PPE CASE

Personal Protective Equipment Conformity Assessment Studies and Evaluations

Performance of Stockpiled Air-Purifying Respirators, Facility Six 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 Six of Ten. This facility is a state stockpile facility. 

NIOSH found that 387 of 387 N95 

filtering facepiece respirators 

stockpiled at Facility Six that were 

11-12 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 Six

• NIOSH researchers visited Facility Six in April 2018 (Figure 1). This facility was located within the U.S. 

Department of Health and Human Services Region 10, representing Alaska, Idaho, Oregon, and 

Washington. 

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 Six 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 Six

stockpile personnel. This data was collected intermittently from January 2013 to November 2017. The 

data included temperatures taken at five different locations, which were averaged.

Collection of Respirator Samples

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

Samples were collected from four different manufacturing models1

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

46827; 3) Moldex 2201; and 4) 3M 8000 (Table 1). 

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

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

sampled to evaluate and attempt to account for inter-lot variation. More than two lots were sampled 

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

from a model if conditions presented “worst-case scenario” conditions within the facility. 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 Six. 

Table 1. FFRs Sampled from Stockpile Facility Six

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 2006 No 12 years

Past 5-year shelf 

life 4 KC 46727 Lot A 2006 No

KC 46827 Lot A 2007 No

11 years

Past 5-year shelf 

life4 KC 46827 Lot B 2007 No

Moldex 2201 Lot A 2006 Yes - 2010 12 years

Past 9-year shelf 

life Moldex 5 2201 Lot B 2006 Yes - 2010

3M 8000 Lot A 2006 No

12 years Past 3-year shelf 

life6 3M 8000 Lot B 2006 No

3M 8000 Lot C 2006 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, the Moldex 2201 controls 

were manufactured in 2018, and the 3M 8000 controls were manufactured in 20067

. 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).

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 5 Moldex designated a nine-year shelf life for these models [Moldex 2015]. In 2006, the shelf life was designated as four 

years, but was changed in 2009 to nine years. As of February 2020, these models still have a nine-year shelf life. 6 3M designated a three-year shelf life for this model. This model is no longer produced or sold by 3M. 7 3M 8000 is no longer manufactured thus NIOSH was not able to purchase new units to be used as controls.
4

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

performance of sampled respirators and control respirators.

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) 38 38

STP 7: Inhalation Resistance <35 mm H2O column @ 85 LPM 38 38

STP 59: Particulate Filter 

Efficiency for N95

<5.0% particulate penetration 

(>95.0% filter efficiency) 409 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 Six; 

examples of the most amount of dust is shown in Figure 2. No product boxes showed damage. Of the 

387 respirators visually inspected, no concerns were noted.

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

• Temperature and %RH were controlled and intermittently monitored. Back-up generator existed in case 

of power outage. Facility lights were off when not in use. Ceiling fans continuously ran to circulate air. 

8 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. 9 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

No evidence of excess moisture or chemical spills that persisted beyond immediate mitigation were 

observed. Pallets were generally shrink wrapped around the four pallet sides and across the top. 

Generally, all pallets were separated by rack, reducing weight/load applied to a single pallet. 

• Percent RH (Figure 3) and Temperature (Figure 4)

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

are

 KC 46727 and 46827: remain under 60 %RH; remain within 68°F to 77°F [KC 2020]

 Moldex 2201: no specific %RH recommendations; remain within 14°F and 122°F [Moldex 

2019]

 3M 80007

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

o Temperature data was averaged across the five temperature collection locations. The average 

temperature between the 2013-2017 time period was 71.4°F. The average %RH between 2013-

2017 was 34.0%; these averages are within KC, Moldex, and 3M’s recommended temperature 

and %RH storage conditions.

o For the KC models, 2.6% of data points were below 68°F and 0.3% were above 77°F. No 

temperature data points deviated from Moldex or 3M’s recommended conditions. For %RH, no 

data points deviated from KC, 3M, or Moldex’s recommended storage conditions.

o Some respirators from Facility Six 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.
6

Figure 3: Percent Relative Humidity (% RH) from January 2013 – November 2017 taken at one location within 

Facility Six. Data is plotted as a 5-point moving average for visualization purposes. Maximum and minimum 

temperatures reported are noted for each data logger.
7

Figure 4: Temperatures from January 2013 – November 2017 taken at five locations within Facility Six. Data is 

plotted as a 5-point moving average for visualization purposes. Maximum and minimum temperatures reported 

are noted for each data logger.
8

Inhalation and Exhalation Resistance

• NIOSH evaluated the inhalation and exhalation resistance for a total of 27 stockpiled and 12 control 

respirators. All stockpiled and control respirators from each model passed these tests (Figure 5).

• 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 exhalation resistance: 1) 3M 8000 stockpiled 2006 Lots A and B were statistically 

significantly higher; 2) KC 46827 stockpiled 2007 Lot A was significantly lower; and 3) Moldex 2201 

stockpiled 2006 Lot A was significantly higher. The following statistically significant differences were 

found with respect to inhalation resistance: 1) 3M 8000 stockpiled 2006 Lots A and B were statistically 

significantly higher; 2) KC 46827 stockpiled 2007 Lots A and B were significantly lower; and 3) Moldex 

2201 stockpiled 2006 Lot A was statistically significantly higher. 

• For inhalation resistance, the individual stockpiled respirator with the highest resistance (15.75 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 (14.22 mm H2O) 

was below the NIOSH maximum limit for product approval (25 mm H2O allowable maximum).
9

Figure 5: 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.
10

Filtration Performance

• NIOSH evaluated the particulate penetration efficiency for 360 stockpiled respirators and 80 controls. 

• None of the individual stockpiled respirators tested exceeded the 5.0% maximum (Figure 6). The highest 

penetration for an individual stockpiled respirator was 4.82% (KC 46727) and the highest penetration for 

an individual control respirator was 4.93% (KC 46727). 

• Using an analysis of variance (ANOVA), there was not a statistically significant difference (defined as 

α<0.05) between KC control and KC stockpiled respirators. 3M controls (mean percent 

penetration=2.45%, SD=0.36) displayed a significantly higher penetration when compared to 3M 

stockpiled respirators (mean percent penetration=1.75%, SD=0.67) when averaging across models; and 

Moldex controls (mean percent penetration=1.66%, SD=0.31) displayed a statistically significantly higher 

penetration when compared to Moldex stockpiled respirators (mean percent penetration=0.74%, 

SD=0.31) 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) each of the 3M 8000 stockpiled 2006 Lots had a lower penetration; 2) KC 46727 stockpiled 

2006 Lot A had a lower penetration; 3) KC 46827 stockpiled 2007 Lot A had a higher penetration; and 4) 

both Moldex 2201 stockpiled 2006 Lots A and B had a lower penetration.

Figure 6: 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.
11

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. This model 

currently has 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 pertain to KC units from Facility Six and may not be 

applicable to other stockpile facilities and/or under different environmental storage conditions.

Findings for the 3M 8000 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

is no longer produced and sold by 3M. Additionally, Appendix 2 shows two 3M letters to end users with shelf 

life and recommended storage condition information [3M 2018, 3M 2020]. Thus, all respirators tested are past 

their recommended shelf life. These findings pertain to 3M units from Facility Six and may not be applicable to

other stockpile facilities and/or under different environmental storage conditions.

Findings for the Moldex 2201 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 nine-year recommended shelf life; Appendix 3 shows a Moldex memo to customers and 

distributors with shelf life and recommended storage condition information [Moldex 2015]. Thus, all respirators 

tested are past their recommended shelf life. These findings pertain to Moldex units from Facility Six and may 

not be applicable to other stockpile facilities and/or under different environmental storage conditions.

Stockpile Storage Conditions:

For the KC models, 2.9% of data points deviated from the previously described recommended conditions. No 

temperature data points deviated from Moldex or 3M’s recommended conditions. For %RH, no data points 

deviated from KC, 3M, or Moldex’s recommended storage conditions. Stored under these conditions, NIOSH 

found that 387 N95 FFRs evaluated in this study, which were 11-12 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 holder10 (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. 

10 An approval may be granted to a non-manufacturing entity.
12

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.

NIOSH recommends users contact 3M regarding use of 3M model 8000 respirators.
13

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. 
14 

Suggested Citation 

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

Respirators: Facility Six 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 P2020-0106. 

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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 

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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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15

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16

Appendix 1 [KC 2018]
17

Appendix 2 [3M 2018], [3M 2020]
18
19
20
21
22

Appendix 3 [Moldex 2015]