Reusability of P3 facial filter in pandemic emergency: a 3D Analysis of a filter microstructure with X-Ray micro-tomography images after dry heat and UV sterilization procedures.

Abstract

Objective: We sought to evaluate the effects of heating and UltraViolet (UV) sterilization on level 3 protection microstructure (P3) used on disposable filtering facepieces.Intervention: P3 facial filter has been exposed to dry heat and UV sterilization procedures.Methods: P3 facial filter samples underwent standardized sterilisation processes based on dry heat and UV irradiation techniques. We analysed key parameters of internal microstructure, such as fibres thickness and porosity, before and after sterilization using 3D data obtained with a synchrotron radiation based X-ray computed microtomography (Micro-CT). The analyzed filter has two inner layers that we called "finer" and "coarser" layers. The "finer" layer consists of a dense fibers network while the "coarser" layer has a less compact fiber network. Results: Analysis on 3D images showed no statistically significant differences between P3 Filter of Controls and dry heat/UV sterilized samples. In particular, averages fibres thickness in the finer layer of Controls, 60° dry heated and UV irradiated samples group was almost identical for each group. Average fibres thickness for coarser layer of Controls, 60° dry heated and UV irradiated samples group was very similar measuring 19.33 µm (±0.47), 18.33 µm (±0.47) and 18.66 µm (±0.47), respectively. Of note, there was no substantial difference in fibres maximum thickness in the finer layers and coarser layers. For Controls group samples maximum thickness was on average of 11.43 µm (±1.24) in the finer layer and 59.33 µm (±6.79) in the coarser layer. Similarly, 60° dry heated group samples were thickened 12.2 µm (±0.21) in the finer layer and 57.33 µm (±1.24) in the coarser layer, while UV irradiated samples group the mean max thickness is 12.23 µm (±0.90) in the finer layer and 58.00 µm (±6.68) in the coarser layer.Theoretical porosity analysis resulted of 74% and 88%, for finer and coarser layer, respectively. Theoretical porosity of finer layers tend to decrease on dry heat and UV irradiated samples when compared with the respective controls samples.Conclusions: Dry heat and UV sterilization processes do not substantially alter morphometry of the internal microstructure of the P3 filter samples studied with Micro-CT. The current study suggests that safe P3 filter facepiece reusability is theoretically feasible and should be further investigated.

Ultraviolet-C as a Viable Reprocessing Method for Disposable Masks and Filtering Facepiece Respirators

“…Ultraviolet-C is normally regarded as a low-cost reprocessing method. From the SLR’s final sample, most publications used either adapted biosafety [ 6 , 49 , 50 , 57 , 58 , 59 , 61 , 83 ] or sterilization [ 33 , 56 , 86 ] cabinets; adapted chambers [ 7 , 39 , 43 , 48 , 64 , 66 , 75 , 78 ], rooms [ 51 , 68 , 69 , 85 ] or laminar flow cabinets [ 43 , 71 , 80 , 82 ]; the lamps alone [ 38 , 40 , 46 , 52 , 54 , 63 , 79 , 87 ] or tube racks [ 70 ]. Most of these resources are available in research departments or hospitals; making this method “reasonably (…) inexpensive” [ 7 ] (p. 515) or, at least, “a cost-effective alternative to heat or chemical decontamination” [ 69 ] (pp.…”

“…In the matter of effortlessness application of UVGI, fewer studies [ 7 , 34 , 41 , 44 , 48 , 55 , 72 , 73 , 87 ] discuss it. Usually, this characteristic relates to how easy the insertion of these setups into the potential users’ facilities is or how workers benefit from it amidst each patient consultation.…”

“…There are three common problems the UV-C sterilization process demonstrates: the possibility of thermal deformation, shadowing, and absorption effects [ 4 , 5 , 8 , 27 , 31 ]. As the first potential problem (changes in integrity) already discards reprocessed SUPPE, we opted to leave it on Table 1 column “Changes in integrity or fit.” From our SLR database, 30 studies (51.72%) assess it, of which 21 [ 33 , 35 , 37 , 40 , 44 , 48 , 49 , 51 , 53 , 61 , 62 , 64 , 65 , 67 , 70 , 71 , 73 , 80 , 81 , 82 , 87 ] observe no physical changes within different rounds of sterilization or extenuating conditions. On the other hand, nine studies [ 36 , 38 , 42 , 47 , 54 , 75 , 78 , 84 , 86 ] find that masks or FFRs degraded, or faced changes in airflow resistance [ 36 , 47 , 75 , 78 ], or reached minimum acceptability levels after some rounds of reprocessing [ 38 , 42 , 54 , 84 , 86 ].…”

“…Another potential problem reprocessed masks and FFRs might present the reduction of their filtration power. Most studies [ 35 , 36 , 38 , 39 , 42 , 43 , 44 , 48 , 49 , 51 , 54 , 59 , 61 , 62 , 64 , 67 , 73 , 76 , 80 , 81 , 82 , 84 , 87 ] indicate that little or no effect happened as these SUPPE faced UV-C sterilization. However, this is not a consensus in the SLR’s final sample.…”