Although my research supports the idea that heating face masks up to 60Cº kills all bacteria, the next step was to back this up through experimentation. With the help of Danny (founder of YCI,) I was able to get in touch with Jessie Chung. Jessie Chung is the founder and COO of a local face mask company called FamilyMask. Jessie was kind enough to allow me to make frequent visits to the FamilyMask factory in the Hung Hom/Whampoa area to carry out the experimentation process. I was given access to a device called a luminometer which measures bacteria (in units RLU.) The device looked like a walkie-talkie, with a screen displaying the RLU measurements on the front. On the top right corner, there was a hole where a small container with cotton swab inside it was inserted. The cotton swab was attached to a small capsule that contained liquid. In order to measure bacteria levels, the cotton swab was removed and thoroughly brushed along both sides of the face mask. Next, the cotton swab was put back into its cover, where the capsule with the liquid inside it was squeezed to let the liquid fall onto the swab. From there, the capsule was shaken until the swab was completely soaked in the liquid. Lastly, the container was placed back into the device where it would display the bacteria level on the screen. In order to determine the effectiveness of the solar oven, the bacteria level of the mask was measured before and after the solar disinfection process. In hospitals, they only use face masks with an RLU of 50 or less. However, anything less than 60 is safer for further usage.
In theory, the experimentation process seemed somewhat straightforward. However, we ran into many obstacles while attempting to carry it out. For one, given that the bacteria levels needed to be measured before and after the solar disinfection, it meant that the solar disinfection needed to take place near the factory. Furthermore, the weather conditions played a significant role in this. On multiple occasions, on the days we arranged to meet, it would suddenly start raining which meant that we had to reschedule. In addition to this, there were some days where we would meet in the afternoon, however, the sun was not directly shining on the box which meant that it was not able to reach 60Cº. We concluded that the best time to carry out the experiments would be from 11am-1pm, where the sun would be directly overhead. We also found a local park that was relatively close to the factory that we felt would be best for carrying out the experiments as is was more spacious and private.
Despite these obstacles, we persevered until finally, on August 11, 2021, we completed the first experiment that indicated a decrease in bacteria after the solar sterilization. At 11:53am, the outside temperature was 29Cº. We left the oven out in the sun (with a starting temperature of 28.8Cº.) At 12:04pm, the oven reached 57.2Cº before being left in the oven for 6 minutes. Ideally, the box should have reached 60Cº before starting and it should have been left in the sun for longer. However, the temperature began to gradually decrease after reaching 57.2Cº so we decided to start anyway. At 12:10pm, the temperature of the box was 50.0Cº and we decided to end the experiment as the sun was covered by a cloud. The initial bacteria level of the mask was 41 RLU and after the solar sterilization, it had dropped to 37 RLU. Although it did not decrease by much, given that the masks were only left in the box for 6 minutes and the temperature did not reach the goal of 60Cº, this was still a good sign. Nevertheless, we needed more data before being able to conclude that the oven actually worked. On August 21, 2021, we completed another experiment with 2 masks. The outside temperature was 32Cº and it was a scorching hot day, with barely any clouds covering the sun. At 12:36pm, the box was at 35.1Cº and by 12:49pm, it reached the goal of 60Cº. At this point, I inserted Mask #1 into the box for 10 minutes. By 12:59pm, the temperature of the box had reached 66.4Cº. At 1:01pm, we placed Mask #2 into the box before leaving it for 5 minutes. Coincidentally, the starting and ending temperature of the box during the second experiment was the exact same, starting at 60Cº and ending at 66.4Cº. After returning to the factory, we measured the bacteria levels of both masks again. For Mask #1, the intial bacteria level was 496 RLU. After being left in the solar cooker for 10 minutes, it dropped to 62RLU, which was suitable for further usage. Mask #2 had an initial bacteria level of 193 RLU. After being left in the cooker for 5 minutes, it dropped to 53 RLU, which is also suitable for further usage.
Although the results indicated that the solar cooker was effective in killing bacteria when being left in the solar cooker at 60Cº for 5-10 minutes, more experiments must be completed to support these findings. Nonetheless, from the data collected, it can be inferred that by leaving a face mask in the solar cooker at a temperature above 60Cº for 10 minutes, it can sterilize the mask. Seeing as I have collected limited data, as of now, masks should only be reused one more time (after solar sterilization) assuming that they have been left in the cooker for at least 10 minutes at 60Cº.