1

PPE CASE

Personal Protective Equipment Conformity Assessment Studies and Evaluations

Inhalation and Exhalation Resistance and Filtration Performance of 

Stockpiled Air-Purifying Respirators: Overall Performance of Nearly 

4,000 Respirators Sampled from Ten Stockpile Facilities

National Institute for Occupational Safety and Health (NIOSH)

National Personal Protective Technology Laboratory (NPPTL)

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

March 25, 2020

This report details the results for inhalation and exhalation 

resistance and filtration performance from 3,971 APRs collected from 

ten U.S. stockpile facilities, including one federal stockpile, six state 

stockpiles, two regional stockpiles, and one county stockpile. Facilityspecific reports can be found on NIOSH’s PPE CASE Report website.

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 surge demands, 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 sampled and tested 

nearly 4,000 respirators from ten geographically dispersed stockpiles with varying storage conditions.

NIOSH found that 98% of the airpurifying respirators tested from 

ten stockpile facilities and 

manufactured between 2003-2013 

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 the Ten Facilities

• From 2017 to 2019, NIOSH researchers visited ten stockpile facilities, geographically dispersed across 

the U.S. These facilities included one federal stockpile, six state stockpiles, two regional stockpiles, and 

one county stockpile. These ten facilities represented the Department of Health and Human Services (HHS)

Regions 1, 2, 4, 6, 8, 9, and 10 as shown in Figure 1.

Figure 1. Figure shows locations of the ten collaborating stockpile facilities by the Department of Health 

and Human Services (HHS) national regions.

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. An example of 

a pallet, case, and box is shown in Figure 2.

• NIOSH documented site storage conditions, including the presence of: 1) dust, moisture, fans, windows, 

doors, and ventilations systems and 2) chemicals such as cleaning products, vermin traps, and pesticide 

treatment schedules—no indication of PPE product exposure was identified.

• NIOSH documented PPE pallet-specific storage conditions including: 1) the presence of dust, shrinkwrapping around the pallet, and moisture on the exterior packaging; 2) exposure to sunlight and direct 

light; 3) proximity to fans, windows, doors, and ventilation systems; 4) damage to shrink wrapping; and 

5) location of pallet on storage rack (e.g., top, bottom).

• NIOSH documented PPE case-specific storage conditions including: 1) the presence of dust and 

moisture; 2) exposure to sunlight and direct light; 3) proximity to fans, windows, doors, and ventilation 
3

systems; 4) damage to the case; and 5) location of case within the pallet (e.g., top/not load-bearing, 

bottom/load-bearing).

• For stockpiles where temperature and percent relative humidity (%RH) were monitored, NIOSH 

reviewed this data that was provided by the facility stockpile managers. Where these conditions were 

not monitored and therefore data was not available, NIOSH collected temperature and %RH data by 

placing data loggers in the facility, collecting temperature and %RH data for at least eight months, and in 

some facilities, up to one year (specifics provided in a later section).

Figure 2: Figure depicts the differences between the pallet, case, and box observed at one of the ten 

facilities
4

Collection of Respirator Samples

• Twelve different particulate APR models, manufactured between 2003 and 2013, were sampled from 

the ten facilities. These models were selected to ensure that commonly stockpiled models were 

included in the study. Of these twelve APR models, ten had shelf lives designated by the approval holder

at the time of this report—of these ten, all sampled models exceeded their shelf lives. Eleven of these 

models were N95 filtering facepiece respirators (FFR), and one model was a P95 particulate filter to be 

used with an elastomeric half mask. Where possible, at least two production lots within a manufacturing 

year were sampled for each respirator model within a facility. Two lots were sampled to evaluate and 

attempt to account for possible inter-lot variation. More than two lots were sampled if there were 

unique circumstances of interest to explore (e.g., packaging showed visible damage or was in indirect or 

direct sunlight). One lot was sampled if there was only one available for sampling.

• Upon NIOSH researchers visiting each facility, products were sampled and shipped to the NIOSH facility 

overnight to reduce exposure to non-climate-controlled conditions during transport. The samples were 

tested at the NIOSH facility in accordance with NIOSH performance requirements. 

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

resistance (n=3) and filtration performance testing (n=40)1

.

Characteristics of Sampled Respirators

• Table 1 provides a summary of the respirator models and quantity sampled from the ten facilities to test 

the inhalation and exhalation resistance and the filtration performance. The table also includes relevant 

storage condition and shelf life status information.

• NIOSH does not require approval holders to designate a shelf life, although some choose to do so. 

Additionally, many approval holders designated a shelf life after the models sampled from these 

stockpiles were manufactured.

1 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].
5

Table 1. Characteristics of the APRs Sampled from the Ten Collaborating Stockpile Facilities

Model

(Range of 

Manufacturing 

Year[s] Range of 

the Sampled Lots)

NIOSH TC 

Approval 

Number

# of Lots 

Sampled

Total # of 

Respirators 

Tested

Total # of the 

Ten 

Collaborating 

Facilities 

Stockpiling this 

Model

Shelf Life Status 

at Time of 

Testing2

Recommended Storage 

Conditions3

3M 1860 

(mfr. 2006 – 2011) 84A-0006 29 1,2194 8 Past 5-year shelf life

Remain under 80 %RH; 

remain within -4°F to 86°F

3M 1870 

(mfr. 2010 – 2013) 84A-3844 5 215 3 Past 5-year shelf life

Remain under 80 %RH; 

remain within -4°F to 86°F

3M 80005

(mfr. 2006 – 2008) 84A-3981 9 387 4 Past 3-year shelf life

Remain under 80 %RH; 

remain within -4°F to 86°F

3M 8210 

(mfr. 2006 and 

unknown6)

84A-0007 6 258 3 Past 5-year shelf 

life

Remain under 80 %RH; 

remain within -4°F to 86°F

3M 9010 

(mfr. 2006 – 2007) 84A-4243 6 258 3 Past 5-year shelf life

Remain under 80 %RH; 

remain within -4°F to 86°F

3M 2071 

(mfr. 2006) 84A-1647 4 172 2 Past 5-year shelf life

Remain under 80 %RH; 

remain within -4°F to 86°F

Gerson 1730 

(mfr. 2006) 84A-0160 5 215 3 No designated shelf life

Remain under 80 %RH; 

remain within -4°F to 95°F

Kimberly Clark 

46727 

(mfr. 2003 – 2007)

84A-0010 9 387 5 Past 5-year shelf 

life

Remain under 60 %RH; 

remain within 68°F to 77°F

Kimberly Clark 

46827 

(mfr. 2003 – 2007)

84A-0005 14 602 7 Past 5-year shelf 

life

Remain under 60 %RH; 

remain within 68°F to 77°F

Medline/Alpha 

ProTech 

NON27501 

(mfr. 2008)

84A-0457 2 86 1 No designated 

shelf life

Avoid excessive moisture 

(water droplets or direct 

submersion in water)7; avoid 

prolonged extreme 

temperatures (< 60°F and 

>80°F)

Moldex 1512 

(mfr. 2009) 84A-0013 2 86 1 Past 9-year shelf life

No specific %RH 

recommendations; remain 

with 14°F and 122°F

Moldex 2201N95

(mfr. 2006) 84A-2456 2 86 1 Past 9-year shelf 

life

No specific %RH 

recommendations; remain 

with 14°F and 122°F

Total 93 lots 3,971 

respirators

2 Testing was completed from 2017 – 2019. For shelf life information, refer to [3M 2018], [3M 2019], [3M 2020], [Kimberly Clark 2018], 

[Moldex 2015], [Alpha ProTech 2020]. Gerson does not designate a shelf life for the Gerson 1730 model. 3 As of March 2020, these are the current storage recommendations made by the approval holder. Refer to [3M 2020], [Gerson 2019], 

[Kimberly Clark 2020], [Alpha ProTech 2019], [Moldex 2019]. 4 For one 3M 1860 lot, only 15 respirators were used for filtration testing, and no respirators were tested against inhalation/exhalation 

resistance. Remaining respirators were saved for other tests. 5 The 3M 8000 model is no longer produced or sold by 3M.

6 3M was consulted and could not determine the manufacturing year for two lots sampled from Facility Ten and Facility Four. 7 No specific %RH recommendations.
6

Selection of Control Respirators

• Control respirators of the same model as those sampled from the ten facilities were purchased from the 

open market, tested for inhalation/exhalation resistance and filtration performance, and the results 

were compared to the stockpiled respirators. One lot of each control model was purchased. New 3M 

8000 respirators were not available to be purchased since this model is no longer produced or sold by 

3M.

• Testing was completed from 2018 to 2019. The controls had the following manufacturing dates

o 3M 1860 (size regular), 3M 2071, Moldex 2201 (size small), and Moldex 1512 (size medium): 

2018

o 3M 9010: purchased in 2018, approval holder could not verify manufacturing date

o Kimberly Clark (KC) 46727 (size regular), KC 46827 (size small), Gerson 1730, and Medline/Alpha 

ProTech NON 27501: 2017

o 3M 8210: 2015

o 3M 1870: 2014

o 3M 8000: 20068

Evaluation of Inhalation and Exhalation Resistance and Filtration Performance

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

(n=3) and filtration performance (n=20) per manufacturing lot. NIOSH testing requirements state that a 

minimum of three respirator units must be tested for inhalation and exhalation resistance and a 

minimum of 20 respirator units must be tested for filtration performance [NIOSH 2018]. For filtration 

performance, 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.

8 The 3M 8000 model is no longer produced or sold by 3M and thus new respirators were unable to be purchased. An assumption is made 

that these respirators were stored within 3M’s designated storage conditions.
7

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) 39 39

STP 7: Inhalation Resistance <35 mm H2O column @ 85 LPM 39 39

STP 53: Liquid Particulate Filter 

Efficiency for P9510

<5.0% particulate penetration 

(>95.0% filter efficiency) 4011 20

STP 59: Particulate Filter 

Efficiency for N95

<5.0% particulate penetration 

(>95.0% filter efficiency) 4011 20

Total Number of N95 FFRs tested per lot 43 23

Total Number of P95 filters tested per lot 43 23

What NIOSH Found Through Inspection, Testing, and Evaluation 

Storage Conditions

• Facility-specific findings—such as site and pallet storage conditions—can be found in the series of ten 

individual PPE CASE Reports [Greenawald et al. 2020]. 

• A brief synopsis of storage conditions found at each of the ten facilities is presented in Table 3.

• Temperature and % RH: Four facilities provided temperature and %RH records. For facilities without 

temperature and %RH records, NIOSH-provided a data logger to monitor temperature and %RH for at 

least eight months. Data points were collected from the following timeframes for each facility:

o Facility One: 2 years 11 months (facility-generated data)

o Facility Two: 2 years 11 months (facility-generated data)

o Facility Three: 1 year 4 months (NIOSH data logger-generated data)

o Facility Four: 1 year (NIOSH data logger-generated data)

o Facility Five: 1 year (NIOSH data logger-generated data)

o Facility Six: 3 years 10 months (facility-generated data)

o Facility Seven: 1 year (NIOSH data logger-generated data)

o Facility Eight: 8 months (NIOSH data logger-generated data)

o Facility Nine: 9 months (NIOSH data logger-generated data)12

o Facility Ten: 5 years (facility-generated data)

9 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.

10 This STP was used for the P95 particulate filter.

11 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.

12 Facility Nine stored products in a trailer that was outside year-round (the respirators were moved to the basement of a health 

department about one month prior to the NIOSH visit); mold was observed on and in these respirator boxes.
8

• Figures 4 and 5 show the minimum, maximum, and average temperature and %RH, respectively, for 

each of the ten collaborating stockpiles across the specified timeframe. Facility-specific temperature and 

%RH data plots over time can be found in the series of ten PPE CASE reports [Greenawald et al. 2020].

Table 3: Summary of the Storage Characteristics at the Ten Stockpile Facilities

Stockpile 

Facility Models Storage Characteristics

Environmental 

Controls and 

Monitoring

1

3M 1860

Gerson 1730

Medline/APT

Lighting off when unoccupied; no evidence of excess moisture or chemical 

spills that; no windows allowing sunlight; pallets shrink wrapped on pallets 

sides but not top or bottom; some pallets stacked two-high on the top most 

rack, causing some weight to be applied to the bottom pallet

Temperature controlled; 

temperature and %RH 

monitored.

2 3M 1860

Gerson 1730

Warehouse shared with another entity; lighting off when unoccupied; no 

evidence of excess moisture or chemical spills; no windows allowing sunlight; 

pallets shrink wrapped on pallets sides but not top or bottom; pallets 

separated by metal rack.

Temperature controlled; 

temperature and %RH 

monitored.

3 3M 1860

KC 46727

Products stored outside of original case packaging and in plastic containers; 

products were not on pallets; lighting off when unoccupied; no evidence of 

excess moisture or chemical spills; no windows allowing sunlight; no dust was 

observed on the respirator boxes stored inside or on top of the containers. 

Some dust settled on the top-most layer of cases in the instances where no 

shrink wrap or heavy plastic was applied to the top of the pallet.

Temperature only recently 

controlled but not controlled 

for most of the products’ 

storage life; temperature and

%RH not monitored.

4

3M 1860

3M 1870

3M 2071

3M 8210

3M 9010

KC 46827

Lighting off when unoccupied; small ceiling vents allowed sunlight to enter 

facility; no evidence of excess moisture or chemical spills n; pallets shrink 

wrapped on pallets sides but not top or bottom; some pallets stacked twohigh on the top most rack, causing some weight to be applied to the bottom 

pallet.

Temperature controlled; 

temperature and %RH not 

monitored.

5

3M 1860

3M 1870

3M 2071

3M 8210

3M 9010

KC 46827

Lighting off when unoccupied; ceiling skylights allowed sunlight to enter 

facility and shine on PPE pallets; no evidence of excess moisture or chemical 

spills; pallets shrink wrapped on pallets sides but not top or bottom; generally, 

all pallets stacked three (or more)-high, causing some weight to be applied to 

the bottom pallet.

No controls or monitoring.

6

3M 8000

KC 46727

KC 46827

Moldex 2201

Lighting off when unoccupied; no evidence of excess moisture or chemical 

spills; no windows allowing sunlight; ceiling fans circulated air; pallets shrink 

wrapped on pallets sides and the top; pallets separated by metal rack.

Temperature and %RH 

controlled; temperature and 

%RH intermittently 

monitored.

7

3M 1860

3M 1870

3M 8000

3M 9010

KC 46727

KC 46827

Lighting off when unoccupied; no evidence of chemical spills; evidence of

mitigated moisture damage on facilities walls; some windows allowed indirect 

sunlight; pallets shrink wrapped on sides and a plastic covering was placed on 

the top; pallets separated by metal rack.

No controls or monitoring.

8

3M 1860

3M 8000

KC 46727

KC 46827

Moldex 1512

Lighting off when unoccupied; no evidence of excess moisture or chemical 

spills; pallets shrink wrapped on pallets sides and the top though many PPE 

products were not on pallets nor shrink wrapped; some pallets separated by 

metal rack and others stacked two-high, causing some weight to be applied to 

the bottom pallet.

Temperature controlled; 

temperature intermittently 

monitored.

9 KC 46727

KC 46827

Stockpile manager reported that products were stored in a trailer for at least 

seven years; trailer was stored outside at all times; PPE was stored outside of 

original case packaging; products were not on pallets; lighting off when 

unoccupied; no evidence of excess moisture or chemical spills; no windows 

allowing sunlight

No controls or monitoring.

10

3M 1860

3M 8000

3M 8210

Gerson 1730

KC 46827

Lighting off when unoccupied; no evidence of excess moisture or chemical 

spills; no windows allowing sunlight; pallets shrink wrapped on sides but not 

top or bottom; pallets separated by metal rack.

Temperature controlled; 

temperature and %RH 

monitored.
9

• Respirator Box and Respirator Visual Inspections—Visual inspection concerns were recorded for factors 

that may affect respirator performance. These included crushing to the respirator box, damage to the 

respirator (including the nose bridge or straps), and/or the appearance of mold. Examples of visual 

inspection concerns for respirator boxes and individual respirators are provided in Figure 3. Overall, 

stockpiled respirators were sampled from 339 boxes; 36 boxes (10.6%) showed some level of damage 

(e.g., crushing, appearance of mold). Ninety-nine respirator visual inspection concerns were noted for 66 

out of the 3,971 total respirator units individually inspected (i.e., 1.7% of the respirator units inspected 

included visual inspection concerns).

Figure 3: Examples of visual inspection concerns to the respirator box and individual respirator units including A) 

box damage; B) dust; C) strap damage to respirator and mold on respirator box; D) damage to respirator nose 

bridge (here, the respirator is fixed to test plate); E) damage to respirator nose foam; and F) crushing of the 

respirator unit itself.
10

Figure 4: Average, minimum, and maximum temperature across all ten stockpile facilities visited in this study.

HHS regions for each facility are also depicted; refer to Figure 1 for the HHS region locations.

Figure 5: Average, minimum, and maximum %RH across all ten stockpile facilities visited in this study. HHS 

regions for each facility are also depicted; refer to Figure 1 for the HHS region locations.
11

Inhalation and Exhalation Resistance

• NIOSH evaluated the inhalation and exhalation resistance for a total of 276 stockpiled and 36 control 

respirators. All stockpiled and control respirators from each model passed these tests. The aggregated 

inhalation/exhalation resistance data for the 3M models can be seen in Figure 6; the aggregated 

inhalation/exhalation resistance data for the KC, Gerson, Moldex, and Medline/Alpha ProTech models 

can be seen in Figure 7.

• The 99% confidence interval for inhalation and exhalation resistance is shown in the figures. The upper 

bounds of each of the 99% confidence intervals are well within the NIOSH minimum performance 

requirements.
12

Figure 6: Mean control and stockpiled (SP) respirator inhalation (A) and exhalation (B) resistance data

for the 3M 1860, 3M 1870, 3M 2071, 3M 8000, 3M 8210, and 3M 9010 models. APRs 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. The number of stockpiled units tested is shown under the model name.
13

Figure 7: Mean control and stockpiled (SP) respirator inhalation (A) and exhalation (B) resistance data

for the Gerson 1730, KC 46727, KC 46827, Medline/Alpha ProTech NON27501 (Medline/APT), Moldex 

1512, and Moldex 2201 models. APRs 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. The number of 

stockpiled units tested is shown under the model name.
14

Filtration Performance

• NIOSH evaluated the particulate penetration efficiency for 3,695 stockpiled respirators and 240 control 

respirators (i.e., 20 for each of the 12 respirator models). The aggregated filtration efficiency data for 

the 3M 1860, 3M 1870, 3M 8000, 3M 8210, and 3M 9010 models can be seen in Figure 8. The 

aggregated filtration efficiency data for the 3M 2071 model (the only P95 model in the study) can be 

seen in Figure 9. The aggregated filtration efficiency data for the Gerson 1730, KC 46727, KC 46827, 

Medline/Alpha ProTech, Moldex 1512, and Moldex 2201 models can be seen in Figure 10.

• Seventy-six N95 FFRs did not meet NIOSH performance standards, accounting for 2% of the total 

respirators tested to particulate N95 filtration performance. No liquid particulate (P95) filtration failures

were observed.

• The respirators that failed came from three different stockpiles and three different N95 FFR models: 3M 

1860, KC 46727, and KC 46827. In Facility Three, one 3M 1860 respirator failed from a lot manufactured 

in 2006, and one respirator failed from a lot that was manufactured in 2009. All other units tested from 

this facility passed. In Facility Four, 34 (42.5%) of the 80 KC 46827 units tested from two different lots 

(both manufactured in 2007) failed. In Facility Seven, all 40 (100%) of the KC 46727 respirators tested 

from one lot manufactured in 2007 failed. The other units tested from these facilities passed. These 

three models currently have a five-year designated shelf life. 

• The 99% confidence interval for filtration performance is shown in the figures. The upper bounds of the 

99% confidence intervals for all stockpiled respirators were no more than 60% of NIOSH’s maximum 

permissible level of penetration.

• Lot-specific results can be found in the series of ten PPE CASE reports [Greenawald et al. 2020].

• The failing units were not associated with any respirator visual inspection concerns (i.e. no damage to 

the respirator, straps, or metal nose bridge was observed). One failing unit (the 3M 1860 unit from 

Facility Three) came from a box with slight crushing to the bottom.

• A summary of the visual inspection and overall pass/fail data for each stockpile is shown in Table 4. A 

footnote is included for those models that do not currently have a designated shelf life, which were the 

Gerson 1730 and the Alpha ProTech NON27501 [Appendix 1]; all other models currently have a 

designated shelf life. A summary of the respirator performance data for each stockpile is shown in Table 

5

• Figure 11 depicts the number of passing and failing units for each model sampled across the 10 facilities 

when considering only filtration performance. The failing units were not associated with visual 

inspection concerns to the respirator.
15

Figure 8: Mean control and stockpiled (SP) respirator particle filtration performance data for the 3M 1860, 3M 

1870, 3M 8000, 3M 8210, and 3M 9010 models. 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. The number of stockpiled units tested is shown under the model name.
16

Figure 9: Mean control and stockpiled (SP) respirator particle filtration performance data for the 3M 2071 

model. P95 filters 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. The number 

of units tested is shown under the model name.
17

Figure 10: Mean control and stockpiled (SP) respirator particle filtration performance data for the Gerson 1730, 

KC 46727, KC 46827, Medline/Alpha ProTech NON27501 (Medline/APT), Moldex 1512, and Moldex 2201 

models. 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. The number 

of stockpiled units tested is shown under the model name.
18

Table 4: Summary of Visual Inspection Concerns and the Pass/Fail Data for Each Stockpile Facility; Asterisks 

Indicate Which Production Lot (Indicated by The Manufacturing Year) the Failing Units Came From

Stockpile Facility

Model (Manufacturing Year of Sampled Lot[s])

Visual Inspection Concerns to Box or 

Respirator

% of Respirators with Visual Inspection Concerns 

to the Unit or the Box THAT STILL PASSED NIOSH 

Performance Requirements

Stockpile Facility One

• Gerson 173013 (2006, 2006)

• 3M 1860 (2008, 2008, 2009, 2009)

• Alpha ProTech NON2750113,14(2008, 2008)

1 respirator crushed, 3 boxes with slight 

damage to corner

100% Passed

Stockpile Facility Two

• Gerson 173013 (2006)

• 3M 1860 (2006, 2006, 2008, 2008, 2009, 2009)

12 respirators with nose foam concerns 100% Passed

Stockpile Facility Three

• 3M 1860 (2006*, 2006, 2009*, 2009)

• KC 46727 (2006, 2006)

5 boxes with slight crushing at the 

bottom; 1 nose foam concern

99.2% Passed

1 unit (2%) failed of the 50 units that were tested 

from the 5 boxes with slight crushing

Stockpile Facility Four

• 3M 1860 (2006, 2010, 2010)

• KC 46827 (2007, 2007*, 2007*)

• 3M 1870 (2010, 2010)

• 3M 8210 (2006, year not available)15

• 3M 9010 (2006, 2006)

• 3M 2071 (2006, 2006)

9 boxes with slight crushing near the 

bottom or sides

94.1% passed

Stockpile Facility Five

• 3M 1860 (2007, 2007, 2010, 2010)

• KC 46827 (2006, 2006)

• 3M 1870 (2011, 2011)

• 3M 8210 (2006, 2006)

• 3M 9010 (2006, 2006)

• 3M 2071 (2006, 2006)

0 100% Passed

Stockpile Facility Six

• KC 46727 (2006, 2006)

• KC 46827 (2007, 2007)

• Moldex 2201 (2006, 2006)

• 3M 8000 (2006, 2006, 2006)16

0 100% Passed

Stockpile Facility Seven

• 3M 1860 (2007, 2007, 2010, 2010)

• 3M 1870 (2013)

• 3M 8000 (2008, 2008)14

• KC 46727 (2006, 2007*)

• KC 46827 (2006, 2007)

• 3M 9010 (2007, 2007)

0 92.8% Passed

Stockpile Facility Eight

• 3M 1860 (2007, 2007)

• 3M 8000 (2006, 2006)16

• KC 46727 (2006)

• KC 46827 (2006)

• Moldex 1512 (2009, 2009)

3 boxes with crushing to the right side and 

opened 100% Passed

Stockpile Facility Nine

• KC 46727 (2003, 2003)

• KC 46827 (2003, 2003)

12 boxes with crushing, mold concerns, 

and dust; 33 respirators had nose bridge 

damage, 43 respirators had mold 

concerns, 9 straps had damage

100% Passed

Stockpile Facility Ten

• 3M 1860 (2006, 2006)

• KC 46827 (2006, 2007)

• 3M 8000 (2006, 2006)16

• 3M 8210 (two lots sampled; years not available)

15

• Gerson 173013 (2006, 2006)

4 boxes with crushing to the top 100% Passed

13 Model does not currently have a designated shelf life by the approval holder.

14 The FFR model NON27501 has been manufactured by Alpha ProTech as a private label to Medline under TC-84A-0457. 15 3M was consulted and could not determine the manufacturing year of these two lots tested. 16 The 3M 8000 is no longer produced or sold by 3M.
19

Table 5: Summary of the Respirator Performance for Units Sampled from the Ten Stockpiles; Asterisks Indicate 

Which Production Lot (Indicated by The Manufacturing Year) the Failing Units Came From

Stockpile Facility

Model (Manufacturing Year of Sampled 

Lot[s])

# of Respirators Tested to Inhalation and 

Exhalation Resistance 

(# of Failures)

# Respirators Tested to Particulate 

Filtration Efficiency

(# of Failures)

Stockpile Facility One

• Gerson 173017 (2006, 2006)

• 3M 1860 (2008, 2008, 2009, 2009)

• Alpha ProTech NON2750118(2008, 2008)

24 (0) 320 (0)

Stockpile Facility Two

• Gerson 173011 (2006)

• 3M 1860 (2006, 2006, 2008, 2008, 2009, 2009)

21 (0) 280 (0)

Stockpile Facility Three

• 3M 1860 (2006*, 2006, 2009*, 2009)

• Kimberly Clark (KC) 46727 (2006, 2006)

18 (0) 240 (2*)

Stockpile Facility Four

• 3M 1860 (2006, 2010, 2010)

• KC 46827 (2007, 2007*, 2007*)

• 3M 1870 (2010, 2010)

• 3M 8210 (2006, year not available)19

• 3M 9010 (2006, 2006)

• 3M 2071 (2006, 2006)

39 (0) 535 (34*)

Stockpile Facility Five

• 3M 1860 (2007, 2007, 2010, 2010)

• KC 46827 (2006, 2006)

• 3M 1870 (2011, 2011)

• 3M 8210 (2006, 2006)

• 3M 9010 (2006, 2006)

• 3M 2071 (2006, 2006)

42 (0) 560 (0)

Stockpile Facility Six

• KC 46727 (2006, 2006)

• KC 46827 (2007, 2007)

• Moldex 2201 (2006, 2006)

• 3M 8000 (2006, 2006, 2006)20

27 (0) 360 (0)

Stockpile Facility Seven

• 3M 1860 (2007, 2007, 2010, 2010)

• 3M 1870 (2013)

• 3M 8000 (2008, 2008)20

• KC 46727 (2006, 2007*)

• KC 46827 (2006, 2007)

• 3M 9010 (2007, 2007)

39 (0) 520 (40*)

Stockpile Facility Eight

• 3M 1860 (2007, 2007)

• 3M 8000 (2006, 2006)20

• KC 46727 (2006)

• KC 46827 (2006)

• Moldex 1512 (2009, 2009)

24 (0) 320 (0)

Stockpile Facility Nine

• KC 46727 (2003, 2003)

• KC 46827 (2003, 2003)

12 (0) 160 (0)

Stockpile Facility Ten

• 3M 1860 (2006, 2006)

• KC 46827 (2006, 2007)

• 3M 8000 (2006, 2006)20

• 3M 8210 (two lots sampled; years not 

available)

19

• Gerson 173011 (2006, 2006)

30 (0) 400 (0)

17 Model does not currently have a designated shelf life by the approval holder.

18 The FFR model NON27501 has been manufactured by Alpha ProTech as a private label to Medline under TC-84A-0457. 19 3M was consulted and could not determine the manufacturing year of these two lots tested.

20 The 3M 8000 is no longer produced or sold by 3M.
20

Figure 11: Summary of the stockpiled respirators tested for filtration efficiency performance from twelve APR 

models, as well as the total stockpiled respirators tested for filtration efficiency performance across the ten 

facilities. White represents the number of passing respirators and the black lines represents the number of 

failing respirators for each model.
21

CASE Findings

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 holder21 (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 primary application for the FFRs included in this study is to be a 

near-immediate use item that is both low-cost and single-use. The design and material selection for this primary 

application may not always align with secondary applications such as stockpiling where long-term product 

viability is required. 

Findings for Respirator and Box Visual Inspections

• Overall, <2% of the total respirators visually inspected had visual inspection concerns, which included 

the respirators’ nose foam sticking to adjacent respirators within the box, crushing, mold, and damage 

to straps. As seen in Table 4, no trends were observed between respirators with visual inspection 

concerns and performance—i.e. all 66 respirator units associated with visual inspection concerns met 

NIOSH’s minimum performance requirements. Thirty-six boxes showed signs of damage, including 

crushing to the sides, mold, and signs of water damage.

Findings for Inhalation Resistance, Exhalation Resistance, and Filtration Performance

• NIOSH found that 3,895 out of the 3,971 APRs evaluated in this study maintained their inhalation and 

exhalation resistance and filtration performance (i.e., 98% of the sampled respirators were within the 

NIOSH performance limits as defined by 42 CFR Part 84). 

• No failures were identified for the 276 stockpiled respirators tested against inhalation resistance or 

exhalation resistance. 

• A total of 3,619 out of 3,695 (i.e., 98%) passed filtration performance across ten facilities with conditions 

that both met and deviated from recommended storage conditions. The upper bounds of each of the 

99% confidence intervals for each test are well within the NIOSH minimum performance requirements.

One of 3,695 respirators units (0.03%) that failed filtration performance from a box with damage. No 

failures were associated with respirators that) showed signs of damage to the unit itself. This one failing 

unit came from a box with damage (i.e., slight crushing to the bottom of the box). Thus, no 

trend/relationship was observed between filtration performance and visual inspection concerns of the 

box or respirator unit itself.

o Filtration Performance Findings for the 3M Models

 3M 1860 – 1,135 units were tested from eight facilities. 99.99% of units passed.

 3M 1870 – 200 units were tested from three facilities. 100% of units passed.

 3M 8000 – 360 units were tested from four facilities. 100% of units passed.

21 An approval may be granted to a non-manufacturing entity.
22

 3M 8210 – 240 units were tested from three facilities. 100% of units passed.

 3M 9010 – 240 units were tested from three facilities. 100% of units passed.

 3M 2071 – 160 units were tested from two facilities. 100% of units passed.

o Filtration Performance Findings for the Gerson Model

 Gerson 1730 – 200 units were tested from three facilities. 100% of units passed.

o Filtration Performance Findings for the Kimberly Clark Models

 Kimberly Clark 46727 – 360 units were tested from five facilities. 89.66% of units passed.

 Kimberly Clark 46827 – 560 units were tested from five facilities. 94.35% of units passed.

o Filtration Performance Findings for the Medline/Alpha ProTech Model

 Medline/Alpha ProTech NON27501 – 80 units were tested from one facility. 100% of 

units passed.

o Filtration Performance Findings for the Moldex Models

 Moldex 1512 – 80 units were tested from one facility. 100% of units passed.

 Moldex 2201 – 80 units were tested from one facility. 100% of units passed.

• All stockpiled respirators tested that had a designated shelf life by the approval holder were past their 

shelf lives at the time of testing [Kimberly Clark 2018, Appendix 2]; [3M 2018, 3M 2020, Appendix 3]; 

[Moldex 2015, Appendix 4]. 

• Regarding the Kimberly Clark filtration failures, The Kimberly Clark 46727 model was stockpiled in five of 

the ten facilities, and the Kimberly Clark 46827 was stockpiled in seven of the ten facilities. The failing 

Kimberly Clark 46827 units were stockpiled in Facility Four, where 25 failures came from one production 

lot, and 9 failures came from a different production lot. Both lots were manufactured in 2007. A third 

Kimberly Clark 46827 lot, also manufactured in 2007, was sampled from Facility Four, where all units 

passed. The failing Kimberly Clark 46727 units came from Facility Seven, where all failures came from 

one production lot manufactured in 2007. A second Kimberly Clark 46827 lot, manufactured in 2006, 

was sampled from Facility Seven, where all units passed. All failing units were inspected, and no visual

inspection concerns to the respirator or adherence to the test plate during testing were identified. In 

2018, Kimberly Clark released a communication to end users reminding them of the five-year shelf life 

for these models and that units should be disposed of after they have reached their shelf life [Kimberly 

Clark 2018, Appendix 2]. The approval holder noted that the most likely cause of the test penetration 

failure was due to material changes over time and recommended that units beyond these models’ fiveyear shelf life be disposed [Kimberly Clark 2018].

• Regarding the 3M 1860 filtration failures, these units were stockpiled in Facility Three, where one unit 

came from a production lot manufactured in 2006, and the other unit came from a production lot 

manufactured in 2009. All failing units were inspected, and no visual inspection concerns to the 

respirator or adherence to the test plate during testing were identified. These units were past the 

designated shelf life [3M 2018, 3M 2020, Appendix 3]. Two additional 3M 1860 lots were sampled from 

Facility Three, where all units passed. 
23

The high replacement cost for large quantities of respirators (and other types of PPE) results in most stockpiles 

relying on federal resources during public health emergencies to replenish inventory. The temporal infrequency 

of large-scale public health emergencies suggests that shelf life issues will be an ongoing consideration for 

managing stockpiled respirators. While the results of this study significantly inform levels of protection that may 

be provided by respirators that have been stored for long periods in U.S. stockpiles, the results may not be 

applicable to other respirator models or stockpile facilities. Although the general trend observed in this study is 

that the majority of respirators evaluated would be protective across a variety of storage conditions, important 

variability was observed. For example, respirator units sampled from select production lots of a particular model 

demonstrated the ability to be protective while units from a different lot of the same model, stored in the same 

facility, are shown to not be protective. Furthermore, select models are demonstrated to be protective when 

sampled from one facility but not from another with similar conditions and years of storage. 

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

provided by all 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. 

However, based on the results of this study, on February 19, 2020 CDC/NIOSH issued guidance related to 

stockpiled FFRs: Release of Stockpiled N95 Filtering Facepiece Respirators beyond the Manufacturer-Designated 

Shelf Life: Considerations for the COVID-19 Response [CDC 2020a]. The summary of this guidance states:

• N95s that are past their manufacturer-designated shelf life are no longer considered NIOSH-approved, 

as all manufacturer-designated conditions of use must be met to maintain the NIOSH approval. 

• In times of increased demand and decreased supply, consideration can be made to use the following

N95s past their manufacturer-designated shelf life when responding to the 2019 novel coronavirus

(COVID-19). These models that were tested in NIOSH’s study continued to perform in accordance with 

NIOSH performance standards for filtration efficiency and inhalation/exhalation resistance:

o 3M 1860

o 3M 1870

o 3M 8210

o 3M 9010

o 3M 8000

o Gerson 1730

o Medline/Alpha ProTech NON27501

o Moldex 1512

o Moldex 2201

• Although the preliminary information outlined from NIOSH’s study suggests certain N95 models beyond 

their manufacturer-designated shelf life22 will be protective, CDC/NIOSH recommends that N95s that 

have exceeded their manufacturer-designated shelf life should be used only as outlined in the Strategies 

for Optimizing the Supply of N95 Respirators [CDC 2020b]. 

22 The Gerson 1730 and the Medline/Alpha Protech NON27501 models do not have a manufacturer-designated shelf life. All 

other models included in the study exceeded their manufacturer-designated shelf life.
24

Users provided any of these products 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 NIOSH approval holder(s) of the respirators in the stockpile with specific questions 

regarding the use of product beyond the designated shelf life.

Stockpile personnel have reported needing uniform guidance related to inventory management for respirators 

that are past their shelf life designated by the approval holder. Ideally, stockpiles would continuously rotate 

products with local hospitals or other entities to ensure products are within their shelf life. However, the current 

reality is that facilities across the U.S. have respirators (and other types of PPE) stored that are over five years 

old, most exceeding their designated shelf life. One path forward is to develop and implement an economically 

sustainable stockpile quality assurance process where stockpiles from around the nation test and evaluate their 

respirator inventories with the results being shared with product manufactures to optimize shelf life 

designations. The quantitative testing should demonstrate conformance to NIOSH’s minimum performance 

requirements. In addition to optimizing shelf life designations, NIOSH recommends a national stockpile 

maintenance approach to purchase, store, and deploy respirators (e.g., rotate inventory) to ensure respirator 

availability and product usage within these optimized shelf lives. 
25

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 stockpiles 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. 
26

Suggested Citation 

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

Respirators: Overall Performance of Nearly 4,000 Respirators Sampled from Ten Stockpile Facilities. By Greenawald, L., 

Moore, S., and Yorio, P.L. 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 P2020-0111. 

References

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. Accessed 03/09/2020. (Also

in Appendix 3) 

3M [2019]. Email correspondence with 3M representatives. November 2019.

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. Accessed 03/09/2020. (Also in Appendix 3) 

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

Alpha ProTech [2020]. Shelf Life/Expiration Dating. (Also in Appendix 1). 

ASTHO [2013]. Federal Emergency Preparedness Directives and Systems- Emergency Authority and Immunity Toolkit.

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/. Accessed 03/09/2020.

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.

CDC [2020a]. Release of Stockpiled N95 Filtering Facepiece Respirators Beyond the Manufacturer-Designated Shelf Life:

Consideration for the COVID-19 Response. https://www.cdc.gov/coronavirus/2019-ncov/release-stockpiled-N95.html. 

Accessed 03/09/2020.

CDC [2020b]. Strategies for Optimizing the Supply of N95 Respirators. https://www.cdc.gov/coronavirus/2019-

ncov/hcp/respirators-strategy/index.html. Accessed 03/09/2020.

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

Washington D.C: U.S. Department of Health and Human Services, https://www.phe.gov/Preparedness/mcm/h1n1-

retrospective/Documents/h1n1-retrospective.pdf. Accessed 03/09/2020.

Gerson [2019]. Gerson Customer Service, email correspondence, October 1, 2019.

Greenawald, L.A.; Moore, S.M.; Yorio, P. [2020]. Ten PPE CASE Reports: Performance of Stockpiled Air-Purifying Respirators.

https://www.cdc.gov/niosh/npptl/ppecase.html. Accessed 03/09/2020.

Kimberly Clark [2018]. Kimberly Clark Letter to Customers. (Also in Appendix 2). 

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

NIOSH [1997]. 42 CFR Part 84 respiratory protective devices. Cincinnati, OH: U.S. Department of Health and Human

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

https://www.cdc.gov/niosh/npptl/topics/respirators/pt84abs2.html. Accessed 03/09/2020.

Moldex [2015] Moldex Memo to Customers and Distributors (Also in Appendix 4).
27

Moldex [2019]. Moldex Customer Service Representative, personal communication through email, October 31, 2019.

NIOSH [2017]. Workplace safety and health topics: healthcare workers. Cincinnati, OH: U.S. Department of Health and 

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

https://www.cdc.gov/niosh/topics/healthcare/default.html. Accessed 03/09/2020.

NIOSH [2018]. Standard respirator testing procedures. Cincinnati, OH: U.S. Department of Health and Human Services, 

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

https://www.cdc.gov/niosh/npptl/stps/apresp.html. Accessed 03/09/2020.

NIOSH [2019]. NIOSH conformity assessment notice: NIOSH CA 2019-1012, NIOSH respirator approval contents and 

meaning. Pittsburgh, PA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, 

National Institute for Occupational Safety and Health, 

https://www.cdc.gov/niosh/npptl/resources/pressrel/letters/conformitynotice/CA-2019-1012.html. Accessed 03/09/2020.

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

chain: lessons learned from recent public health emergency responses. Health Security. 15 (3): 244-252 

https://doi.org/10.1089/hs.2016.0129. 

Rottach DR, Lei Z [2017] Stockpiled N95 filtering facepiece respirator polyisoprene strap performance. J Int Soc Respir Prot.

34 (2): 69-80 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6198819/.
28

Appendix 1 [Alpha ProTech 2020]
29

Appendix 2 [Kimberly Clark 2018]
30

Appendix 3 [3M 2018], [3M 2020]
31
32
33
34
35
36

Appendix 4 [Moldex 2015]