PPE CASE

Personal Protective Equipment Conformity Assessment Studies and Evaluations

Performance of Stockpiled Air-Purifying Respirators, Facility Two 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

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 details the inhalation/exhalation resistance and filtration performance of N95 filtering facepiece 

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

NIOSH found that 301 of 301 

N95 filtering facepiece 

respirators stockpiled at Facility 

Two 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 Two

• NIOSH researchers visited Facility Two in November 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 researchers documented storage practices at Facility Two 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 Two

stockpile personnel. This data was collected in 30-minute intervals from September 2013 to August 

2016.

Collection of Respirator Samples

• NIOSH collected samples for three APR models stockpiled at Facility Two. Facility Two’s inventory 

included APRs that are classified as N95 filtering facepiece respirators (FFRs). Samples were collected

from two different manufacturing models1

: 1) 3M 1860 (three different manufacturing years) and 2) 

Gerson 1730 (one manufacturing year) (Table 1). 

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

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

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

performance within common respirator models when stored under disparate conditions.
3

were sampled to evaluate and attempt to account for inter-lot variation. Products were sampled 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)2.

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 Two.

Table 1. FFRs Sampled from Stockpile Facility Two

Model Lot # Year of 

Manufacture

Shelf Life on 

Packaging?

Respirator Age at 

Time of Testing3

Shelf Life 

Status at Time 

of Testing

3M 1860 Lot A 2006 No 11 years Past 5-year shelf 

life 4 3M 1860 Lot B 2006 No

3M 1860 Lot A 2008 No

9 years

Past 5-year shelf 

life4 3M 1860 Lot B 2008 No

3M 1860 Lot A 2009 No

8 years

Past 5-year shelf 

life4 3M 1860 Lot B 2009 No

Gerson 1730 Lot A 2006 No 11 years No shelf life 

Gerson 1730 Lot B 2006 No designated

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 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.

2 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].

3 Testing was completed in 2017. 4 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) 35 35

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

STP 59: Particulate Filter 

Efficiency for N95

<5.0% particulate penetration 

(>95.0% filter efficiency) 406 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 Two; 

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

Of the 301 respirators visually inspected, twelve concerns were noted which involved respirator nose 

foam sticking to adjacent units for the 3M 1860 model (Figure 4).

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

5 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. 6 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 Two. 

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

• Facility Two shared the warehouse space with another entity. On Facility Two’s side, facility lights were 

off when not in use and no windows allowed sunlight to enter the facility. Stockpile personnel noted 

that although temperature and %RH are monitored, there is no air-conditioning, but fans exist and 

circulate air throughout the facility. No evidence of excess moisture or chemical spills that persisted 

beyond immediate mitigation were observed. Generally, the pallets were shrink wrapped around the 

four pallet sides but not across the top or bottom. Pallets were separated by metal racks, preventing 

weight/load applied to individual pallets.

• 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]

o The average temperature between the 2013-2016 time period was 73.3°F. The average %RH 

between 2013-2016 was 40.4%; these averages are within the 3M and Gerson recommended 

temperature and %RH storage conditions.

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

3M 1860 or the Gerson 1730 respirator models.
6

o Some respirators from Facility Two 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 recommended conditions.
7

Figure 5: Percent Relative Humidity (% RH) from September 2013 – June 2016 for two data loggers stored at 

Facility Two. 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 September 2013 – June 2016 for two data loggers stored at Facility Two. 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 21 stockpiled and 6 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 Gerson 1730 stockpiled 2008 Lot A was statistically 

significantly higher for both inhalation and exhalation resistance. The mean inhalation and exhalation 

resistance values are shown in Figure 7. 

• For inhalation resistance, the individual stockpiled respirator with the highest resistance (10.40 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 (9.63 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 280 stockpiled respirators and 40 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 2006 Lot A had a higher penetration; 2) 3M 1860 stockpiled 2008 Lot A 

had a higher penetration; 3) 3M 1860 stockpiled 2008 Lot B had a lower penetration; 4) 3M 1860 

stockpiled 2009 Lot B had a lower penetration; and 5) Gerson 1730 stockpiled 2008 Lot A had a higher 

penetration. The mean percent particle penetration for each lot of respirators tested is shown in Figure 

8.

• None of the individual respirators tested exceeded the 5.0% maximum. The highest penetration for an 

individual stockpiled respirator was 2.82% and the highest penetration for an individual control 

respirator was 1.59%, both being below the NIOSH maximum limit for product approval. 

• Additionally, the respirator shown in Figure 4 is an example of one of 12 respirators where the nose 

foam stuck together. The highest maximum penetration when these units were tested was 1.61%, 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.
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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 Two 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 designated shelf life; the Appendix 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 Two 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 Two to the NIOSH research team suggests that both 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 301 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 holder7 (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 

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 

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

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

regarding the use of product beyond the manufacturer- designated shelf life.

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. 
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Suggested Citation 

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

Respirators: Facility Two of Ten. By Greenawald, L., Moore, S., and Yorio, P. 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 P2020-0102. 

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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. 

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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 

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15

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Appendix [3M 2020]
17
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