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Evaluation of Decontaminated N95 Respirators 

Date Tested: 2/11/2021 – 2/18/2021 

Respirator Model(s): 3M VFlex 1804

Tests: Filtration with NaCl (modified version of STP-0059), Manikin Fit Factor with Static Advanced Headform, and Strap 

Integrity with Tensile Testing 

Decontamination Method: Dry heat decontamination was performed in a 2 ft3 environmental chamber. Each respirator 

was sealed in its own Tyvek sterilization pouch and loaded into the chamber. All respirators were exposed to cycles of 75-

78°C recirculating hot air for 45 minutes, followed by cooling to ambient. 10 consecutive cycles of heat treatment were 

performed. Chemical indicators were affixed to the pouches to verify that the respirators reached the target 

decontamination temperature. Temperature profiles were also recorded to confirm that the air temperature in the 

chamber remained within specification for the entirety of the soak segment during each cycle. 

Decontamination Cycles: 10 cycles 

While decontamination and reuse of FFRs are not consistent with standard and approved usage, these options may need to 

be considered when FFR shortages exist. This assessment was developed to quantify the filtration efficiency and manikin fit 

factor1 of an N95 respirator that has been decontaminated. This assessment is not to determine the effectiveness of the 

decontamination procedure at killing pathogenic microorganisms. The results provided in this report are specific to the 

subset of samples that were provided to NPPTL for evaluation. These results may be used to update the CDC guidance for 

Crisis Capacity Strategies (during known shortages). 

Twenty respirators that were unworn and not subjected to any pathogenic microorganisms were submitted for evaluation. 

This included 15 respirators that were subjected to 10 cycles of the Dry Heat decontamination process and an additional 5 

respirators that served as controls. Figure 1 photos document the procedures used. The samples were tested using a 

modified version of the NIOSH Standard Test Procedure (STP) TEB-APR-STP-0059 to determine particulate filtration 

efficiency. The TSI, Inc. model 8130 using sodium chloride aerosol was used for the filtration evaluation. For the laboratory 

fit evaluation, a static manikin headform was used to quantify changes in manikin fit factor. The TSI, Inc. PortaCount® PRO+ 

8038 in “N95 Enabled” mode was used for this evaluation. Additionally, tensile strength testing of the straps was performed 

to determine changes in strap integrity. The Instron® 5943 Tensile Tester was used for this evaluation. The full assessment 

plan can be found here. 

Filtration Efficiency Results: The minimum and maximum filter efficiencies were 99.72% and 99.91%, respectively. All

respirators measured efficiencies greater than 95%. See Table 1.

Manikin Fit Factor Results: The manikin fit factor showed passing fit factors (≥ 100) for all respirators evaluated. 

See Table 2. 

Strap Integrity Results: The top straps showed a 6.47% decrease in recorded force and the bottom straps showed a 9.17% 

decrease in force. See Table 3. 

Other Notes: The 3M VFlex 1804 treated respirators had observable blurring of the printed information found on the 

respirators. Figure 1A-1B shows a comparison between a control sample and a treated sample. 

1The American Industrial Hygiene Association defines the Manikin Fit Factor as “An expression related to the amount of leakage measured through the 

face or neck seal of a respirator mounted to a manikin under specified airflow and environmental conditions. If the challenge to the seal is an airborne 

substance, it is the ratio of its airborne concentration outside the respirator divided by the concentration that enters the respirator through the seal. If the 

challenge is airflow or air pressure, conditions and assumptions for quantifying leakage must be specified. Leakage from other sources (e.g., air purifying 

elements) must be essentially zero. The respirator may be mounted to the manikin without sealants; be partially sealed to the manikin; or be sealed to the 

manikin with artificially induced leaks.” 
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Figure 1. Sample Observations 

Fig. 1A. 3M VFlex 1804 - Control 

Fig. 1B. 3M VFlex 1804 - Sample

A

B
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Figure 2. Laboratory Test Photos

Fig. 2A. TSI 8130 Filter Tester Fig. 2B. Medium Static Advanced Headform Fig. 2C. Instron 5943 Tensile Tester

A B C
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Table 1. Filter Efficiency Evaluation

Notes:

• The test method utilized in this assessment is not the NIOSH standard test procedure that is used for certification 

of respirators. Respirators assessed to this modified test plan do not necessarily meet the requirements of STP0059, and therefore cannot be considered equivalent to N95 respirators that were tested to STP-0059. 

Respirator Model, 

Decon Method, # 

of cycles

Treated 

Sample #

Flow Rate

(Lpm)

Initial Filter 

Resistance

(mmH2O)

Initial Percent 

Leakage (%)

Maximum 

Percent 

Leakage (%)

Filter 

Efficiency 

(%)

3M VFlex 1804, 

Controls 

Control 1 85 4.9 1.590 1.720 98.28

Control 2 85 4.8 0.134 0.159 99.84

Control 3 85 4.7 0.428 0.463 99.54

3M VFlex 1804, 

Dry Heat, 10 cycles

Min Fil Eff: 99.72%

Max Fil Eff: 99.91%

1 85 4.6 0.073 0.104 99.90

2 85 4.7 0.055 0.114 99.89

3 85 4.5 0.046 0.093 99.91

4 85 4.2 0.064 0.097 99.90

5 85 4.2 0.281 0.285 99.72

6 85 5.1 0.105 0.119 99.88

7 85 4.7 0.083 0.128 99.87

8 85 4.6 0.136 0.168 99.83

9 85 4.2 0.145 0.175 99.83

10 85 4.6 0.097 0.135 99.87
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Table 2. Manikin Fit Evaluation

Manikin Fit Factor of Decontaminated N95s

Respirator Model, 

Decon Method, # of 

cycles

Treated

Sample #

mFF Normal 

Breathing 1

mFF Deep 

Breathing

mFF Normal 

Breathing 2

Overall 

Manikin Fit 

Factor

3M VFlex 1804, 

Controls 

Static Advanced 

Medium Headform 

(Hanson Robotics)

Control 4 200+ 200+ 200+ 200+

Control 5 200+ 200+ 200+ 200+

3M VFlex 1804, Dry 

Heat, 10 cycles 

Static Advanced 

Medium Headform 

(Hanson Robotics)

11 200+ 200+ 200+ 200+

12 200+ 200+ 200+ 200+

13 200+ 200+ 200+ 200+

14 200+ 200+ 200+ 200+

15 200+ 200+ 200+ 200+

Notes:

• Per OSHA 1910.134(f)(7), if the fit factor as determined through an OSHA-accepted quantitative fit testing protocol 

is equal to or greater than 100 for tight-fitting half facepieces, then the fit test has been passed for that respirator.

• This assessment does not include fit testing of people and only uses two exercises (normal and deep breathing) on 

a manikin headform. 

• This assessment is a laboratory evaluation using a manikin headform and varies greatly from the OSHA individual 

fit test. This headform testing only includes normal breathing and deep breathing on a stationary (non-moving) 

headform; therefore, fit results from this assessment cannot be directly translated to using the standard OSHAaccepted test. Instead, this testing provides an indication of the change in fit performance (if any) associated with 

the decontamination of respirators. 

Table 3. Strap Integrity Evaluation

Tensile Force in Respirator Straps of Decontaminated N95s

(recorded force values are at 150% strain)

Respirator Model, Decon 

Method, # of cycles Straps from Treated Sample # Force in Top Strap (N)

Force in Bottom 

Strap (N)

3M VFlex 1804, Controls 

Control 1 2.830 2.991

Control 2 2.775 2.825

Control 3 2.726 2.893

Control Strap Average 2.777 2.903

3M VFlex 1804, Dry Heat, 10 

cycles 

1 2.597 2.741

2 2.700 2.637

3 2.338 2.484

4 2.754 2.685

Decontaminated Strap 

Average 2.597 2.637

% Change 

((Deconned – Controls)/ 

Controls)

-6.47% -9.17%