Introduction

FFP1 and FFP2 masks are indispensable protective elements during epidemics. They are intended for single-use, but during a crisis the re-usage is inevitable and disinfection mechanisms are required (1)⁠. During the ongoing SARS-CoV-2 pandemics, hospitals, healthcare centers, and research facilities have implemented different mechanisms of disinfection for these masks, usually involving ultraviolet germicidal irradiation (UVGI) and/or heat of some sort. Nonetheless, these methods are not available to many vulnerable parts of the population, where nonetheless, due to shortage, the re-usage of these masks has become the only option. The need for a viable method of disinfection of face masks is further increased by evidence of SARS-CoV-2 being extremely stable on the surface of surgical masks even after 7 days (2)⁠.

This project intends to create a low budget and portable device that can effectively use UVGI and dry heat to disinfect face masks from SARS-CoV virions and that can be easily reproduced by people who need it.

DIY instruction on making disinfection device

Device set up diagram

●      Temperature must be maintained in the range 65+/-5°C

●      The lamp must provide UV-C wavelength.

●      The disinfection cycle duration is minimum of 30 minutes. (recommendation: Not more than 30 min in order to have a safer range to avoid potential face-mask degradation and loss of functionality.)

Device Dimensions

First Heat testing

Making of the heating system

Important: The frying pan should not touch the wood of the box, as it reduces the heat efficiency. Hence one has to select the right diameter of the hole and shape the metal brackets according to this diagram:

Making of the top cover

For the UV-C source in this device, an 11 W lamp bulb from a “Sterilizer for Aquarium” kit was used. The UV-C bulb was extracted and mounted to the top cover at the two ends of the bulb as shown in the image. The bulb is mounted by creating 4 holes in the top cover and using a zip tie/cable tie and soft padding to securely fasten the bulb. The top surface is covered in aluminium to reflect the UV radiation.

Feel free to use UV-C lamp from other sources. If you do not have access to the crystal tube (used in this project) do not use glass as a replacement as glass blocks the UV radiation.

WARNING:

You must be aware that UV-C radiation is very dangerous for your eyes and skin. The UV-C light must be switched ON only when the top cover of the device is closed and switched off when the device is open.

Due to the unseen danger of UV-C, one must check that the device is light proof. Remember, that the visible radiation of germicide tube is just a by product and it’s only 3/4% of total emission, there’s a big risk of emission leak and one doesn’t perceive it. One has to conduct a light test by checking for light leaks around the device/enclosure in a completely dark environment. One has to cover all the holes/ leaks if found, using some foam gasket and / or some borders to avoid this risk of UV-C leaks outside of the device.

Covering the surfaces with Aluminum foil

Before installing the UV-C tube and the wire rack, cover sides and top surface of the box with aluminum foil, as shown in the image.The goal is to reflect the UV-C light on the side faces, thus augmenting the efficacy.

Tips: Double sided tape can be used to maintain the aluminium foil in place for the surfaces and the edges can be duct tapped.

Making of the Wire rack – Placement for the Face-masks

The face-masks will be placed on top of a wire rack. I wire rack was made using copper thinned wire at 30 mm apart from each wire. The wire rack is 120 mm above the bottom surface. The wire rack is held together by passing the wire through small holes made on the front and back surfaces of the box.

Setting up Arduino & sensors

Temperature and light sensor:

Arduino control

Source code for Arduino

External libraries to include

Adafruit_LEDBackpack.h: https://learn.adafruit.com/adafruit-led-backpack/0-54-alphanumeric-9b21a470-83ad-459c-af02-209d8d82c462

Metro.h: https://github.com/thomasfredericks/Metro-Arduino-Wiring

User Manual

1.     Place the box on top of your induction (or resistive) hob.

2.     Switch the power ON for the Arduino.

3.     Close the box and start to heat at 70~80% of the power of your induction hob.

4.     Wait till you reach the 60°C temperature. Now reduce the change power of induction hob to 30%.

5.     Now you can open the device, place your masks inside and close the device.

6.     Make sure that the UV-C light is plugged.

7.     Push the button to start => the remaining time should be displayed (30 minutes).

8.     From now you just have to wait for the time has decreased to 00 minutes, there will be a signal on the speaker.

9.     To restart at the initial state for a new cycle, just push the button.

Remark: When the timer is counting elapsing time (COUNT state), the small dot between Timer and Temperature displays will blink at 1 second rhythm.

Temperature cycles

Heat inactivation of viruses

The capacity to get rid of microorganisms through moist heat usually under 100°C is known since the time of Pasteur. In this device, we implemented dry heat instead, which is reported to effectively eliminate SARS-CoV infectivity. Assays show considerable inactivation of the virus at 56°C during 30-90 min, almost complete inactivation at 65°C for 20-60 min, and complete inactivation at 75°C during 30-45 min (7,8)⁠. Furthermore, a recent study showed that SARS-CoV-2 lost all detectable infectivity after being incubated at 56°C for 30 min, or 70°C for 5 min (2)⁠.

According to this evidence and additional considerations regarding the effects of these disinfection methods on the functionality of the face masks —which will be explained in the next sections—, we decided to set the heat exposure of the protocol to be used with the device at 65 °C for 30 min.

Germicidal protocols on face masks

So far, we have presented evidence regarding viral disinfection on samples dissimilar to the face masks to which we intend to apply the disinfection. Hence, here we present some reports of viral disinfection on the same type of masks we intend to use.

Disinfection of face masks has been shown to be effective against influenza virus using UVGI at ~1 J/cm2 (10)⁠, UVGI at ~18 J/cm2, or moist heat at 65±5 °C during 3 h (11)⁠. There are no studies of disinfection of masks with coronaviruses, but since influenza viruses are also ssRNA viruses, similar effects could be expected.

Learn more about :

Recommended method for disinfecting face-masks.

It is very important to establish a good procedure for the process of disinfecting used masks. The main questions are about Personalisation, counting the number of disinfection cycles, method of packaging disinfected face-masks. We recommend to take inspiration from this paper “N95 Filtering Facepiece Respirator Ultraviolet Germicidal Irradiation (UVGI) Process for Decontamination and Reuse” published by Nebraska Medicine.

Conclusions

Considering the gathered evidence and technical details of the device, we decided to set the disinfection protocol at 30 min of UVC irradiation and dry heat at 65±5 °C. This time has to be counted considering the time it takes for the device to reach the required temperature and light intensity. Either UVC or heat alone with these specifications should be enough to remove almost all SARS-CoV-2 infectivity, and the simultaneous action of both should increase the effectivity of the method to an even safer level.

Safety considerations

•      You must be aware that UV-C radiation is very dangerous for your eyes and skin. The UV-C light must be switched ON only when the top cover of the device is closed and switched off when the device is open. 

•      Be careful with metallic parts of the box that could be hot after the heating and could burn the skin. 

Disclaimer

Based on the available scientific evidence, the disinfection protocol will likely eliminate almost all SARS-CoV infectivity, and will definitely make the masks much safer to reuse than without any kind of disinfection. However, Needlab and the members working on this project assume no liability for the usage of this device. It was designed with goodwill and to the best of our knowledge and capabilities, but the following must be stated:

No proper laboratory testing has been yet done in terms of SARS-CoV-2 inactivation with this device, nor actual effects on face masks’ filtration capacities can be confidently assessed beforehand. The usage of the device and this guide is a free decision. 

Next Steps

1. Validating the disinfection process with the help of laboratory testing of the disinfected mask.

2. Designing a V2, of the disinfecting device including some optimizations, user feedback and provide the necessary files for making it using methods like laser cutting and CNC.

Team

Jean Noel Lefebvre, Daniel Moreno, Dr Alejandra Duque, Dr Felipe Gutiérrez Arango, Jason Knight, Maria Isabel Velez Isaza, Sameera Chukkapalli.

Bibliography

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2. Chin A, Chu J, Perera M, Hui K, Yen H-L, Chan M, et al. Stability of SARS-CoV-2 in different environmental conditions. medRxiv. 2020 Mar 27;2020.03.15.20036673.

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See also: N95 Decontamination & Reuse Webinar | N95DECON & MGB