Evaluation of Decontaminated N95 Respirators

Date Tested: 4/14/2020

Respirator Model: N95 3M 1860S

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

Integrity with Tensile Testing

Decontamination Method: Methylene Blue [10 μM] sprayed on face and underside (~7 mL / cycle). Cycle includes 

treatment with 100,000 lux white light for 60 minutes to face side and 30 minutes to underside. 

Decontamination Cycles: 5 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 5 cycles of the Methylene Blue 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-STP0059 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. The strap testing procedure for this evaluation is included in this report because it differs from 

subsequent report. 

Filtration Efficiency Results: The maximum and minimum filter efficiency was 98.65% and 93.59%, respectively. 

Eight of the ten respirators measured more than 95%. Two of the ten respirators measured efficiencies less than 

95%. See Table 1. 

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

evaluated. The manikin fit test procedure used in this assessment did not show any detriments in fit associated 

with the decontamination method used. See Table 2. 

Strap Integrity Results: No visual degradation of the straps was observed. Inconsistent changes were shown 

between the top and bottom straps with the top strap showing a 4.47% decrease in recorded force at 200% 

strain and the bottom strap showing a 4.87% increase in force at 200% strain. While the exact correlation 

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

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

*Controls 1 and 2 were tested for initial penetration only. Control 3 was loaded for 10 minutes.

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 meet the requirements of STP-0059, and 

therefore cannot be considered equivalent to N95 respirators that were tested to STP-0059. 

• BOLD filter efficiencies < 95%.

Treated 

Sample #

Flow Rate

(Lpm)

Initial Filter 

Resistance

(mmH2O)

Initial Percent 

Leakage (%)

Maximum Percent 

Leakage (%) Filter Efficiency (%)

1

Technical difficulties with testing treated sample #1. Data not reportable.

2

85 10.7 1.32 2.02 97.98

3

85 11.4 6.36 6.41 93.59

4

85 10.5 1.75 2.76 97.24

5

85 11.4 2.75 3.28 96.72

6

85 11.7 1.76 2.05 97.95

7

85 11.7 1.02 1.57 98.43

8

85 11.1 1.00 1.35 98.65

9

85 12.0 2.37 3.28 96.72

10 85 12.9 1.76 4.39 95.61

11 85 10.4 5.1 5.90 94.10

Minimum Filter Efficiency: 93.59% Maximum Filter Efficiency: 98.65%

Control 1 85 10.7 0.84 n/a 99.16

Control 2 85 10.1 0.83 n/a 99.17

Control 3* 85 11.2 3.90 4.17 95.83
Table 2. Manikin Fit Evaluation

Static Advanced Medium Headform (Hanson Robotics)

Manikin Fit Factor of Decontaminated N95s

Treated 

Sample #

Result Normal 

Breathing 1

Result Deep 

Breathing

Result Normal 

Breathing 2

Overall 

Laboratory Fit 

Factor

12 200+ 200+ 200+ 200+

13 200+ 147 200+ 179

14 200+ 200+ 200+ 200+

15 200+ 178 200+ 192

Control 4

200+ 200+ 200+ 200+

Control 5

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 200% strain)

Straps from Treated Sample # Force in Top Strap (N) Force in Bottom Strap (N)

1 4.456 4.112

2 4.662 3.766

3 4.487 3.869

Decontaminated Strap Average 4.535 3.916

Control 1 4.666 3.871

Control 2 4.828 3.596

Control Strap Average 4.747 3.734

% Difference

((Controls - Deconned) / Controls) 4.47% -4.87%
Tensile Testing of Elastomeric Straps 

Straps will be removed from 5 respirators as required for particulate filter efficiency testing. These 

straps include the top and bottom straps from 3 respirators that were subjected to the decontamination 

process and additional top and bottom straps from 2 control respirators that are new and have not 

undergone any decontamination process. The integrity of these elastomeric head straps will be 

assessed using an Instron 5943 tensile tester as follows. 

1. Straps will be sectioned into 10-cm segments, with ~15 mm on each side to be clamped.

2. Straps will be inserted into the Instron and pulled at 1 cm/s until 200% strain (30 cm sample

length) is reached.

3. This “pre-stretching” position will be held for 2-15 minutes or until the strap material reaches a

stable state.

4. Straps will be returned to their original position for 45 minutes.

5. Straps will be pulled at 1 cm/s until reaching 150% strain (25 cm length) and held for 45 minutes.

6. The strain will then be reduced until the stress is zero, and the length in this zero-stress state

will be the new sample length.

7. The stress at 200% strain of the new length will be measured and recorded.