Modified full-face snorkel masks as reusable personal protective equipment for hospital personnel

Abstract

Here we adapt and evaluate a full-face snorkel mask for use as personal protective equipment (PPE) for health care workers, who lack appropriate alternatives during the COVID-19 crisis in the spring of 2020. The design (referred to as Pneumask) consists of a custom snorkel-specific adapter that couples the snorkel-port of the mask to a rated filter (either a medical-grade ventilator inline filter or an industrial filter). This design has been tested for the sealing capability of the mask, filter performance, CO2 buildup and clinical usability. These tests found the Pneumask capable of forming a seal that exceeds the standards required for half-face respirators or N95 respirators. Filter testing indicates a range of options with varying performance depending on the quality of filter selected, but with typical filter performance exceeding or comparable to the N95 standard. CO2 buildup was found to be roughly equivalent to levels found in half-face elastomeric respirators in literature. Clinical usability tests indicate sufficient visibility and, while speaking is somewhat muffled, this can be addressed via amplification (Bluetooth voice relay to cell phone speakers through an app) in noisy environments. We present guidance on the assembly, usage (donning and doffing) and decontamination protocols. The benefit of the Pneumask as PPE is that it is reusable for longer periods than typical disposable N95 respirators, as the snorkel mask can withstand rigorous decontamination protocols (that are standard to regular elastomeric respirators). With the dire worldwide shortage of PPE for medical personnel, our conclusions on the performance and efficacy of Pneumask as an N95-alternative technology are cautiously optimistic.

Fig 1. Concept of a modified snorkel-mask or "Pneumask" as PPE.

The device consists of a full-face snorkel mask, an adapter, and an FDA or NIOSH-rated filter. b) Air Pathway for the Pneumask. Notation: diodes = valves; ground = atmospheric pressure. c) Original Pneumask adapter from the Prakash Lab was initially designed to be 3D-printed from Carbon RPU-70, a biocompatible resin. Latter versions of the adapter were made and edited by Eric Gagner for injection molding, which allowed for high-tolerance quality parts to be manufactured at high volume. d) A second, option piece designed by Dominic Peralta of Stellar Designs, allows for two quarter-turn NIOSH filters to attach a standard ISO 22mm female port. e) Side view of the Pneumask-G device on an author. f) Industrial filters in the Pneumask-G1 configuration are shown. g) Configurations Pneumask-G and Pneumask-G1 are the main topic of this study. However, we have heard anecdotal reports from the community of people modifying the system to allow for use in "sterile-field" environments, such as by using a surgical mask over the chin valve (S1), taping shut the chin valve (S2), replacement of the chin valve with a second filter (S3), or designing a more complex top adapter part that keeps exhale channels and inhale channels separated; typically also used in conjunction with additional one-way valves. We do not provide recommendations or evaluate the efficacy of Pneumask-S(1–3) designs in this study.

Fig 2. Fit testing.

a) Qualitative fit testing being performed in the Department of Anesthesiology at the University of Utah. b) Qualitative fit testing performed in Prakash Lab at Stanford University. c) modified adapter to use in conjunction with PortaCount devices for quantitative fit testing d-e) Mask with modified adapter and with internal measurement tube routed down through exhale channel. f) Pneumask and PortaCount device basic terminology g) Sampling tube positions can be at the adapter, in the mouth chamber or in the eye chamber. Most conservative tests are done with the sampling tube in the mouth chamber h)Typical operating mode of the PortaCount machine quantitative fit tests. May be used if a HEPA-rated filter is available. i) N95 mode is to be used if a viral filter is used that may have <99% efficiency at peak breathing flow rates. Note that some ventilator inline filters fall into this category. j) Testing completed at Stanford by the occupational health and safety department. k) Testing completed at EPFL by the authors to compare performance to half-face respirators.

Fig 3. Filter efficiency and pressure drop testing.

a) Setup for measuring filter efficiency. b) Setup for measuring pressure drop across filter. c-e) Variety of filters tested, using the setup in a) and b). f) Filter efficiency and pressure drop across filters.

Fig 4. CO2 accumulation testing and CFD simulation.

a) Carbon dioxide washout testing utilizing a headform and simulated lung. b) Visualization of flow velocities within the Decathlon Easy Breath mask in stock configuration. c) Pneumask system with adapter and inline filter added. d) Preliminary CFD results on CO2 species transport, comparing the Pneumask with filter resistance to the stock configuration of the mask.

Fig 5. Exhalation valve performance testing.

a) Exhalation valve on mask. b) Setup for measuring the leak flow of the chin valve of a Decathlon FreeBreath mask, showing the connection to an 8mm tube. c) Connection to an open water tank—system at equilibrium (chin valve opened). The mask is lifted up (chin valve closed) to create a water column of 30mm, which means that a negative pressure of 30mmH2O is applied to the chin valve. d) an example time series curve of water column height in experiments described in c). e) exhalation valve leakage test results of 2 valves from Dolfino Frontier and 5 valves from Decathlon, compared with the NIOSH standard as designated in red square. All valves passed the NIOSH standard. f) Flow rate versus suction pressure before use (dry valve, as per NIOSH standards) and after use. This test was specifically to test if valve performance suffers in the humid environments of user breathing. To the contrary, evidence suggests that moisture tends to improve valve performance, as shown in this data. g) Schematic of a circular chin valve. The force balance determines the time scale of chin valve closure. h) Time-lapse images of the chin valve opening and closing.

Fig 6. Clinical usability of Pneumask.

a)Diagram of Bluetooth amplification solution using only an android cell phone and wireless Bluetooth earbuds placed in the mouth part of the mask (can be placed in a plastic bag to make cleaning easier). b-c) the GUI of our Android app. d) Pneumasks can be used with a disposable plastic hood to offer additional droplet protection. Also shown as references are uses of surgical hood and PAPR [21]. e) Pneumask has been actively used in various healthcare settings.

Fig 7. Global efforts that make Pneumask a rigorously tested solution to PPE shortage.

a)The donation map of Pneumask(in red circle) overlapped with the case number in the US from April of 2020. Map data in Fig 7A and 7B are from the OpenStreetMap foundation (ODbL 1.0 4.3). Fig 7A and 7B are generated and reprinted from Tableau.com software platform under a CC BY license, with permission from Tableau Software LLC, original copyright 2020. b)The donation map of Pneumask globally. It is approved in France, Belgium and Italy, and the approval is under review in UK, Chile and the USA. c) Collaborators wearing Pneumask.