Lisa M Brosseau, ScD, CIH

• Dr. Brosseau, now retired, was a Professor at the University of Illinois Chicago, where she led two NIOSH centers: the Illinois Education and Research Center and the UIC Center for Public Health. She now works as a part-time consultant for the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota.

• Dr. Brosseau is a certified industrial hygienist with a long academic research career specializing in respiratory protection, with particular attention to healthcare and infectious aerosol exposures. She has more than 100 peer-reviewed publications and book chapters and has written several articles for the CIDRAP website. She has been consulting with unions, companies and individuals and delivering webinars throughout the COVID-19 pandemic.

• Personal website: lisabrosseau.com

Face CoveringsSurgical MasksRespirators

Lisa M Brosseau, ScD, CIH

Professor (retired)

Research Consultant, University of Minnesota, Center for Infectious Disease Research and Policy (CIDRAP)

What are they?Face Coverings

• Mostly made of cloth (woven material)

• No standards or testing

• CDC: 2 layers over nose & mouth; fit snugly against face

• New ASTM barrier face covering standard (published Feb 2021)

Surgical Masks• Some are “Cleared for marketing”

by FDA – 3rd party testing; FDA does not test

• Defined as “covers the user’s nose and mouth and provides a physical barrier to fluids and particulate materials.”

• Includes masks labeled as surgical, laser, isolation, dental or medical procedure masks with or without a face shield.

• Masks for use during surgical procedures. Most masks in healthcare settings are not FDA-cleared.

• Tests for filter efficiency, pressure drop, fluid resistance & flammability

Respirators

• Certified by NIOSH

• Tests for filter efficiency, breathing resistance, loading, oil aerosols, fit (gas/vapor only)

• Periodic evaluations of quality control

• OSHA requires annual fit testing for every employee

Surgical N95 Respirator• Worn to protect both the

patient and worker• Approved by NIOSH & cleared

for marketing by FDA

https://www.fda.gov/regulatory-information/search-fda-guidance-documents/surgical-masks-premarket-notification-510k-submissions

FacepiecePerformance Depends On…

Filter efficiency - How well does the filter collect airborne particles?

Airflow resistance – How hard is it to breathe through the filter?

Fit - How well does the facepiece prevent leakage of contaminants?

Proper use - Proper donning and checking the seal may influence performance

Filter Testing

Use

Worst case test conditions

- High flow rate (80-90 L/min)

- Particles in most penetrating particle size

- Well-characterized inert particles (not biological, anthropogenic, or naturogenic)

Instruments that quantify collection efficiency in narrow size categories

N95 FFR or similar as positive controlInclude

Filter Efficiency of Face Covering Materials

Collection efficiency of 0.3 µm at 99 L/min

• Fleece towel (cotton & polyester/nylon) & polyester scarf materials - 20% collection efficiency (highest breathing resistance)

• Commercial cloth masks, sweatshirt & cotton scarf materials - 10%

• T-shirts – 1%

20% Collection Efficiency - Highest Breathing Resistance

10% Collection Efficiency

Rengasamy, S., Eimer, B., & Shaffer, R. E. (2010). Simple respiratory protection—evaluation of the filtration performance of cloth masks and common fabric materials against 20–1000 nm size particles. Annals of occupational hygiene, 54(7), 789-798.

Surgical Masks Filter

Performance Using NIOSH

Test Conditions

• Collection efficiency of surgical mask filters is highly variable, ranging from 2 to 98%

• Most surgical mask filter efficiencies range from 30-50%

• Impossible to predict the collection efficiency of a surgical mask

• Bacterial efficiency tests are not predictive of performance in most penetrating particle size range

Respirator Filter Performance

• NIOSH certification tests evaluate the performance of filters by measuring collection efficiency using NaCl (solid) and DOP (liquid oil) aerosols (0.3 µm) charge neutralized at 85 L/min

• 3 categories of oil resistance

• N = not resistant to oil, R = resistant to oil, P = oil proof)

• 3 levels of filter efficiency

• 95 = 95% efficient, 99 = 99%, 100 = 99.97%

• 9 possible classes of respirators (3 oil resistance x 3 efficiencies)

Airflow Resistance Testing

Use

Worst case test conditions

- High flow rate (80-90 L/min)

- Evaluate in both directions (inhalation & exhalation)

Standardized instruments and test method

• N95 FFR or similar as positive controlInclude

Air Flow Resistance[at 85 L/min]

• Cloth face coverings• No standards or testing• Single layer = low resistance• Multiple layers = increasing resistance• Most < 10 mm H2O

• Surgical masks• No standards or testing• Few studies – range 9-14 mm H2O

• Respirators• NIOSH requirements

• Inhalation ≤ 35 mm H2O• Exhalation ≤ 25 mm H2O

• Most filtering facepiece respirators < 15 mm H2O

Inward Leakage = Fit Testing

Use

- Panel of human subjects with range of face sizes representative of the wearer population

- Quantitative sampling method

- Exercises that reflect real-world activities

Standardized instruments and test method

• N95 FFR or similar as positive controlInclude

Inward Leakage Using Quantitative Fit Test Method

• Cloth face coverings• Inward leakage of 65-90% (Fit factor = 1.1-1.5)

• Surgical masks with good filters• Inward leakage of 10-25% (Fit factor = 4-10)

• Respirators• Filtering facepiece respirator must achieve a

fit factor of 100 in workplace (1% inward leakage)

• One study of naïve subjects on 1 FFR• 90% got fit factor of 5 (20% inward leakage)

• 80% got fit factor of 10 (10% inward leakage)

• 20% got fit factor of 50 (2% inward leakage)

Outward Leakage =Source Control

Use

- Panel of human subjects with range of face sizes representative of the wearer population

- Quantitative sampling method

- Exercises that reflect real-world activities

Standardized instruments and test method

• N95 FFR or similar as positive controlInclude

Challenges for Outward Leakage Testing

Environment outside of the facepiece needs to be entirely clean – no particles!

Outward leakage = outside concentration / inside concentration

“Test aerosol” = particles emitted by the person during breathing & talking

No standardized, validated methods for measuring outward leakage to date

Inward leakage (fit) is not equivalent to outward leakage if the filter efficiency is low.

Outward Leakage Test Apparatus

Lindsley, William G., Francoise M.

Blachere, Brandon F. Law, Donald H.

Beezhold, and John D. Noti. "Efficacy

of face masks, neck gaiters and face

shields for reducing the expulsion of

simulated cough-generated aerosols."

Aerosol Science and Technology

(2020): 1-12.

Inward & Outward Leakage

Lindsley, William G., et al. "A comparison of

performance metrics for cloth face masks as

source control devices for simulated cough

and exhalation aerosols." medRxiv (2021).

https://www.medrxiv.org/content/10.1101/20

21.02.16.21251850v1

FacepieceMannequin

Outward

Leakage

Human

Total

Inward

Leakage

Filter

Efficiency

Airflow

Resistance

(mm H2O)

Average of 2 N95 FF

Respirators 3% 2% 99% 11

3M 1818 SM 9% 10% 93% 5

Procedure Mask 58% 59% 80% 11

Average of 9 cloth

masks 45% 65% 31% 9

Average of 5 1-layer

gaiters 55% 91% 4% 2

Average of 5 2-layer

gaiters 49% 77% 5% 3

FACE COVERINGS

SURGICAL MASKS

RESPIRATORS

Overview

• Barrier face covering = a product worn on the face specifically covering at least the wearer’s nose and mouth with the primary purpose of providing source control and to provide a degree of particulate filtration to reduce the amount of inhaled particulate matter.

• Not a respirator or a medical/surgical mask

• PROBLEM:

• Lots of products in the marketplace

• No standard test methods

• Impossible for the consumer to make an informed decision about quality

Overview

• Use or adapt existing test methods for evaluating face covering performance

• Must be able to accommodate a wide range of potential products

• Performance standard

• Puts all face coverings on the same playing field, allowing comparison between them

• Provides manufacturers with a set of specifications, guidelines and expectations

• Allows for the development of criteria to meet the needs of different user populations

Filter Efficiency

• Adapted procedures from 42 CFR Part 84 and NIOSH STP 0059

• Special attention to specimen mounting

• Sub-Micron Particulate Filtration Efficiency

• 10 specimens

• If re-useable, 10 specimens after maximum cleaning cycles

• Test entire product (unless extends beyond an ordinary facepiece)

• Pre-condition at 85 ± 5% RH & 38 ± 2.5C for 25 ± 1 hr

• Test at face velocity of 10 ± 0.5 cm/sec and 85 ± 4 L/min

• Charge neutralized NaCl aerosol with CMD of 0.075 ±0.02 µm & GSD of 1.86

• Report as percent filtration efficiency

Air Flow ResistanceMeasure air flow resistance in mm H20

at 85 ± 2 L/min andface velocity of 10 cm/sec

Leakage Assessment

Product design analysis self-declaration

“Product minimizes leakage around the perimeter or other areas of the product based on analysis of the product design.”

For re-useable products must be applied to new condition and after maximum cleaning cycles.

Examples of product design analysis:

Dimensional analysis, computer modeling, observation and measurement of coverage on standardized head or head-torso…

Quantitative Leakage Testing -Optional

• Manufacturer may also conduct quantitative fit testing to supplement the design analysis.

• Must be evaluated using ASTM F3407-20: Standard Test Method for Respirator Fit Capability for Negative-Pressure Half-Facepiece Particulate Respirators, with some modifications.

• “One size fits all” product must include subjects in cells 4 & 7, then cells 1, 3, 5, 8 and 10 if more data are needed.

• Leakage ratio = average results of 10 subjects from any of these cells.

• Products with sizes must include 10 subjects in designated cells.

Quantitative Leakage Test

• If use a CNC:• 2000 particle/cm3

• N99 mode only

• Subjects receive instructions only through written or video information

• Face covering donning must be without assistance

Performance Classification

Barrier Face Coverings for Workers in Lowest Risk Categories

Proposal to OSHA