Evaluation of Decontaminated N95 Respirators 

Date Tested: 4/23/2020 and 5/12/2020 – 5/14/2020

Respirator Model: 3M 1870 

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

Integrity with Tensile Testing 

Decontamination Method: Gaseous ozone, 450 ppm 

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). 

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

evaluation. 10 respirators were subjected to 5 cycles of the gaseous ozone decontamination process. An 

additional 5 controls were provided. 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 99.93%, 

respectively. All samples 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. 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. Decreases in recorded force were 

found in both the top (0.23%) and bottom (5.31%) straps. 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. 

Other notes: All filters had an unpleasant odor and a couple were visibly dirty. 

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 – 3M 1870, gaseous ozone 450 ppm, 5 cycles

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 1870

gaseous ozone,

5 cycles

Min Fil Eff: 99.72%

Max Fil Eff: 99.93%

1

85 8.9 0.126 0.196 99.80%

2

85 7.8 0.032 0.073 99.93%

3

85 8.0 0.045 0.282 99.72%

4

85 10.3 0.135 0.189 99.81%

5

85 8.2 0.065 0.131 99.87%

Control 1 85 8.2 1.36 1.43 98.57%

Control 2 85 8.6 0.061 0.114 99.87%

Control 3 85 8.8 0.106 0.172 99.83%
Table 2. Manikin Fit Evaluation - 3M 1870, gaseous ozone 450 ppm, 5 cycles

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 1870

gaseous ozone,

5 cycles

Static Advanced 

Medium Headform 

(Hanson Robotics)

6

161 118 137 136

7

200+ 200+ 200+ 200+

8

200+ 200+ 200+ 200+

9

200+ 200+ 200+ 200+

10 200+ 200+ 200+ 200+

Control 4 200+ 200+ 200+ 200+

Control 5 187 121 124 138

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 - 3M 1870, gaseous ozone 450 ppm, 5 cycles

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 1870

gaseous ozone,

5 cycles

1 1.263 1.313

2 1.871 1.790

3 1.978 1.876

Decontaminated Strap 

Average 1.704 1.660

Control 1 1.581 1.758

Control 2 1.865 1.799

Control 3 1.678 1.703

Control Strap Average 1.708 1.753

% Change

((Deconned - Controls) / 

Controls)

-0.23% -5.31%