PPE CASE

Personal Protective Equipment Conformity Assessment Studies and Evaluations

Performance of Stockpiled Air-Purifying Respirators, Facility One of 

Ten: Inhalation and Exhalation Resistance and Filtration Efficiency 

Performance

National Institute for Occupational Safety and Health (NIOSH)

National Personal Protective Technology Laboratory (NPPTL)

Lee A. Greenawald, Susan M. Moore, Patrick L. Yorio, Kerri Wizner

March 1, 2020

In the event of a national emergency, eighteen million U.S. healthcare 

workers may face high-consequence infectious disease exposures

[NIOSH 2017]. Personal protective equipment (PPE), such as gowns, 

gloves, goggles, and respirators, is an important measure within the

infection prevention hierarchy of controls. During public health 

emergencies, the sudden increase in PPE demand may exceed 

supplies for upwards of three months while manufacturers increase 

production [ASTHO 2013; Carias et al. 2015]; [Patel et al. 2017]. For 

example, during the 2009 H1N1 pandemic, local respirator shortages were reported and, during the 2016 Ebola 

outbreak and the first U.S. fatality, there was a 10-200 fold increase in PPE orders [DHHS 2012; NIOSH 2018]. To 

prepare for these shortages, large quantities of PPE are strategically stockpiled at hospital, local, state, and 

federal facilities [NIOSH 1997].

Due to the decision to stockpile PPE, stockpile personnel and decision makers have sought to understand if 

stockpiled PPE is still viable following long-term storage. NIOSH does not require approval holders (i.e. those 

granted the approval from NIOSH) to designate a shelf life for particulate-only air-purifying respirators (APR), 

although some choose to do so and may provide this information on product packaging or online. There is 

limited published data to understand the viability of respirators that have undergone long-term storage with or 

without a designated shelf life. Over the past decade, the Strategic National Stockpile (SNS) and state and local 

stockpile personnel asked NIOSH to evaluate the performance of stockpiled PPE as well as better understand 

storage conditions in U.S. stockpile facilities that store PPE. 

In 2017, NIOSH established a PPE Stockpile Partnership consisting of 1) federal entities and stockpiles; 2) state, 

county, and city stockpiles; 3) hospital-related stockpile entities; and 4) a manufacturer trade association to 

inform the design and execution of an empirical study to evaluate stockpiled APRs. NIOSH obtained samples of 

PPE from geographically dispersed stockpiles with varying storage conditions.

This report describes the inhalation/exhalation resistance and filtration performance of N95 filtering facepiece 

APRs collected from Facility One of Ten. This facility is a state stockpile facility.

NIOSH found that 344 of 344 N95 

filtering facepiece respirators 

stockpiled at Facility One that 

were 8-11 years old maintained 

their inhalation and exhalation 

resistance and filtration 

performance in accordance with 

NIOSH performance standards. 
2

How NIOSH Evaluated Respirators and Storage Conditions

Description of Facility One

• NIOSH researchers visited Facility One in August 2017 (Figure 1). This facility was located within the U.S. 

Department of Health and Human Services Region 2, representing New York, New Jersey, Puerto Rico, 

and the Virgin Islands. 

Assessment of Storage Conditions

• NIOSH, in conjunction with the PPE Partnership members, developed checklists to document site and 

packaging (i.e. pallet, case, and box) conditions that may impact respirator performance.

• NIOSH documented the following storage conditions: 1) the PPE packaging presence of dust, shrinkwrapping, chemicals, and moisture, 2) exposure to sunlight and direct light; 3) proximity to fans, 

windows, doors, and ventilation systems; 4) damage to pallet and product packaging; and 5) location of 

pallet on storage rack (e.g., top, bottom) and location of PPE product on pallet (e.g., top/not loadbearing, bottom/load-bearing).

Figure 1: NIOSH documented storage practices at Facility One such as location and type of lighting, 

pallet stacking practices, and conditions of the flooring, roofing, and exterior walls.

• NIOSH reviewed facility temperature and percent relative humidity (%RH) data provided by Facility One

stockpile personnel. This data was collected in 30-minute intervals from March 2014 to February 2017.

Collection of Respirator Samples

• Facility One’s inventory included APRs that are classified as N95 filtering facepiece respirators (FFRs). 

Samples were collected from three different manufacturing models1

: 1) 3M 1860 (two different 

manufacturing years); 2) Gerson 1730; and 3) Medline/Alpha ProTech (APT) NON275012 (Table 1). 

• Upon reviewing the detailed APR inventories and storage location by lot within Facility One, two 

different manufacturing lots for each model were identified and sampled within Facility One. Two lots 

1 Based on the other nine collaborating stockpiles’ inventories, these three models were sampled in order to compare 

performance within common respirator models when stored under disparate conditions.

2 The FFR model NON27501 has been manufactured by Alpha ProTech as a private label to Medline under TC-84A-0457.
3

were sampled to evaluate and attempt to account for inter-lot variation. Products were collected and 

shipped to the NIOSH facility overnight to reduce exposure to non-climate-controlled conditions. 

• Forty-three respirators were tested from each manufacturing lot for inhalation and exhalation

resistance (n=3) and filtration performance testing (n=40)3.

Selection of Control Respirators

• Control respirators of the same model as those sampled from the facility were purchased from the open 

market to be used as a comparison between stockpiled and new respirators.

Characteristics of Sampled Respirators

• Table 1 provides a summary of the respirator models sampled from Facility One. 

Table 1. FFRs Sampled from Stockpile Facility One

Model Lot # Year of 

Manufacture

Shelf Life on 

Packaging?

Respirator Age at 

Time of Testing4

Shelf Life 

Status at Time 

of Testing

3M 1860 Lot A 2009 No 8 years Past 5-year shelf 

life 5 3M 1860 Lot B 2009 No

3M 1860 Lot A 2008 No

9 years

Past 5-year shelf 

life3 3M 1860 Lot B 2008 No

Gerson 1730 Lot A 2006 No 11 years No shelf life 

Gerson 1730 Lot B 2006 No designated

Medline/APT 

NON 27501 Lot A 2008 No

9 years No shelf life 

Medline/APT designated

NON27501 Lot B 2008 No

Evaluation of Inhalation and Exhalation Resistance and Filtration Performance

• Twenty-three control respirators were tested for inhalation and exhalation resistance and filtration 

performance. The Gerson 1730 and Medline/APT NON27501 controls were manufactured in 2017 

and the 3M 1860 controls were manufactured in 2018. NIOSH testing requirements state that a 

minimum of three respirator units must be tested for inhalation and exhalation resistance. The same 

three respirators can be used for both inhalation and exhalation resistance testing [NIOSH 2018].

• Inhalation and exhalation resistance and filtration performance of the stockpiled and control 

respirators were evaluated using the same Standard Test Procedures (STPs) NIOSH uses for 

approving respirators under 42 Code of Federal Regulations Part 84, “Approval of Respiratory 

Protective Devices” [NIOSH 2018] (Table 2). 

• Table 2 describes the method for evaluating the inhalation and exhalation resistance and filtration 

performance of sampled respirators and control respirators.

3 NIOSH testing requirements state that a minimum of three respirator units must be tested for inhalation and exhalation 

resistance and a minimum of 20 must be tested for filtration efficiency [NIOSH 2018]. 4 Testing was completed in 2017.

5 In 2013, 3M designated a five-year shelf life for the 3M 1860 model [3M 2018]. As of February 2020, this model still has a 

five-year shelf life.
4

Table 2. NIOSH Tests Conducted to Evaluate Inhalation and Exhalation Resistance and Filtration 

Performance. 

NIOSH Standard Test 

Procedures (STPs)

Pass/Fail Criteria for APRs Stockpiled Respirators 

Tested Per 

Manufacturing Lot

Control Respirators 

Tested

STP 3: Exhalation Resistance <25 mm H2O column @ 85 liters 

per minute (LPM) 36 36

STP 7: Inhalation Resistance <35 mm H2O column @ 85 LPM 36 36

STP 59: Particulate Filter 

Efficiency for N95

<5.0% particulate penetration 

(>95.0% filter efficiency) 407 20

What NIOSH Found Through Inspection, Testing, and Evaluation 

Storage Conditions

• Visual Inspections—Dust and damage to product packaging was limited or not observed at Facility One; 

examples of the most amount of dust and damage to product packaging are shown in Figures 2 and 3. 

Of the 344 respirators visually inspected, only one concern was noted, which was a slight deformation to 

one Gerson 1730 respirator (Figure 4).

Figure 2: Most amount of dust observed on product cases from Facility One.

6 NIOSH testing requirements state that a minimum of three respirator units must be tested for inhalation and exhalation 

resistance. The same three respirators can be used for both inhalation and exhalation resistance testing.

7 An increased sample size was used for the stockpiled respirators as opposed to the control respirators to increase the 

precision of the performance estimates investigated.
5

Figure 3: Most amount of product case damage observed from Facility One. 

Figure 4: Most amount of product damage observed from Facility One.

• Temperature was controlled; temperature and %RH were monitored. Facility lights were off when not in 

use and no windows allowed sunlight to enter the facility. No evidence of excess moisture or chemical 

spills that persisted beyond immediate mitigation were observed. Pallets were shrink wrapped around 

the four pallet sides but not across the top or bottom. With the exception of the top-most row, pallets 

were separated by racks. On the top-most row, pallets were stacked two-high causing some weight/load 

to be applied to the bottom pallet. 

• Percent RH (Figure 5) and Temperature (Figure 6)

o At the time of publication, the recommended storage requirements for %RH and temperature 

are

 3M 1860: remain under 80 %RH; remain within -4°F to 86°F [3M 2017]

 Gerson 1730: remain under 80 %RH; remain within -4°F to 95°F [Gerson 2019]

 Medline/APT NON27501: avoid excessive moisture (water droplets or direct submersion 

in water); avoid prolonged extreme temperatures (< 60°F and >80°F) [Alpha ProTech 

2019]

o The average temperature between the 2014-2017 time period was 71.3°F. The average %RH 

between 2014-2019 was 38.3%; these averages are within the 3M, Gerson, and APT 

recommended temperature and %RH storage conditions.

o No %RH or temperature data points deviated from the recommended storage conditions for the 

3M 1860, Medline/APT, or the Gerson 1730 respirator models.
6

o Some respirators from Facility One were previously stored and deployed from a federal SNS 

facility. Although the current tracking process does not allow for retrieval of the historical 

location(s) and environmental conditions for these sampled products, subsequent discussions 

with SNS leadership suggest that SNS storage conditions met the recommended conditions.
7

Figure 5: Percent Relative Humidity (% RH) from March 2014 – February 2017 for two data loggers stored at 

Facility One. Data is plotted as a 50-point moving average for visualization purposes. Maximum and minimum 

temperatures reported are noted for each data logger.
8

Figure 6: Temperatures from March 2014 – February 2017 for two data loggers stored at Facility One. Data is 

plotted as a 50-point moving average for visualization purposes. Maximum and minimum temperatures 

reported are noted for each data logger.
9

Inhalation and Exhalation Resistance

• NIOSH evaluated the inhalation and exhalation resistance for a total of 24 stockpiled and 9 control 

respirators. All stockpiled and control respirators from each model passed these tests (Figure 7).

• Using an analysis of variance (ANOVA), there were no statistically significant differences (defined as 

α<0.05) between the FFR controls and FFR stockpiled respirators for inhalation and exhalation 

resistance when averaging across models.

• When comparing the individual respirator models to their respective controls through an ANOVA with 

adjusted, post-hoc multiple comparisons, the following statistically significant differences were 

detected: 1) Gerson 1730 stockpiled Lot A had a statistically higher inhalation resistance; 2) Gerson 1730 

stockpiled Lot A had a statistically higher exhalation resistance; and 3) Medline/APT NON27501 

stockpiled Lot B had a statistically lower exhalation resistance. The mean inhalation and exhalation 

resistances values are shown in Figure 7.

• For inhalation resistance, the individual stockpiled respirator with the highest resistance (11.93 mm 

H2O) was below the NIOSH maximum limit for product approval (35 mm H2O allowable maximum). For 

exhalation resistance, the individual stockpiled respirator with the highest resistance (11.43 mm H2O) 

was below the NIOSH maximum limit for product approval (25 mm H2O allowable maximum).
10

Figure 7: Control and stockpiled respirator inhalation (A) and exhalation (B) resistance data. N95 FFRs must have 

an inhalation resistance less than 35 mmH2O and an exhalation resistance less than 25 mmH2O. The pass/fail 

threshold for inhalation (A) and exhalation (B) resistance is shown by the red line. Error bars represent the 99% 

confidence interval and estimate the population parameters. This confidence interval suggests that 99% of any 

repeated samples tested and evaluated from this lot will have a mean between the upper and lower bounds.
11

Filtration Performance

• NIOSH evaluated the particulate penetration efficiency for 320 stockpiled respirators and 60 controls. All 

stockpiled and control respirators from each model passed this test (Figure 8). 

• Using an analysis of variance (ANOVA), there were no statistically significant differences (defined as 

α<0.05) between the FFR controls and FFR stockpiled respirators for filtration when averaging across 

models.

• When comparing the individual respirator models to their respective controls through an ANOVA with 

adjusted, post-hoc multiple comparisons, the following statistically significant differences were 

detected: 1) 3M 1860 stockpiled 2008 Lot A had a higher penetration; 2) 3M 1860 stockpiled 2009 Lot B 

had a higher penetration; 3) Gerson 1730 stockpiled Lot B had a higher penetration; and 4) Medline/APT 

NON27501 stockpiled Lot A and B had a statistically significantly lower penetration. The mean percent 

particle penetration for each lot of respirators tested is shown in Figure 8.

• The individual stockpiled respirator with the highest penetration (4.43%) was nearly identical to the 

control respirator with the highest penetration (4.44%), with both being below the NIOSH maximum 

limit for product approval (5.0% penetration allowable). 

• Additionally, the respirator shown in Figure 4 that had a visual inspection concern had a value of 1.00% 

maximum penetration when tested and, therefore, was not the stockpiled respirator associated with the 

highest penetration.

Figure 8: Control and stockpiled respirator particle filtration performance data. N95 FFRs must have a particle 

penetration of less than 5.0%. Error bars represent the 99% confidence interval and estimate the population 

parameters. This confidence interval suggests that 99% of any repeated samples tested and evaluated from this 

lot will have a mean between the upper and lower bounds.
12

CASE Findings

Findings for the Gerson 1730 Model:

No failures for inhalation resistance, exhalation resistance, or filtration performance were observed—i.e., the 

performance data suggests that these units would be protective so long as a proper fit is achieved. No shelf 

life was designated for this model by the approval holder. These findings pertain to Gerson 1730 units from 

Facility One and may not be applicable to other stockpile facilities and/or under different environmental storage 

conditions.

Findings for the 3M 1860 Model: 

No failures for inhalation resistance, exhalation resistance, or filtration performance were observed—i.e., the 

performance data suggests that these units would be protective so long as a proper fit is achieved. This model 

currently has a five-year shelf life; Appendix 1 shows a 3M letter to end users with shelf life and recommended 

storage condition information [3M 2020]. Thus, these respirators tested are past their designated shelf life. 

These findings pertain to 3M units from Facility One and may not be applicable to other stockpile facilities 

and/or under different environmental storage conditions.

Findings for the Medline/Alpha ProTech NON27501 Model: 

No failures for inhalation resistance, exhalation resistance, or filtration performance were observed—i.e., the 

performance data suggests that these units would be protective so long as a proper fit is achieved. No shelf 

life was designated for this model (Appendix 2, [Alpha ProTech, 2020]). These findings pertain to Medline/Alpha 

ProTech units from Facility One and may not be applicable to other stockpile facilities and/or under different 

environmental storage conditions.

Stockpile Storage Conditions:

The data made available by Facility One to the NIOSH research team suggests that all three respirator models 

evaluated in this study were stored in an environment that was within the previously described 

recommendations for %RH and temperature. Stored under these conditions, NIOSH found that the 344 N95 

FFRs evaluated in this study, which were 8-11 years old, maintained their inhalation and exhalation resistance 

and filtration performance (i.e., all respirators were below the NIOSH maximum limit as defined by 42 CFR Part 

84). 

NIOSH regulation sets the minimum quality and performance requirements for the approval of respirators

[NIOSH 1997]. NIOSH does not have requirements for shelf life or storage conditions for particulate-only APRs. 

The approval holder8 (i.e. the entity that is granted the approval from NIOSH) is responsible for understanding 

how their products’ design or performance may be affected by various use or storage conditions and must 

provide instruction for establishing the proper use, storage, and maintenance procedures for their approved 

products, which may include designating a shelf life [NIOSH 2019]. FFR or particulate filter packaging (such as 

the box) often includes NIOSH-approved user instructions, label information, and recommendations on shelf life. 

Additionally, some approval holders also disseminate recommendations related to storage and shelf life through 

8 An approval may be granted to a non-manufacturing entity.
13

resources such as user and web notices. The respirators tested in this study were generally not designed for 

long-term storage.

At this time, we do not have enough information to definitively know the level of protection that may be 

provided by respirators that 1) are stored for prolonged periods of times; 2) are stored under various storage 

conditions; or 3) have exceeded the approval holder’s designated shelf life. Users of respirators that have 

exceeded the designated shelf life should be forewarned to avoid a false sense of confidence; these devices may 

not provide the same level of protection as those that have not exceeded the designated shelf life. We 

recommend contacting the approval holder(s) of the respirators in the stockpile with specific questions 

regarding the use of product beyond the designated shelf life.
14

What Can Stockpile Personnel Do to Learn More about the 

Respirators in their Stockpile?

• Stockpile personnel should check the product information from the approval holder as well as the 

NIOSH Certified Equipment List to remain up-to-date on product storage conditions, shelf-life 

information, and NIOSH approval status. Check NIOSH’s Certified Equipment List to verify the respirator 

model currently maintains its NIOSH approval at 

https://www.cdc.gov/niosh/npptl/topics/respirators/cel/default.html

• Stockpile personnel should work with the approval holder(s) of the stockpiled products with specific 

questions regarding the use of expired product. 

• Sign up for NPPTL’s Listserv at https://www.cdc.gov/niosh/npptl/sub-NPPTL.html to receive email 

notifications relevant to PPE.

For more information related to personal protective equipment, visit the NIOSH NPPTL website

https://www.cdc.gov/niosh/npptl/

Get More Information

Find NIOSH products and get answers to workplace safety and health questions:

1-800-CDC-INFO (1-800-232-4636) | TTY: 1-888-232-6348

CDC/NIOSH INFO: cdc.gov/info | cdc.gov/niosh

Monthly NIOSH eNews: cdc.gov/niosh/eNews

All photos courtesy of NIOSH NPPTL.

Disclaimer 

The recommendations in this report are made based on the findings at the stockpile evaluated and may not be 

applicable to other stockpile facilities. 

Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health 

(NIOSH). In addition, citations to websites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or 

their programs or products. Furthermore, NIOSH is not responsible for the content of these websites. All web addresses referenced in 

this document were accessible as of the publication date. 
15

Suggested Citation 

NIOSH [2020]. PPE CASE: Inhalation and Exhalation Resistance and Filtration Performance of Stockpiled Air-Purifying 

Respirators: Facility One of Ten. By Greenawald, L., Moore, S., Yorio, P., and Wizner, K. Pittsburgh, PA U.S. Department of 

Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and 

Health, NPPTL Report Number P2020-0101.

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3M [2018]. 3M Personal Safety Division Letter. St. Paul, MN: The 3M Company. 

https://multimedia.3m.com/mws/media/1430383O/3m-filtering-facepiece-shelf-life-letter.pdf. 

3M [2020]. Frequently Asked Questions: 3M Health Care Particulate Respirator and Surgical Masks Storage Conditions and 

Shelf Life. St. Paul, MN. http://multimedia.3m.com/mws/media/869238O/3m-health-care-particulate-respirator-andsurgical-masks-storage-conditions-and-shelf-life-faq.pdf 

Alpha ProTech [2019] Alpha ProTech Customer Service Representative, email correspondence, October 1, 2019. 

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Arlington, VA: Association of State and Territorial Health Officials. http://www.astho.org/Programs/Preparedness/PublicHealth-Emergency-Law/Emergency-Authority-and-Immunity-Toolkit/Federal-Emergency-Preparedness-Directives-andSystems-Fact-Sheet/.

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16

Patel A, D'Alessandro M, Ireland KJ, Burel WG, Wencil EB, Rasmussen SA [2017]. Personal protective equipment supply 

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Appendix 1 [3M 2020]
18
19
20

Appendix 2 [Alpha ProTech 2020]