PPE CASE

Personal Protective Equipment Conformity Assessment Studies and Evaluations

Performance of Stockpiled Air-Purifying Respirators, Facility Nine

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 Nine of Ten. This facility is a regional stockpile facility. 

NIOSH found that 172 of 172

N95 filtering facepiece 

respirators stockpiled at Facility 

Nine that were 15 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 Nine

• NIOSH researchers visited Facility Nine in November 2018 (Figure 1). This facility was located within the 

U.S. Department of Health and Human Services Region 8, representing Colorado, Montana, North 

Dakota, South Dakota, Utah, and Wyoming. 

Assessment of Storage Conditions

• Respirators were stored in a trailer for at least seven years and were recently moved into a building 

basement (approximately in October 2018, one month prior to product sampling).

• 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 Nine such as location and type of 

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

• NIOSH collected facility temperature and percent relative humidity (%RH) data by placing one data 

logger in the trailer. This data was collected in 60-minute intervals from November 2018 to August 2019. 

Collection of Respirator Samples

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

Samples were collected from two different manufacturing models1

: 1) Kimberly Clark (KC) 46727 and 2)

KC 46827 (Table 1). 

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

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

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

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

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

.

• Control respirators were purchased from the open market to be used as a comparison between 

stockpiled and new respirators.

Table 1. FFRs Sampled from Stockpile Facility Nine

Model Lot # Year of 

Manufacture

Shelf Life on 

Packaging?

Respirator Age at 

Time of Testing3

Shelf Life 

Status at Time 

of Testing

KC 46727 Lot A 2003 No 15 years

Past 5-year shelf 

life4 KC 46727 Lot B 2003 No

KC 46827 Lot A 2003 No

15 years

Past 5-year shelf 

life4 KC 46827 Lot B 2003 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 KC 46827 and 46727 controls were manufactured in 2017. 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 2018.

4 KC designated a five-year shelf life for this model [KC 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 observed at Facility Nine. Many product 

cases and boxes were opened. Twelve product boxes showed damage due to crushing, mold, and/or

dust. Examples of damage observed on product boxes are shown in Figures 2A and B. Of the 172

respirators visually inspected, 43 concerns were noted. An example of damage observed to the 

respirator is shown in Figure 3.

Figure 3: Most amount of damage observed on (A) and in (B) product boxes from Facility Nine.

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.

A B
5

Figure 3: Most amount of damage observed to respirators from Facility Nine.

• Temperature and %RH were not controlled or monitored. Lights were off when not in use. No evidence 

of excess moisture or chemical spills that persisted beyond immediate mitigation were observed. Dust 

was limited. No air circulation existed. Trailer was always kept outside in direct sunlight. Products were 

not shrink-wrapped.

• Percent RH (Figure 4) and Temperature (Figure 5)

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

temperature are to remain under 60 %RH and to remain within 68°F to 77°F [KC 2020].

o The average temperature between the 2018-2019 time period was 52.3°F. The average %RH 

between 2018-2019 was 34.2%; this average temperature deviates from KC’s recommended 

temperature storage condition but is within the recommended %RH storage condition.

o 72.9% of temperature data points were below 68°F and 16.6% were above 77°F. For %RH, no 

data points deviated from KC’s recommended conditions.
6

Figure 4: Percent Relative Humidity (% RH) from November 2018 – August 2019 for one data logger stored at 

Facility Nine. Data is plotted as a 20-point moving average for visualization purposes. Maximum and minimum 

temperatures reported are noted for each data logger.

Figure 5: Temperatures from November 2018 – August 2019 for one data logger stored at Facility Nine. Data is 

plotted as a 20-point moving average for visualization purposes. Maximum and minimum temperatures 

reported are noted for each data logger.
7

Inhalation and Exhalation Resistance

• NIOSH evaluated the inhalation and exhalation resistance for a total of 12 stockpiled and 6 control 

respirators. All stockpiled and control respirators from each model passed these tests (Figure 6).

• 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 found 

with respect to inhalation and exhalation resistance: 1) both of the KC 46727 stockpiled 2003 Lots A and 

B were lower; 2) KC 46827 stockpiled 2003 Lot A was lower; and 3) KC 46827 stockpiled 2003 Lot B was 

higher. 

• For inhalation resistance, the individual stockpiled respirator with the highest resistance (17.27 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 (16.00 mm H2O) 

was below the NIOSH maximum limit for product approval (25 mm H2O allowable maximum).
8

Figure 6: 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.
9

Filtration Performance

• NIOSH evaluated the particulate penetration efficiency for 160 stockpiled respirators and 40 controls 

(Figure 7). 

• None of the individual stockpiled respirators tested exceeded the 5.0% maximum. The highest 

penetration for an individual stockpiled respirator was 2.92% and the highest penetration for an 

individual control respirator was 4.93%. 

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

α<0.05) between the FFR controls and the FFR stockpiled respirators 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) both of the KC 46727 stockpiled 2003 Lots A and B had a lower penetration; and 2) KC 

46827 stockpiled 2003 Lot B had a higher penetration. 

Figure 7: 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.
10

CASE Findings

Findings for the KC 46727 and 46827 Models:

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. These 

models currently have a five-year recommended shelf life; Appendix 1 shows a KC letter to end users with shelf 

life information, which states respirators past their shelf life should be discarded [KC 2018]. Thus, these 

respirators tested are past their recommended shelf life. These findings are based on units evaluated from 

Facility Nine and may not be applicable at other stockpile facilities and/or under different environmental storage 

conditions.

Stockpile Storage Conditions:

For the KC models, 89.5% of temperature data points deviated from the previously described recommended 

storage conditions. For %RH, no data points deviated from the previously described recommended conditions. 

Stored under these conditions, NIOSH found that 172 N95 FFRs evaluated in this study, which were 15 years old, 

maintained their inhalation and exhalation resistance and filtration performance (i.e. all sampled 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 

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.

7 An approval may be granted to a non-manufacturing entity.
11

How Can You Learn More About the Respirators in Your 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. 
12 

Suggested Citation 

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

Respirators: Facility Nine 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 P2020-0109. 

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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/.

Carias C, Rainisch G, Shankar M, Adhikari BB, Swerdlow DL, Bower WA, Piliai SK, Meltzer MI, Koonin LM [2015]. Potential 

demand for respirators and surgical masks during a hypothetical influenza pandemic in the United States. Clinical 

Infectious Diseases 60 (1): S42-S51 https://doi.org/10.1093/cid/civ141.

DHHS [2012]. An HHS retrospective on the 2009 H1N1 influenza pandemic to advance all hazards preparedness. 

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KC [2020]. Kimberly Clark representatives, email correspondence, February 25, 2020.

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https://www.cdc.gov/niosh/npptl/topics/respirators/pt84abs2.html.

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https://www.cdc.gov/niosh/topics/healthcare/default.html. 

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https://www.cdc.gov/niosh/npptl/stps/apresp.html.

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https://www.cdc.gov/niosh/npptl/resources/pressrel/letters/conformitynotice/CA-2019-1012.html.

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Appendix 1 [KC 2018]