Evaluation of Decontaminated N95 Respirators 

Date Tested: 9/22/2020 

Respirator Model(s): 3M 8200 

Tests: Filtration with NaCl (modified version of STP-0059) and Strap Integrity with Tensile Testing 

Decontamination Method: Chlorine Dioxide; Each N95 FFR was sealed in its own Tyvek envelope and placed in its own 2 L 

glass jar with 1/3 of a paper towel and a 10 mL glass beaker. 100 μL saturated aqueous solution of technical grade sodium 

chlorite (80% by mass NaClO2, 18% NaCl) and 100 μL saturated aqueous sodium hydrogen sulfate were added as separate 

drops to the bottom of the 10 mL beaker. The jar was sealed with a metal screw-on lid with Luer lock feedthrus and stop 

cocks. The jar was tipped to mix solutions and begin chlorine dioxide generation. After 120 minutes, 10 mL saturated 

aqueous sodium sulfite was added by syringe needle through a feedthru to wet the paper towel. After another 120 

minutes, the FFR was removed from the Tyvek envelope. This process was repeated for a total of 4 cycles for each FFR. The 

total dose of chlorine dioxide to each FFR was approximately 4 x 2,500 ppm-hours, as measured by gas sampling through 

the feedthrus and measurement of the optical absorbance at 351 nm. 

Decontamination Cycles: 4 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). 

Eight respirators that were unworn and not subjected to any pathogenic microorganisms were submitted for 

evaluation. This included 4 respirators that were subjected to 4 cycles of the chlorine dioxide decontamination 

process and an additional 4 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-APRSTP-0059 to determine particulate filtration efficiency. The TSI, Inc. model 8130 using sodium chloride aerosol 

was used for the filtration 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: All respirators (4 control and 4 decontaminated) measured greater than 95%. See 

Table 1. 

Strap Integrity Results: Visual degradation of the straps was observed during testing, with small pieces of the 

elastomer straps flaking off as stretching occurred. Both the top (-11.55%) and bottom (-7.09%) straps showed 

decreases in recorded force. See Table 2. 

Other notes: The nosepiece foam on the 3M 8200 decontaminated samples were discolored (yellow/brown 

color, whereas control was grey). The straps on the 3M 8200 decontaminated samples were also discolored 

(yellow/brown color, whereas control was white). 
Figure 1. Laboratory Test Photos

Fig. 1A TSI 8130 Filter Tester Fig. 1B Instron 5943 Tensile Tester

A B
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 8200, Control 

Control 1 85 11.4 0.609 0.609 99.39

Control 2 85 10.9 0.495 0.556 99.44

Control 3 85 10.4 1.11 1.17 98.83

Control 4 85 11.8 0.661 0.661 99.34

3M 8200, Chlorine 

Dioxide, 4 cycles

Min Fil Eff: 99.39%

Max Fil Eff: 99.59%

1 85 12.2 0.601 0.610 99.39

2 85 11.7 0.537 0.543 99.46

3 85 11.6 0.554 0.567 99.43

4 85 11.6 0.402 0.414 99.59
Table 2. 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 8200, Control 

Control 1 3.730 3.525

Control 2 3.734 3.556

Control 3 3.716 3.640

Control 4 3.747 3.432

Control Strap Average 3.732 3.538

3M 8200, Chlorine Dioxide, 4 

cycles 

1 3.324 3.242

2 3.414 3.257

3 3.253 3.391

4 3.211 3.256

Decontaminated Strap 

Average 3.301 3.287

% Change

((Deconned – Controls)/ 

Controls)

-11.55% -7.09%