As noted, UVGI had strong supporting data for efficacy as a germicidal decontamination process, lower upfront costs, and high throughput volume capacity. As a result, it was employed as a method for FFR decontamination in response to the crisis capacity need due to FFR shortages in the midst of the COVID-19 outbreak. Below, data is reviewed which supplied answers to the questions stated in the introduction. These studies were conducted primarily with the use of H1N1 virus inoculating a variety of different FFRs [2•, 10••, 16].

Radiation dosage

Use of UV radiation for decontamination was extensively tested in the wake of the H1N1 influenza outbreak [2•, 10••, 15, 16, 18]. To assess antiviral efficacy, contaminated coupons of 3M 1870 N95 masks were exposed to variable amounts of UV radiation, as measured in J/cm2. To emulate human use, masks were exposed to soiling agents including synthetic skin oil as well as artificial saliva. One group of coupons was inoculated with virus alone, and another group was inoculated with virus and soiling agents. It was found that viable virus was recovered from samples exposed to 0.5 J/cm2, but after increasing to 1.0 J/cm2 and greater, no viable virus was detected [10••]. In addition, no further discernable log difference in viral recovery was noted as UV exposure increased from 1 to 2 J/cm2 [10••]. Literature review included several studies with interventions using 1.2 J/cm2 to 9.5 j/cm2 finding similar germicidal activity with a log10 reduction average of 3.74 [18].

FFR model

Investigators analyzed whether the irradiation dose could be applied universally to FFRs, or if there would be specific limitations to certain brands. Selected models were 3M 1870, 3M 1960, Kimberly-Clark PFR, Moldex 1512, Precept 65-3395, Gerson 1730, Sperian H-NB095, U.S. Safety AD2N95A, Moldex 1712, U.S. Safety AD4N95, 3M VFlex 1805, Alpha Protech 695, Prestige Ameritech RP 88020, Sperian HC-NB 295F, and Moldex EZ-22 [10••]. These 15 N95 FFR models were inoculated with influenza and exposed to 1 J/cm2 of irradiation. After decontamination doses were administered, the masks were then assayed for remaining viable virus. Tight environmental controls were required to maintain precision of irradiation and to monitor temperature which tends to increase with increasing applied dosage and can have an independent effect on viral viability [10••]. Five of the 15 brands tested exhibited at least a 3 log10 reduction of viable virus. These were the 3M 1870, 3M 1860, Kimberly-Clark PFR, Moldex 1512, and Moldex 1712 [10••]. It was concluded that UVGI can be effective, but it is notably dependent upon environmental factors, as well as the composition of the FFRs. These differences can significantly impact the efficacy of decontamination.

FFR strap integrity

Prior studies have demonstrated that repeated donning and doffing, as well as prolonged FFR use, can have a deleterious effect on fit [8, 9, 10••, 11,12,13,14,15,16,17,18,19,20,21]. It is noted that strap integrity degrades over time resulting in FFR strap failure and breakage in some instances. In addition, there are concerns in regard to the maintenance of an adequate fit after repeated strap stretch. In prior studies, it was noted that there is a dose-dependent relationship between the force required for strap breakage and UVGI dose [16, 18]. Given these concerns, special care was taken with an analysis of fit and strap integrity over repeated use as well as fit after UVGI decontamination. All 15 of the above FFRs were tested with original fit as a control; another group with stretching the straps alone for 10 cycles; and then a third group tested with stretching and UVGI for 10 cycles [10••]. The FFRs were then tested to ascertain reduction of elasticity based upon the amount of necessary force (Newtons, N) to stretch [10••]. The FFRs in each group were then tested for fit by being attached to a breathing simulator with a fit factor of 100 being regarded as a passing score [10••].

In synopsis, a clear correlation was identified between repeated stretches and reduction in the amount of force needed to stretch FFR straps, which was noted at around 6 strap stretches. After this point, there was not significantly reduced mean peak force required to stretch mask straps [10••]. When comparing all FFRs, considering stretches and UVGI decontamination, it was noted that there was a statistically significant change in mean force required for the following models after 10 cycles: 3M 1870, Alpha ProTech 965, Gerson 1730, Kimberly-Clark PFR, and the Moldex 1512 [10••]. In further study, 6 masks were selected to undergo testing for 20 cycles. These were 3M 1860, 3M 1870, 3M VFlex 1805, Kimberly-Clark PFR, Moldex 1512, and U.S. Safety AD4N95 [10••]. Unsurprisingly, a reduction of necessary force for strap stretch was observed with repeated donning and doffing. It was noted that among this group there was no statistical difference between the donning-and-doffing-only group and the UVGI-treated group, suggesting that the repeated donning and doffing are the primary drivers of elasticity reduction and not the decontamination cycle [10••]. Other studies regarding UVGI dose and strap integrity have noted a reduction of strap integrity, with 10–21% reduction in force required to break straps at an approximate dose of 590 J/cm2 and 20–51% reduction at a dose of 2360 J/cm2 [18] Notably, these radiation doses are far higher than those necessary to achieve decontamination.

Using this information, a logical follow-up question would be how many cycles of decontamination and reuse could be performed before a significant drop-off in strap efficacy was observed. Therefore, these same 6 FFRs models were tested with 0 cycles, 10 cycles, and 20 cycles of UVGI [10••]. The 3M 1860, 3M 1870, 3M VFlex 1805, Moldex 1512, and U.S. SafetyAD4N95 all had statistically significant reduction of mean peak force required after both 10 and 20 cycles [10••]. The Kimberly-Clark PFR was the only FFR that was unchanged with mean peak force after both 10 and 20 cycles [10••]. Given this significant degradation of strap mean peak force for most FFRs with repeated cycles of UVGI and/or donning and doffing, a reasonable conclusion would be that reducing reuse to 10 or fewer cycles would limit FFR failures related to strap elasticity reduction.

FFR fit

Regardless of strap integrity associated with UVGI dose, the more clinically apt question would be whether UVGI dose affected FFR fit. In order to test this, a quantitative fit test methodology was employed. After repeated donning and doffing alone, as well as with UVGI decontamination for 10 cycles, fit testing was conducted. All of the tested FFRs maintained a fit factor greater than 100 after 10 cycles [10••]. Six masks were then selected to test for 20 cycles as above, once again including the following masks: 3M 1860, 3M 1870, 3M VFlex 1805, Kimberly-Clark PFR, Moldex 1512, and U.S. Safety AD4N95. Within this group, it was identified that the 3M 1860, 3M 1870, 3M VFlex 1805, and Moldex 1512 maintained fit factor greater than 100 [10••]. These data suggest that the use of UVGI, when used in the context of multiple donning and doffing cycles, does result in some reduction in both strap integrity and fit, but can serve as a viable means for FFR decontamination and reuse if there is proper appreciation for limiting the number of decontamination and don/doff cycles. Healthcare providers should be educated and instructed to discard an FFR if strap elasticity or fit characteristics are in doubt.

FFR filtration and airflow resistance

In addition, airflow resistance (breathability) has been tested to ensure that UVGI decontamination does not impair flow rates through the FFRs. It is accepted that 25 mm H2O is the maximum exhalation resistance for N95 FFRs [18]. In review of untreated, UV-treated, and don/doff for 10 cycles for 15 N95 FFR models, and 20 don/doff cycles for 3M 1860, 3M 1870, 3M VFLEX 1805, Kimberly-Clark PFR, Moldex 1512, and U.S. Safety AD4N95, testing found that there was reduction of resistance for both the Moldex 1512 and Kimberly-Clark PFR. However, reduction of resistance is not necessarily an undesirable effect. The rest of the masks did not demonstrate any statistically significant change in airflow resistance [10••]. Minimal change in FFR resistance has been observed in other studies of N95 FFR decontamination [16, 18]. Additionally, the specific FFR models noted above were then tested after 10 and 20 cycles of UVGI decontamination to determine if particle penetration capacity was maintained. In a similar fashion, none of the FFRs demonstrated any significant change and maintained particle penetrance well below 5%, meeting the intended standard of 95% particle filtration [10••]. A meta-analysis of 6 papers studying FFR UVGI decontamination noted an average particle penetrance of 1.19% following decontamination [18]. In addition, peak flow resistance averaged 9.89 mmH2O with none exceeding 11.44mm H20, all being sufficiently below the desired target of 25 mm H20 [11]. In synopsis, UVGI treatment did not cause a significant reduction in filtration or airflow resistance for tested N95 FFRs.

Decontamination of different respiratory viruses

In anticipation of having to use an UVGI decontamination strategy in the event of a novel pathogen outbreak, the 3M 1870 has been tested with various viruses including Influenza types H1N1, H5N1, and 2 different strains of H7N9 as well as Middle Eastern Respiratory Syndrome coronavirus (MERS) as well as Severe Acute Respiratory Syndrome coronavirus (SARS) [10••]. In addition to the viral challenge, the FFRs were also treated with synthetic saliva and sebum. After UVGI decontamination, all six strains of virus, were undetectable [10••]. These data suggest that UVGI has broad anti-viral activity and is a viable strategy for FFR decontamination and reuse in the event of a respiratory viral outbreak.

Safety of FFRs

In addition to necessary demonstration of effective decontamination without reduction of fit, strap integrity, filtering capacity, or airflow resistance, the following FFRs have been tested to ensure adequate protection against fluid penetration and flammability after 20 cycles of UVGI: 3M 1860, 3M 1870, 3M VFlex 1805, Kimberly-Clark PFR, Moldex 1512, and U.S. Safety AD4N95 [10••]. Of the six models tested for flammability, only the Kimberly-Clark PFR ignited, but flames did not spread after a 1-s exposure [10••]. These FFRs were also tested for fluid penetration with exposure to a high-velocity stream of synthetic blood [10••]. The U.S. FDA allows a failure rate of 4% in such test conditions. Thirty-two FFRs of each brand were tested allowing for 3 failures. Within testing, 3 brands failed once: 3M 1860, Kimberly-Clark PRF, and Moldex 1512 [10••]. However, all of the brands were well within the governing criteria for acceptable performance with fluid exposure [10••].

Synthesis of literature review

The body of literature and extensive work of other investigators, as detailed above, indicates that UVGI at a dose of approximately 1 J/cm2, is effective at reducing contaminant burden by significant log 10 reductions of virus. While in some situations a notable reduction of strap integrity was observed, this did not significantly impair fit factor for these FFRs. Even after multiple cycles of UVGI and reuse, the masks were found to maintain adequate airflow as well as maintaining required particle filtration percentages greater than 95%. UVGI decontamination showed adequate response across a wide range of viruses suggesting that this strategy could be effective for SARS CoV-2.

Acceptance of UVGI by healthcare providers

While UVGI FFR-DR can be feasibly, efficiently, and effectively accomplished, whether or not healthcare providers (HCPs) would accept a decontaminated FFR remained in question. As a result, work involving cognitive tasks analysis interviews, focus groups, and surveys were conducted at the following sites: the University of Nebraska Medical Center, (UNMC), Gulf Coast Regional Medical Center (GCRMC) Stony brook University Hospital (SBUH), and University of Chicago Medical Center (UCMC) [10••].

Notable findings from this inquiry [10••] included the following:

1.

HCPs have strong personal opinions regarding use of FFRs previously worn by others.

2.

HCPs have variable training in the use of PPE.

3.

Compliance with FFR is variable, as many are not fit tested regularly.

4.

HCPs are concerned if decontamination method(s) are translatable to novel viruses.

5.

Practical implications would need thorough planning in order to implement.

6.

HCPs would need means to validate adequate decontamination.

Panels of HCPs indicated their belief that, in the context of a pandemic, no FFR would be most unsafe, extended-use FFR would be moderately safer, and FFR with UV decontamination and reuse would be the safest option given in the survey [10••]. In situations with limited FFR availability, the survey indicated that HCPs would likely be amenable to FFR-DR as compared to no FFR due to limited supplies [10••]. However, one of the greatest concerns for reuse was the notion of sharing FFRs with other HCPs. Many HCPs felt that in spite of decontamination, they would rather reuse their own decontaminated FFR rather than an FFR from another person [10••]. Surveys also demonstrated that staff would need proper training for FFR use [10••]. There are concerns that prior to the COVID-19 pandemic, compliance with FFR recommendations, such as annual fit testing was variable [10••]. To better ensure the success of an N95 FFR decontamination and reuse program, integration of education and process would need to be implemented [10••]. HCPs also felt strongly about the desirability of having the site for FFR decontamination near the point-of-care. This was driven by concerns of cross-contamination while en route to decontamination, time loss for FFR while in transit, and the needed storage space while waiting for decontamination processing.