Evaluation of Decontaminated N95 Respirators 

Date Tested: 7/15/2020 - 7/16/2020 

Respirator Model(s): 3M 1860 

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

Integrity with Tensile Testing 

Decontamination Method: A standard microwave oven was converted into a N-95 respirator plasma-generating 

decontamination unit by cutting a metal coat hanger to 24.4 cm in length and bending it into a ring with a 2mm gap. This 

antenna is now 2 times the wavelength of the microwaves generated in a microwave oven. This antenna is placed on the 

top of an Inverted coffee cup. 1 ml of saline and 1 ml of 30% hydrogen peroxide are added to the top of the inverted coffee

cup. The masks are suspended in line of sight of the antenna gap, and the microwave oven is turned on at full power for 45 

seconds. 15 seconds into the cycle, an intense plasma is formed at the gap. This creates UV radiation, ozone, OH-radicals, 

O-radicals, oxygen positive and negative ions, and electrons. The plasma stays on for 30 seconds and the respirators are

removed.

Decontamination Cycles: 3 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). 

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

evaluation. This included 7 respirators that were subjected to 3 cycles of the microwave plasma 

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-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: All respirators measured more than 95%. See Table 1. 

Manikin Fit Factor Results: The manikin fit factor showed passing fit factors (greater than 100) for all respirators 

evaluated. See Table 2. 

Strap Integrity Results: No visual degradation of the straps was observed. Decreases in recorded force were 

measured in both the top and bottom straps. See Table 3. 

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.” 
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 1860, 

microwave 

plasma, 3 cycles

Min Fil Eff: 98.81%

Max Fil Eff: 99.50%

1

85 8.3 0.158 0.500 99.50

2

85 8.0 0.477 1.19 98.81

3

85 7.7 0.404 0.910 99.09

4

85 7.8 0.464 0.865 99.14

5

85 8.1 0.256 0.736 99.26

Control 1 85 8.0 0.294 0.788 99.21

Control 2 85 8.1 0.294 0.803 99.20
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 1860, 

microwave 

plasma, 3 cycles

Static Advanced 

Medium 

Headform 

(Hanson Robotics)

6

200+ 200+ 200+ 200+

7

200+ 200+ 200+ 200+

Control 3

200+ 200+ 200+ 200+

Control 4

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 1860, microwave plasma, 3 

cycles

1 2.925 2.814

2 2.894 2.846

3 2.974 2.837

Decontaminated Strap 

Average 2.931 2.832

Control 1 2.839 2.921

Control 2 3.034 3.084

Control Strap Average 2.937 3.003

% Change

((Deconned - Controls) / 

Controls)

-0.2% -5.69%