Dry heat sterilization as a method to recycle N95 respirator masks: The importance of fit

In times of crisis, including the current COVID-19 pandemic, the supply chain of filtering facepiece respirators, such as N95 respirators, are disrupted. To combat shortages of N95 respirators, many institutions were forced to decontaminate and reuse respirators. While several reports have evaluated the impact on filtration as a measurement of preservation of respirator function after decontamination, the equally important fact of maintaining proper fit to the users’ face has been understudied. In the current study, we demonstrate the complete inactivation of SARS-CoV-2 and preservation of fit test performance of N95 respirators following treatment with dry heat. We apply scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) measurements, Raman spectroscopy, and contact angle measurements to analyze filter material changes as a consequence of different decontamination treatments. We further compared the integrity of the respirator after autoclaving versus dry heat treatment via quantitative fit testing and found that autoclaving, but not dry heat, causes the fit of the respirator onto the users face to fail, thereby rendering the decontaminated respirator unusable. Our findings highlight the importance to account for both efficacy of disinfection and mask fit when reprocessing respirators to for clinical redeployment.

Breathing Uneasy: Fit-Tested N95 Respirator Access in Washington State Long-Term Care Facilities

Long-term care facilities (LTCF) have been disproportionately impacted by illness and death from COVID-19. Shortages of respirators for staff, especially Particulate Filtering Facepiece Respirators (N95), have limited LTCFs ability to follow public health recommendations for preventing COVID-19 transmission. Use of N95 respirators was infrequent in Washington State (WA) LTCFs prior to May 2020. N95 respirators must be individually fit tested to provide intended protection; a fit test is a procedure that tests the seal between the N95 respirator and the wearer’s face. The WA Department of Health (WA DOH), collaborated with stakeholders to survey LTCFs in November 2020 regarding needs for fit tested respirators and analyzed responses (n=384). Responses by facility type: 8.3% nursing homes, 17.7% assisted living, 62.8% adult family home, 11.2% other. In WA, adult family homes (AFH) are licensed for six or fewer residents. 23.70% of LTCFs indicated they did not have any N95 respirators in stock at their facility; 96.7% of these were AFH. In August 2020 WA DOH surveyed AFH owners and received 110 responses; 9.76% reported having at least one staff member fit tested for respirators. Smaller facilities may experience increased burden in accessing N95 respirators and fit testing due to lack of established relationships with suppliers and small volumes being purchased. WA DOH used federal COVID funding to contract with mobile fit testing providers and prioritized AFHs for this service. Between December 1, 2020-February 28, 2021, staff at 290 LTCFs were fit tested. The project will continue throughout 2021.

Tractable circula densities from Fourier series

This article proposes an approach, based on infinite Fourier series, to constructing tractable densities for the bivariate circular analogues of copulas recently coined ‘circulas’. As examples of the general approach, we consider circula densities generated by various patterns of nonzero Fourier coefficients. The shape and sparsity of such arrangements are found to play a key role in determining the properties of the resultant models. The special cases of the circula densities we consider all have simple closed-form expressions involving no computationally demanding normalizing constants and display wide-ranging distributional shapes. A highly successful model identification tool and methods for parameter estimation and goodness-of-fit testing are provided for the circula densities themselves and the bivariate circular densities obtained from them using a marginal specification construction. The modelling capabilities of such bivariate circular densities are compared with those of five existing models in a numerical experiment, and their application illustrated in an analysis of wind directions.

A feasible route for the design and manufacture of customised respiratory protection through digital facial capture

The World Health Organisation has called for a 40% increase in personal protective equipment manufacturing worldwide, recognising that frontline workers need effective protection during the COVID-19 pandemic. Current devices suffer from high fit-failure rates leaving significant proportions of users exposed to risk of viral infection. Driven by non-contact, portable, and widely available 3D scanning technologies, a workflow is presented whereby a user’s face is rapidly categorised using relevant facial parameters. Device design is then directed down either a semi-customised or fully-customised route. Semi-customised designs use the extracted eye-to-chin distance to categorise users in to pre-determined size brackets established via a cohort of 200 participants encompassing 87.5% of the cohort. The user’s nasal profile is approximated to a Gaussian curve to further refine the selection in to one of three subsets. Flexible silicone provides the facial interface accommodating minor mismatches between true nasal profile and the approximation, maintaining a good seal in this challenging region. Critically, users with outlying facial parameters are flagged for the fully-customised route whereby the silicone interface is mapped to 3D scan data. These two approaches allow for large scale manufacture of a limited number of design variations, currently nine through the semi-customised approach, whilst ensuring effective device fit. Furthermore, labour-intensive fully-customised designs are targeted as those users who will most greatly benefit. By encompassing both approaches, the presented workflow balances manufacturing scale-up feasibility with the diverse range of users to provide well-fitting devices as widely as possible. Novel flow visualisation on a model face is presented alongside qualitative fit-testing of prototype devices to support the workflow methodology.