The importance of fit testing in decontamination of N95 respirators: A cautionary note.

To the Editor: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) COVID-19 pandemic resulted in a critical shortage of personal protective equipment (PPE), particularly N95 filtering facepiece respirators (FFRs). Decontamination methods and reuse of FFRs, including ultraviolet germicidal irradiation (UVGI), hydrogen peroxide vaporization, microwave-generated steaming, and dry heating, have been rushed into implementation. However, if the treatment affects filtration or fit, decontamination is achieved but loss of integrity could be catastrophic to the wearer.

Our recent JAAD publication discusses research with a repurposed dermatology phototherapy desktop device to administer UVGI for N95 decontamination. This letter highlights critical differences in fit testing performance collected for different respirator models treated with UVGI administered with this repurposed unit. The effects on respirators of using the suggested UVGI dose of 1 to 2 J/cm2 were variable.

The respirator fit testing was conducted by the Henry Ford Health System Department of Infection Prevention and Control according to the saccharin solution aerosol protocol laid out by the United States Occupational Safety and Health Administration (OSHA). Irradiation of respirators with UVGI was conducted by the Henry Ford Health System Department of Dermatology Photomedicine Unit. A new, unused respirator served as the test respirator, and irradiation was performed after establishing that an unused respirator passed a baseline fit test. The outside-facing and wearer-facing surfaces of the respirators were irradiated by the Daavlin Desktop UVC Germicidal Lamp (Daavlin, Bryan, OH) with a dose of 1.5 J/cm2 to each side. If the respirator passed this test, it was considered to have successfully completed 1 cycle. This process was then repeated to establish the number of irradiation cycles that the respirator would pass the fit test. Testing was ceased if a respirator did not pass the fit test. The results are reported in Table I .

Table I

Results of Henry Ford Health System respirator fit testing

FFR model∗	Saccharin solution aerosol fit test performed	UVC cycles attempted/fit test cycles passed	Passing cumulative UVC dose (3 J/cm2 = 1 cycle)
3M N95 Respirator—1860 NIOSH TC-84A-0006	Baseline, cycles 1-6, 15, 20 & 25	25/20	60 J/cm2
3M N95 Respirator—9210 NIOSH TC-84A-2669	Baseline, cycles 1-2	2/2†	6 J/cm2
3M N95 Respirator—8210 NIOSH TC-84A-0007	Baseline, cycles 1-2	2/1	3 J/cm2
Cardinal Health USA N95 R/S Respirator—NIOSH TC-84A-5529 & 5527 (small/regular)	Baseline, cycles 1-2	2/1	3 J/cm2
Moldex N95 Respirator #2300N95—NIOSH TC-84A-0328	This N95 respirator passed the baseline fit test on 1 individual. Owing to immediate breakage of straps upon user removal on 2 respirators, testing ceased.	0	N/A
Moldex N95 Respirator 1511 (small)—NIOSH TC-84A-0013	This N95 respirator failed the baseline fit test on 3 individuals.	0	N/A
Moldex N95 Respirator 1512 (medium)—NIOSH TC-84A-0013	Baseline, cycles 1-3	3/2	6 J/cm2
3M N95 Respirator—9010 NIOSH TC-84A-4243	This N95 respirator failed the baseline fit test on 2 individuals.	0	N/A
Cardinal Health USA N95A-S Respirator—NIOSH TC-84A-5463	This N95 respirator failed the baseline fit test on 2 individuals.	0	N/A
GB2626-2206 KN95 Respirator—KN95-01-01	This N95 respirator failed the baseline fit test on 2 individuals.	0	N/A

FFR, Filtering facepiece respirator; N/A, not available; NIOSH, National Institute for Occupational Safety and Health; UVC, ultraviolet C.

3M, St Paul, Minnesota; Cardinal Health, Dublin, Ohio; Moldex-Metric, Culver City, California.

Limited resources prevented testing of additional UVC cycles.

The UVGI treatment may degrade polymers in the respirators themselves and impact the elasticity of the bands. The myriad respirators available in this crisis react differently to a given UVGI dose and survive different numbers of decontamination cycles. This may hold true for other respirator treatment methods as well.

Our data strongly indicate that to protect the safety of the N95 respirator user, fit testing after decontamination must be done each time a new model is introduced to a health care system. This has significant safety implications, because varied decontamination methods are being used by different institutions. In addition, N95 respirators should be physically examined before and after decontamination cycles to check for signs of degradation that may have occurred while removing and handling.