Evaluation of Decontaminated N95 Respirators 

Date Tested: 5/8/2020-5/11/2020 and 5/15/2020 – 5/18/2020 

Respirator Model: 3M 8000 

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

Integrity with Tensile Testing 

Decontamination Method: Treatment with gas phase chlorine dioxide at 1000~2000 ppm·hr

Decontamination Cycles: 5, 10, and 20 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). 

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

evaluation. This included 15 respirators that were subjected to 20 cycles of the chlorine dioxide gas 

decontamination process, 15 respirators subjected to 10 cycles, 15 respirators subjected to 5 cycles, and an 

additional 15 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 98.84% and 99.30%, 

respectively for the 3M 8000 (20 cycles). All respirators measured more than 95%. See Table 1. Filter efficiencies 

for the 3M 8000 (5 and 10 cycles) were not assessed. 

Manikin Fit Factor Results: One control respirator did not achieve acceptable fit (mFF ≥ 100). However, since all 

other control respirators achieved acceptable fit, the treated samples were assessed for manikin fit. All samples 

treated at 5 cycles and 10 cycles achieved acceptable fit, while one sample at 20 cycles did not. See Table 2. 

Strap Integrity Results: The 3M 8000 decontaminated straps (5, 10, and 20 cycles) were discolored 

(brownish), compared to the control straps (white). Top and bottom straps showed decreases in recorded force 

at 5 cycles (10.24% and 6.14%), 10 cycles (15.03% and 6.14%), and 20 cycles (7.87% and 4.73%). While the exact 

correlation between the force exerted by straps and fit is not well understood, higher force values may be 

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.” 
associated with a tighter fit of the respirator to the face. Significant reductions in this force would be associated 

with a loss of elasticity of the straps, thereby reducing their ability to create a tight fit. See Table 3.

Figure 1. Laboratory Test Photos
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 8000, Chlorine 

Dioxide, 20 cycles

Min Fil Eff: 98.84%

Max Fil Eff: 99.30%

1

85 12.6 0.399 0.706 99.29

2

85 12.0 0.437 0.704 99.30

3

85 11.3 0.730 1.160 98.84

4

85 11.5 0.534 0.898 99.10

5

85 11.8 0.407 0.778 99.22

6

85 11.3 0.512 0.891 99.11

7

85 11.8 0.497 0.862 99.14

8

85 12.1 0.421 0.837 99.16

9

85 12.4 0.381 0.797 99.20

10 85 12.0 0.526 0.920 99.08

Control 1 85 12.2 0.354 0.583 99.42

Control 2 85 11.8 0.446 0.761 99.24

Control 3 85 11.6 0.368 0.624 99.38
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 8000, Chlorine 

Dioxide, 0 cycles

(control)

Static Advanced 

Large Headform 

(Lunar Studios)

Control 4 70 57 62 62

Control 5 186 94 82 106

Control 10 200+ 200+ 200+ 200+

Control 11 200+ 200+ 200+ 200+

Control 12 200+ 200+ 200+ 200+

Control 13 200+ 200+ 200+ 200+

3M 8000, Chlorine 

Dioxide, 5 cycles

Static Advanced 

Large Headform 

(Lunar Studios)

11 153 107 73 101

12 200+ 200+ 200+ 200+

13 200+ 200+ 200+ 200+

14 200+ 200+ 200+ 200+

15 200+ 200+ 200+ 200+

3M 8000, Chlorine 

Dioxide, 10 cycles

Static Advanced 

Large Headform 

(Lunar Studios)

11 200+ 200+ 200+ 200+

12 200+ 200+ 200+ 200+

13 200+ 170 169 179

14 200+ 200+ 200+ 200+

15 139 112 73 100

3M 8000, Chlorine 

Dioxide, 20 cycles

Static Advanced 

Large Headform 

(Lunar Studios)

11 167 129 115 134

12 104 93 81 92

13 200+ 200+ 200+ 200+

14 200+ 191 159 182

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. 

• BOLD overall manikin fit factor < 100.
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 8000, Chlorine Dioxide,

0 cycles (control)

Control 1 4.003 3.544

Control 2 4.006 3.669

Control 6 4.052 3.566

Control 7 3.861 3.578

Control 8 3.848 3.433

Control 9 3.782 3.515

Control Strap Average 3.925 3.551

3M 8000, Chlorine Dioxide,

5 cycles

1 3.459 3.308

2 3.560 3.361

3 3.549 3.330

Decontaminated Strap Average 3.523 3.333

% Change

((Deconned - Controls) / Controls) -10.24% -6.14%

3M 8000, Chlorine Dioxide, 

10 cycles

1 3.499 3.231

2 3.249 3.357

3 3.256 3.410

Decontaminated Strap Average 3.335 3.333

% Change

((Deconned - Controls) / Controls) -15.03% -6.14%

3M 8000, Chlorine Dioxide, 

20 cycles

1 3.535 3.487

2 3.614 3.324

3 3.700 3.339

Decontaminated Strap Average 3.616 3.383

% Change

((Deconned - Controls) / Controls) -7.87% -4.73%