V1 - 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

Cross sectional diagram of the device.

Remark: Induction hob was used to prove the concept. Dry heat of 65+/- 5 °c can be produced using several other methods. But, induction hob can be used in actual device as well.

Prototype heat testing using tabletop induction hob. The heating element is made of a frying pan (induction compatible) with the handle removed. The diameter is around 22 centimetres.

In 15 minutes required temperature of 70°C is attended. The temperature can be maintained constant by adjusting the power of the induction hob.

Making of the heating system

A frying pan of 22 centimetres diameter (induction compatible) with the handle removed.

Cover the frying pan with aluminum foil for UV-C light reflection.

Make a hole of 20 centimetres at the center of the box/ bottom surface of the device.

In order to maintain the position of the frying pan use four metal holders as shown in the image.

Heating element detail.

When the box is handled "in the air".

When the box is put on the table-top induction hob.

In order to maintain smooth contact with the table top induction hob- use 4 rubber patches at the bottom of the box.

Bottom view- showing the detail of the metal pan.

Making of the top cover

A small lock was used to ensure the closer of the cover.

Two hinges are used in the back to enable smooth movement of the top cover.

UV-C System

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.

In order to turn off the light when the device cover is opened a switch was installed. Diagram representation of the switch.

View of the power switch.

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 taped.

Making of the Wire rack - Placement for the Face-mask

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.

Internal view of the device showing the wire rack.

Back view- showing the detail of the wire rack fixing.

Front view- Wire rack copper thinned wire detail.

Setting up Arduino & sensors

Temperature and light sensor fixed to the interior wall of the box using glue.Arduino Overview

Temperature and light sensor:

Temperature and light sensor fixed to the interior wall of the box using glue.

The wires connected to the temperature and heat sensor as seen in the images are running out of the box to be connected to the Arduino.

Arduino control

INIT: In this state, the LED display indicates the temperature, but you have to wait for it to reach the threshold (70°C) to start the counting of the cycle in state COUNT

COUNT: Minutes elapsed from 30 to 0 are displayed on the LED display, next to the temperature. In the case of temperature is too low, or if the UV light is off, the state will change to ERR.

END: This is the normal state at the end of elapsed time.The speaker will advertise. Push the button to go to INIT again.

ERR: This is the error state, it will be activated if temperature goes too low or if the UV light are off. The speaker will advertise. Push the button to go to INIT again.

Alarms

There are few alarm conditions -If alarm is ON, there is a specific tone sequence on the speaker and messages are displayed on the LED display.

Alarm conditions:

1) If the system is in ERR state (UV light is off/lost or temperature too low)
2) If the temperature is too high (more than 75°C)

Source code for Arduino

Click here for the code

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

This is the temperature curve obtained when starting to heat from ambient temperature (it was near 22°C when the experiment was conducted). When 60°C is reached, change the power of the induction hub to 30%. The threshold of 60°C is reached within 15- 20 minutes

This curve is obtained when the cover of the device is opened and closed to place the masks. This was tested, first time with an opening duration of 1 minute and the second time with opening duration of 30 seconds.
The 70°C threshold is recovered in less than 5 minutes.

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. 

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.

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.

Bibliography

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