Administration/Center for Devices & Radiological Health and the Centers For Disease Control & Prevention/National Institute for Occupational Safety & Health/National Personal Protective Technology Laboratory)  https://www.fda.gov/about-fda/domestic-mous/mou-225-18-006

Consequently, you can use either a N-, R-, or P- respirator while caring for COVID-19 patients as long as you have been successfully fit-tested on the respirator.

I hope this is helpful.

Michael

Michael A. Sauri, MD, MPH&TM, FACP,

FACPM, FACOEM, FRSTM&H, CTropMed

Medical Director

Occupational Health Consultants

2301 Research Blvd, Suite #125

Rockville, MD 20850

Tel 301-738-6420

Fax 301-990-3534

www.ohcmd.com