PPE CASE

Personal Protective Equipment Conformity Assessment Studies and Evaluations

Evaluation of Fit and Strap Extension Performance of Stockpiled Filtering 

Facepiece Respirators from One U.S. Facility

National Institute for Occupational Safety and Health (NIOSH)

National Personal Protective Technology Laboratory (NPPTL)

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

November 3, 2021

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

healthcare workers may face exposure to high-consequence 

infectious disease [NIOSH 2017]. Personal protective equipment 

(PPE), such as gowns, gloves, goggles, and respirators, is an 

important control 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]. Recent outbreaks—even those 

that occurred without extensive impact on US operations (e.g., 2009 

H1N1 pandemic, 2016 Ebola outbreak)—caused respirator 

shortages; when the first U.S. fatality was reported during the Ebola 

outbreak, the PPE orders increased 10-200 fold [CDC 2021; DHHS 2012; NIOSH 2018]. To prepare for these surge 

demands, emergency planners stockpile large quantities of PPE at federal and state levels to support local 

supplies [Patel et al. 2017]. At the onset of this study in 2017, these products had been stored for more than five 

or even ten years. NIOSH-approved N95 filtering facepiece respirators (FFRs) are commonly used particulateonly air-purifying respirators (APRs) by many healthcare facilities so they are a commonly stockpiled product. 

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 (APRs), including FFRs. However, some approval holders have 

assigned a shelf life to the FFRs that they produce as indicated by product packaging or online reference 

materials. Additionally, NIOSH minimum performance requirements found within Title 42, Code of Federal 

Regulations, Part 84 do not require an assessment of fit as part of the evaluation. However, under its 

Respiratory Protection Standard (29 CFR 1910.134), the Occupational Safety and Health Administration (OSHA) 

requires employers to fit test any workers using tight-fitting respirators, including FFRs, prior to initial use of the 

respirator, whenever a different respirator facepiece (size, style, model or make) is used, and at least annually 

thereafter [OSHA 2021]. OSHA also requires employers to ensure that workers using tight-fitting respirators

perform a user seal check each time they put on the respirator [OSHA 2021]. 

Over the past decade, the Strategic National Stockpile (SNS) and state and local stockpile personnel asked NIOSH 

to evaluate the effect of stockpile conditions on the viability of respirators. To support this request, NIOSH 

collected samples of stockpiled N95 FFRs from ten geographically dispersed facilities with varying storage 

NIOSH evaluated 293 stockpiled 

N95 filtering facepiece respirators 

(FFR) from a single facility to 

determine if long-term storage (9-

13 years) affected fit. Using 

human subjects, quantitative fit 

testing identified product- and lotspecific differences between the 

control and stockpiled 

respirators—substantial 

differences were detected for 

some products.
2

conditions from 2017-2019. Approximately 4,000 FFRs were collected and tested in accordance with NIOSH 

performance requirements. The facility-specific reports can be found here.

This report details the fit testing performance of N95 FFRs collected from Facility Four which is one of the ten

facilities visited. Facility Four is a state stockpile facility.

How NIOSH Evaluated Respirators and Storage Conditions

Description of Facility Four

• NIOSH researchers visited Facility Four in March 2018. This facility was located within the U.S. 

Department of Health and Human Services Region 9, representing Arizona, California, Hawaii, and 

Nevada. Respirators from Stockpile Four were chosen to evaluate for fit out of the ten stockpile facilities 

due to the various models of NIOSH-approved N95 FFRs that were available for sampling compared to 

some of the other facilities in this study.

Assessment of Storage Conditions

• For a full description of Facility Four storage conditions, refer to “Facility Four of Ten: Inhalation and 

Exhalation Resistance and Filtration Efficiency Performance” [Greenawald et al. 2020]. Briefly, 

temperature and percent relative humidity (%RH) data were obtained for one year prior to samples 

being collected and NIOSH documented the following storage conditions: 1) the presence of dust on PPE 

packaging, use of shrink-wrapping, potential for exposure to chemicals and moisture; 2) potential for 

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 load-bearing, bottom/load-bearing).

Collection of Respirator Samples

• Samples were collected from five different manufacturing models1

: 1) 3M 1860 (two manufacturing 

years); 2) 3M 1870; 3) 3M 8210; 4) 3M 9010; and 5) Kimberly Clark (KC) 46827 (Table 1). 

• Detailed inventories and storage location by lot within Facility Four were reviewed. At a minimum, two 

manufacturing lots for each model were identified and sampled within Facility Four to consider inter-lot 

variation. For models with lots stored in a variety of conditions throughout the facility, one or two

additional lots were sampled to reflect the range of storage conditions observed. Samples were 

collected from the stockpile and shipped to the NIOSH facility overnight to reduce exposure to nonclimate-controlled conditions. 

• A minimum of 25 respirators from each manufacturing lot were collected for fit testing.

Selection of Control Respirators

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

market and used for comparison to stockpiled respirators.

• The 3M 1860 controls were manufactured in 2018. The 3M 8210 controls were manufactured in 2015.

The 3M 1870 controls were manufactured in 2014. The 3M 9010 controls were purchased in 2018, but 

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

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

the researchers were not able to determine the manufacturing date from the product packaging. The KC 

46827 controls were manufactured in 2017. 

Characteristics of Sampled Respirators

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

Table 1. FFRs Collected from Stockpile Facility Four

Model Lot # Year of 

Manufacture

Shelf Life on 

Packaging?

Respirator Age at Time of 

Testing2

Shelf Life 

Status at Time 

of Testing

3M 1860 Lot A 2010 No 9 years

Past 5-year shelf 

life3

3M 1860 Lot B 2010 No 9 years Past 5-year shelf 

life3 3M 1860 Lot C4 2006 No 13 years

3M 18705 Lot A 2010 No

9 years

Past 5-year shelf 

life3 3M 18705 Lot B 2010 No

3M 8210 Lot A 2006 No

13 years

Past 5-year shelf 

life3 3M 8210 Lot B 2006 No

3M 9010 Lot A 2006 No

13 years

Past 5-year shelf 

life3 3M 9010 Lot B 2006 No

KC 46827 Lot A 2007 No

12 years

Past 5-year shelf 

life6 KC 46827 Lot B 2007 No

KC 46827 Lot C 2007 No

Evaluation of Fit

• The collected FFRs were quantitatively fit tested using the OSHA-accepted ambient aerosol 

condensation nuclei counter (CNC) quantitative fit testing protocol specified in Appendix A of OSHA’s 

Respiratory Protection standard (29 CFR 1910.134) [OSHA 2011] and human subjects7 to assess if there 

was a difference in fit between the control and stockpiled respirators. 

• Using face length and width, NIOSH’s Bivariate panel (NIOSH Panel) [NPPTL 2019] was used to classify 

the test subjects into one of ten possible panel cells—i.e., face dimension categories. Test subject panel 

cell sizes from cell sizes 1 – 10 were used regardless of respirator model size (e.g., Small, Regular).

• An attempt was made to recruit test subjects that reflected a variety of facial dimensions (i.e., panel 

cells 1 – 10) for every lot tested. Therefore, each FFR model in Facility Four (i.e., 3M 1870, 3M 8210, 3M 

9010, 3M 1860, and KC 46827) was tested using subjects with varying face shapes and sizes. 

• Twenty-five volunteers were fit tested for the new (i.e., control) respirators from each model and the 

stockpiled respirators, where each test subject donned and fit tested with the same respirator four 

times. A successful user seal check was conducted prior to fit testing each respirator that was donned.

2 Fit testing was completed in 2019.

3 3M designated a five-year shelf life for these models [3M 2018]. As of February 2021, these models still have a five-year shelf life. 4 Only one lot of the 3M 1860 manufactured in 2006 was available for sampling.

5 The 3M 1870 is no longer produced or sold by 3M and has been replaced by the 3M 1870+. 6 KC designated a five-year shelf life for this model [Kimberly Clark 2018]. As of February 2021, this model still has a five-year shelf life. 7 NIOSH IRB Protocol 18-NPPTL-01XP.
4

• A PortaCount® (Model: Pro+ Model 8038, TSI, Inc.) was used to perform fit testing and calculate

individual and overall fit factors (FFs) according to OSHA’s ambient aerosol condensation nuclei counter 

(CNC) quantitative fit testing protocol [OSHA 2021]. The N95 CompanionTM mode of the PortaCount®

was used to eliminate the bias of particulate penetration through the filter media, and only include the 

particulate leakage at the seal. In N95 CompanionTM mode, the PortaCount® measures only negatively 

charged 40-60 nm size particles, i.e., those shown to be efficiently captured by electrostatic filter media

[Rengasamy et al 2012]. The PortaCount® limits the maximum achievable FF to 200.

• The objective was to fit test 25 respirators per lot, though minor deviations occurred due to subjects 

dropping out of the study or straps breaking. The analysis considered a FF >100 as a passing test since

OSHA 29 CFR 1910.134 [OSHA 2021] requires a FF of 100 or greater during individual fit testing using the 

PortaCount®. Each subject performed the OSHA-accepted 8-exercise fit test,

8 where individual FF from 

each exercise (with the exclusion of the “grimace” exercise) were used to calculate an overall FF [OSHA 

2011]. Doffing and re-donning was conducted between fit tests.

• Three metrics were used to assess fit: 

o Mean overall FF: Calculated for each model by using each of the subject’s overall FF per 

donned respirator. The purpose of using this metric was to compare the continuous FF

values between stockpiled lots and the controls without converting to pass/fail in relation to 

OSHA’s passing value of 100. These FFs ranged from 0 – 200 and analyzing them in their 

continuous form communicates the average degree of fit observed for each lot. It also 

allows comparisons between lots with average FF scores below 100 but with important FF 

differences (e.g., an average FF close to 10 vs. an average FF of close to 100). In its 

continuous form, the FFs were analyzed using Analysis of Variance (ANOVA). 

o Donning proportion passing rate: Calculated by dividing the number of donnings out of 

total donnings that yielded an overall FF >100. Converting the continuous FF scores to pass/ 

fail (or 0s and 1s) provided the ability to conduct a z-test and analyze the difference of the 

percent of donnings that received a FF>100 between lots.

o Subject proportion passing rate: Calculated by dividing the number of subjects that yielded 

an overall FF >100 on any one of their donnings. This provided the ability to conduct a z-test 

and analyze the differences of the percent of subjects that received a FF>100 between lots.

Evaluation of Strap Extension Performance

• To further explore factors that could influence fit of stockpiled respirators, the average strap extension 

(before and after adding a weight to the strap) of ten straps per manufacturing lot were compared to 

the controls of the same model. This evaluation was done to see if differences in strap characteristics for

new and stockpiled respirators showed trends related to changes in fit (e.g., determine if looser straps 

could be associated with lower fit factors and thus poorer fit). Using a simplified test briefly described in 

Appendix 1, ten straps per manufacturing lot were compared to the controls to determine if the 

stockpiled straps were more or less stiff than the controls based on this simple test. Due to the nature of 

the materials used to construct straps, a full study of this type is resource- and time-intensive. 

8 These exercises included 1) normal breathing; deep breathing; breathing while moving their head from side to side; breathing while 

moving their head up and down; reciting the rainbow passage; bending over at the waist and reaching up and down; normal breathing; 

grimace; normal breathing. Grimace FF were not calculated or used for the overall FF. 9 One test subject dropped out before completing the four donnings for Lot C, so a new test subject tested four donnings of the control 

and four donnings for Lot C.
5

Therefore, NIOSH used a simplified test protocol for this current study that was adapted from one of its 

previously published studies on respirator straps [Rottach and Lei 2017]. For each manufacturing lot, the 

average strap extension ratio of the stockpiled straps was then divided by the average strap extension 

ratio for its control straps to arrive at the normalized stockpile strap extension ratio, which was used to 

determine the difference in performance of stockpiled respirator straps.

What NIOSH Found Through Inspection, Testing, and Evaluation

Storage Conditions

• For a full description of Facility Four storage conditions, refer to “Facility Four of Ten: Inhalation and 

Exhalation Resistance and Filtration Efficiency Performance” [Greenawald et al 2020]. Briefly, these 

conditions were: 

o Dust and damage to product packaging was limited or not observed at Facility Four

o Facility lights were off when the facility was not in use

o Small ceiling vents allowed sunlight to enter the facility in specific locations on the top pallets

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

were observed

o Pallets were generally shrink wrapped around the four pallet sides but not across the top or 

bottom

o With the exception of the top-most row, pallets were stacked two-high causing some 

weight/load to be applied to the bottom pallet.

o Some deviation from manufacturer recommended temperature and percent relative humidity 

(%RH) conditions were noted (3M models: 0.02% of the temperature and 0% of the %RH data 

points; KC model: 66.4% of the temperature and 25.8% of %RH data points).

Observations during Donning

• Upon donning the respirators, nine KC 46827 respirators were not used since the straps were broken (in 

the middle of the strap) or broke (from the facepiece and in the middle of the strap) during subject 

donning. Five straps broke from Lot A, and four straps broke from Lot C. Test staff reported that these 

straps felt hardened/stiff to the touch prior to attempting to don. One 3M 1870 strap from Lot A broke 

during donning. These damaged straps affected the sample size of respirators tested, which is further 

explained in Table 2.

Fit Testing Subject Panel 

• The distribution of test subjects for each model sampled from Facility Four as a function of the NIOSH 

panel cell size is shown in Figure 1. For each model, test subjects assigned to panel cells #1, #2, #4, #5, 

#7, and #8 were used. Subjects were sought but could not be identified for cells #3, #6, and #9.
6

Figure 1: Distribution of test subjects by panel and model for Facility Four. Panel cell sizes are shown in blue, 

where the cell sizes used in this study are outlined in red. The model and model size are shown below each 

NIOSH Panel. Differing number of control and stockpile cell sizes were due to 1) test subjects exiting from the 

study and being replaced with new subjects of a different panel cell size; 2) same subject donning the same 

model across multiple lots; 3) as well as straps breaking.
7

Evaluation of Fit Using the Mean Overall FF

• It is important to note that fit testing is inherently variable due to many factors, including inter- and 

intra-subject variabilities [Da Roza et al. 1983; Zhuang et al. 2011, 2015]. Therefore, variability is not 

limited to fit testing aged FFRs, but is observed for new FFRs. 

• In some instances, the mean overall FF for the control respirators was higher, indicating a better fit to 

the user, than the mean overall FF for the stockpiled respirators, and in other instances, stockpiled 

respirators had a higher FF than the controls. Table 2 shows a summary of the fit testing results. 

Differences were assessed through analysis of variance (ANOVA) with post-hoc, Bonferroni adjusted

comparisons. The p-values shown in red indicate a statistically significant difference was identified 

between the control and stockpiled model. Figure 2 shows a summary of the overall FF for each model.

o 3M 1860: No statistically significant differences were detected when comparing the control FF 

(mean [M]= 89.0, SD=66.8) to the mean overall FF when the three stockpiled lot data were 

aggregated (M=101.4, SD=71.5). When comparing each of the three individual stockpiled lots to 

the control, only one stockpiled lot (Lot C, manufactured in 2006) was statistically significantly

different than the control, with a higher mean overall FF (M=112.5, SD=69.4).

o 3M 1870: No statistically significant differences were detected when comparing the mean

control overall FF (M=119.3, SD=70.0) to the average overall FF when the two stockpiled lots 

were aggregated (M=119.8, SD=73.6). When comparing each of the two individual stockpiled 

lots to the control, neither lot was statistically significantly different than the control.

o 3M 8210: The mean control overall FF (M=127.1, SD=74.8) was statistically significantly higher 

than the mean overall stockpiled FF (M=96.3, SD=70.6), p=0.01. This difference was largely 

driven by Lot B. When comparing each of the two individual stockpiled lots to the control, Lot B 

was statistically significantly different than the control, with a lower mean overall FF (M=74.4, 

SD=62.1). Lot A (M=118.2, SD=72.1) was not statistically significantly different. Visual inspections 

of the product packaging or individual respirators did not provide insight on why Lot B had a 

lower FF than Lot A; boxes from both lots were stored outside of the original product cases.

o 3M 9010: No statistically significant differences were detected when comparing the mean

control overall FF (M=97.3, SD=73.3) to the mean overall FF when the two stockpiled lots were 

aggregated (M=106.7, SD=76.0). When comparing each of the two individual stockpiled lots to 

the control, neither Lot A nor Lot B was statistically significantly different than the control.

o KC 46827: A statistically significant difference was detected when comparing the mean control 

overall FF (M=90.6, SD=72.3) to the mean overall FF when the three stockpiled lots were 

aggregated (M=19.0, SD=35.9). All three lots were statistically different than the control, with 

lower overall FF for each of the stockpiled lots.

Evaluation of Pass Rates: Proportion of Donnings and Proportion of Subjects

• Proportion of Donnings Passing (Table 2, Columns 6 – 9)

o Analyses were conducted to determine if there was an overall statistically significant difference 

between the stockpiled and control FFRs in terms of donnings achieving a FF >100 across all 

models. The analyses showed statistical significances that were model specific.

o Subjects donned the respirator four times, where FF varied among the different donnings.

Overall, 248 (49%) of the 503 control donnings achieved a FF>100; 84 (67%) of the control 

respirators had an overall fit factor greater than or equal to 100. In contrast, for the stockpiled 
8

donnings overall, 473 (41%) of the 1,165 donnings achieved a FF>100; 160 (55%) of the 293

respirators achieved a FF>100. When the controls of a specific model were compared to each 

stockpiled lot of the same model through a z-test, the following comparisons were observed:

 3M 1870: no differences between each stockpiled lot and the control

 3M 9010: no differences between each stockpiled lot and the control

 3M 1860 Lot: a statistically significantly higher proportion of Lot C donnings passed 

compared to the control (60% of donnings passed vs. 40% for the control; p<0.004)

 3M 8210 Lot B: a statistically significantly lower proportion of Lot B donnings passed 

compared to the control (26% of donnings passed vs. 65% for the control; p<0.001)

 KC 46827 Lots A, B, and C: a statistically significantly lower proportion of Lots A, B, 

and C donnings passed compared to the control (6%, 5%, and 6% of donnings 

passed the stockpiled lots, respectively, vs. 45% for the control)

• Proportion of Subjects Passing (Table 2, Columns 10 – 13)

o Analyses were conducted to determine if there was an overall statistically significant

difference between the stockpiled and control FFRs in terms of subjects achieving a FF >100

across all models. The analyses showed dependency between the 3M models and the KC 

models and thus the conclusions are model specific.

o For each test subject, if one of any of the four donnings resulted in an overall FF >100, this 

was considered a pass. When the controls of a specific model were compared to each 

stockpiled lot of the same model, the following comparisons were observed:

 3M 1870: no differences between each stockpiled lot and the control.

 3M 9010: no differences between each stockpiled lot and the control.

 3M 1860: a statistically significantly higher proportion of Lot C subjects passed 

compared to the control (81% of the subjects passed vs. 58% for the control; 

p<0.04).

 3M 8210 Lot B: a statistically significant proportion of subjects had lower FFs for Lot 

B when compared to the control (32% of subjects passed the stockpiled lot vs. 76% 

for the control; p<0.002)

 KC 46827 Lots A, B, and C: a statistically significant proportion of subjects fit Lots A, 

B, and C worse than the control (9%, 8%, and 9% of subjects passed the stockpiled 

lots, respectively, vs. 58% for the control).
9

Table 2: Summary of Facility Four Fit Testing Results

Mean FF Donning Proportion Passing Subject Proportion Passing

Model

Control or 

Stockpiled 

Lot

Mean 

FF

Standard 

Error/

Standard 

Deviation

p- values (SP 

Lots 

Compared to 

the Control)

# of 

Donnings

# of 

Donnings 

that 

Passed

(i.e. 

FF>100)

Donning 

Pass 

Rate (%)

p-values

(SP Lots 

Compared 

to the 

Control)

# of 

Subjects

# of 

Subjects 

that 

Passed

Subject 

Pass 

Rate (%)

p-values

(SP Lots 

Compared 

to the 

Control)

3M 

1860

Control 88.96 6.57/66.78 - 103 41 39.8% - 269 15 57.7% -

Lot A

2010 96.11 7.07/70.69 0.75 100 46 46.0% 0.37 25 16 64.0% 0.63

Lot B 2010 95.58 7.38/73.81 0.89 100 42 42.0% 0.75 25 17 68.0% 0.44

Lot C 2006 112.48 6.80/69.36 0.15 100 60 60.0% 0.004 26 21 80.8% 0.04

3M 

1870

Control 119.29 6.99/69.98 - 100 54 54.0% - 25 20 80.0% -

Lot A 120.61 7.38/72.34 0.93 9612 61 63.5% 0.18 2410 19 79.2% 0.94

Lot B 118.94 7.52/75.18 0.91 100 56 56.0% 0.78 25 20 80.0% 1.00

3M 

8210

Control 127.13 7.48/74.77 - 100 65 65.0% - 25 19 76.0% -

Lot A 118.20 7.21/72.10 0.49 100 63 63.0% 0.76 25 18 72.0% 0.76

Lot B 74.44 6.21/62.06 <0.001 100 26 26.0% <0.001 25 8 32.0% 0.002

3M 

9010

Control 97.25 7.45/75.98 - 10410 45 43.3% - 2611 16 61.5% -

Lot A 101.96 7.52/75.24 0.86 100 49 49.0% 0.41 25 17 65.4% 0.77

Lot B 111.42 7.69/76.90 0.50 100 55 55.0% 0.10 25 18 72.0% 0.44

KC 

46827

Control 90.64 7.38/72.28 - 9612 43 44.8% - 2411 14 58.3% -

Lot A 17.97 3.73/34.43 <0.001 8513 5 5.9% <0.001 2212 2 9.1% <0.001

Lot B 18.88 3.06/30.64 <0.001 100 5 5.0% <0.001 25 2 8.0% <0.001

Lot C 20.05 4.55/42.69 <0.001 8414 5 5.7% <0.001 2113 2 9.1% <0.001

9 One test subject dropped out before completing the four donnings for Lot C, so a new test subject tested four donnings of the control 

and four donnings for Lot C.

10 One strap broke, 4 of these 4 donnings could not be completed.

11 One subject dropped out before completing stockpiled Lots A and B, therefore, a new test subject donned the control and Lots A and B. 12 One subject dropped out before completing the four donnings for the control.

13 Four straps broke, 15 of these 16 donnings could not be completed; one complete donning was achieved for one of these respirators 

before the strap broke. 

14 Four straps broke, 16 of these 16 donnings could not be completed.
10

Figure 2: Summary of the Mean Overall Fit Factors for the Control and Stockpiled Respirators Tested. OSHA 29 

CFR 1910.134 States that a FF > 100 is a Pass (Depicted By the Red Dashed Line). Error Bars are Represented as 

the Standard Error of the Mean.

Evaluation of Strap Extension Performance

• Strap Performance

o The average strap extension ratio for each manufacturing lot—normalized by the average strap 

extension ratio of the control straps—is shown in Figure 3. Because the force applied to both 

the stockpiled and control straps was consistent, the lower extension ratio for stockpiled 

respirator straps indicates that they were generally stiffer than their controls. The black line 

represents the strap extension ratios for the controls.

o Differences were assessed through analysis of variance (ANOVA) with post-hoc, Bonferroni 

adjusted comparisons. The asterisks shown in Figure 3 indicate a statistically significant

difference was identified between the control and stockpiled lots.

 3M 1860: all three stockpiled lots were statistically significantly stiffer than the control 

lot.

 3M 1870: no stockpiled lots were statistically significantly different than the control lot.

 3M 8210: stockpiled Lot A was statistically significantly less stiff than the control lot.

There were no visual concerns recorded that could be used to explain the difference 

between the two lots.

 3M 9010: no stockpiled lots were statistically significantly different than the control lot.

 KC 46827: all three stockpiled lots were statistically significantly less stiff than the 

control lot.
11

Figure 3: Average strap extension ratio, normalized by control strap performance shown by stockpiled 

manufacturing lot. Error bars represent the 95% confidence interval and estimate the population parameters. 

The asterisk (*) indicates that the stockpiled lot was found to be statistically significantly different from the 

control respirators of the same product model (p<0.05).

Limitations

This study design limits the generalizability of the results. Limitations include:

• Control samples were not the same lot/manufacturing year as those stockpiled samples.

• Test subject panel cell sizes from cell sizes 1 – 10 were used regardless of respirator model size 

o (e.g., Small, Regular). Subjects were sought but could not be identified for cells #3, #6, and #9.
12

CASE Findings

Findings for the 3M 1860 Model:

Fit Testing: One of three stockpiled lot fit the test subjects better when compared with the control lot.

This model currently has a five-year recommended shelf life; 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 Four and may not be 

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

Strap Testing: The straps from the three stockpiled lots were more stiff than the control lot. 

Findings for the 3M 1870 Model:

Fit Testing: The two stockpiled lots fit the test subjects similarly to the control lot.

One strap broke during donning, possibly due to degradation of the strap material. This model currently has a 

five-year recommended shelf life; Appendix 2 shows two 3M letters to end users with shelf life and 

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

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

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

Strap Testing: No statistically significant differences in strap stiffness were detected between the control lot and 

the stockpiled lots.

Findings for the 3M 8210 Model:

Fit Testing: One of two stockpiled lots did not fit the test subjects as well as the control lot.

No visual inspection concerns were identified. This model currently has a five-year recommended shelf life; 

Appendix 2 shows two 3M letters to end users with shelf life and recommended storage condition information 

[3M 2018, 2020]. Thus, all respirators tested are past their recommended shelf life. These findings pertain to 3M

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

environmental storage conditions.

Strap Testing: Lot A straps were statistically significantly less stiff than the control, whereas Lot B straps were 

not statistically significantly different than the control lot.

Findings for the 3M 9010 Model:

Fit Testing: The two stockpiled lots fit the test subjects similarly to the control lot.

This model currently has a five-year recommended shelf life; Appendix 2 shows two 3M letters to end users with 

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

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

other stockpile facilities and/or under different environmental storage conditions.
13

Strap Testing: No statistically significant differences in strap stiffness were detected between the control lot and 

the stockpiled lots. 

Findings for the KC 46827 Model:

Fit Testing: The three stockpiled lots did not fit the test subjects as well as the control lot.

When fit testing, nine straps broke during donning, possibly due to degradation of the strap material. Five straps 

broke from Lot A, and four straps broke from Lot C. This model currently has a five-year shelf life; Appendix 3

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 Four and may not be applicable to other stockpile facilities and/or under different 

environmental storage conditions.

It’s also important to consider findings from the aforementioned report, where NIOSH evaluated respirators 

from the same KC 46827 lots from Facility Four for breathing resistance and filtration performance [Greenawald 

et al 2020]. Thirty-four individual KC 46827 stockpiled respirators failed out of the 120 tested for filtration 

performance, where 25 of the 34 respirators failed filtration performance from Lot C, and 9 of the 34 respirators 

came from Lot B; both lots were manufactured in 2007. 

Strap testing: The straps for all three stockpiled lots were statistically less stiff than the controls. 
14

The described evaluations showed model-specific changes in fit and strap extension ratios. However, the 

findings cannot conclude whether the change in fit between control and stockpiled respirators was specifically

affected by stockpiling conditions and/or long-term storage. At this time, sufficient information is not available

to definitively know the change in fit of all respirators that 1) are stored for prolonged periods of time; 2) are 

stored under various storage conditions; or 3) have exceeded the approval holder’s designated shelf life. It is 

also not clear why some stockpiled FFRs had better fit than those control FFRs; changes in strap extension 

(elasticity) or manufacturing conditions may be one variable. NIOSH recommends contacting the approval 

holder(s) of the respirators in the stockpile with specific questions regarding the use or disposal of product if it is 

beyond the designated shelf life or questions regarding storage conditions. Users of respirators that have 

exceeded the designated shelf life or were stored outside of designated storage conditions should be 

forewarned to avoid a false sense of confidence; these devices may not provide the same level of fit or filtration 

as those that have not exceeded the designated shelf life or storage conditions. While performing a visual 

inspection of each respirator unit may assist users in identifying possible material degradation, this degradation 

may not always be apparent—a user seal check must be performed with every donning. 

It is not yet known how the strap testing results may impact the protectiveness of respirators. Intuitively, one 

might expect that changes in stiffness could impact respirator fit (e.g., looser straps may contribute to poorer 

fit); however, the magnitude of stiffness change to cause a change in fit is unknown. Previous studies have 

shown that strap length can vary by 10% within the same manufacturing lot [Rottach and Lei 2017]. This 

suggests that a substantial change in stiffness may be needed before fit (and protection) is affected. Thus, no 

assumptions on the effect of fit can be made at this time. However, some trends can be observed. The 

stockpiled straps that generally were less stiff than the controls (e.g., the three KC 46827 lots) had lower overall 

FF than those stockpiled straps that were stiffer than the controls (e.g., the three 3M 1860 lots). However, the 

3M 8210 showed the opposite: Lot B overall FFs were lower than Lot A but had stiffer straps. Overall, storing

respirators beyond the manufacturer-designated shelf life or outside of the recommended storage conditions as 

defined in the user’s instructions can potentially impact the elasticity of the straps. Manufacturers may use this 

information for design considerations or for improved visual inspection procedures.

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

[NIOSH 1997]. However, NIOSH does not assess face seal fit as part of the NIOSH approval of particulate-only 

APRs, including N95 FFRs. Additionally, NIOSH does not have requirements for shelf life or storage conditions for 

particulate-only APRs. The approval holder15 (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 disseminate recommendations related 

to storage and shelf life through resources such as user and web notices. The FFRs tested in this study were 

generally not designed for long-term storage (e.g., over 5 years).

15 An approval may be granted to a non-manufacturing entity.
15

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 products that are beyond their manufacturer specified shelf life. 

• 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 findings 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. 

Acknowledgements

The authors would like to acknowledge former and current NIOSH NPPTL colleagues Dana Rottach, James Harris, 

Robert B. Lawrence, Brenda Boutin, and Christian Coby for their assistance in executing the fit testing study 

design and collecting and/or interpreting the fit testing data.
16

Suggested Citation

NIOSH [2021] PPE CASE: Evaluation of Fit and Strap Extension Performance of Stockpiled Filtering Facepiece Respirators 

from One U.S. Facility. By Greenawald LA, Moore SM, and Yorio PL. 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 P2021-0102. 

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

https://multimedia.3m.com/mws/media/1430383O/3m-filtering-facepiece-shelf-life-letter.pdf. Accessed 09/01/2020.

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 09/01/2020.

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17

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18

Appendix 1 – Strap Testing Protocol

Six-centimeter (cm) sections were marked at the center followed by preconditioning each strap to account for 

strain softening effects. The strap was clamped in a test rig and a force of 2N was applied along the strap length, 

and the length of the marked section was measured. The strap was unclamped, and a final measurement was 

made of the unloaded length. The uniaxial strap extension was calculated from the loaded (i.e., 2N load applied) 

and unloaded lengths, per the formula below:

SSSSSSSSSS EEEE EEEEEEEEEEEE RR = LLLLLLLLLLLL EEEEEE EEEEEE EE−UU UU EEEEEE EEEEEE EE

UU UU EEEEEE
19

Appendix 2 – [3M 2018], [3M 2020]
20
21
22
23
24

Appendix 3 – [Kimberly Clark 2018]