4. Discussion

4.1 Key findings & Analysis of results

To evaluate the spread of water mist for each mask, we used the method of spraying coloured water mist on the paper marked with points through each mask. The results indicate that the N95 mask consistently had the lowest spread of water mist through it, with an average spread of 0.7cm. On the contrary, the Bandana had the highest spread of water mist through it, with an average spread of 17.0cm. The Bandana had a higher spread of water mist through it than even the control in Test 2. We expected that the 3-ply mask would edge out the 2-ply mask by a little, and the reusable cloth mask with filter's result between the two of them, and the results proved our predictions to be true. The 3-ply mask had a lower spread of water mist, scoring 1.4cm compared to 8.2cm for the 2-ply mask. However, for Test 1 of the reusable cloth mask without filter, there was an anomaly. Compared to Test 2 and 3, there was around a 10cm difference between Test 1 and those tests, which was more than 50%. Therefore, for all the tests with anomalies, we conducted an additional Test 4. 

We have presented the data with a table to allow the general public to refer to this table and easily interpret the data, so they know which mask to use to protect themselves most effectively. Such a method can keep more people safe as it will allow people to make an informed decision when choosing a mask of which to wear to protect themselves and others from the COVID-19 virus. Merits and limitations of the method are also discussed, as well as potential directions for future research are highlighted.

4.2 Explanation of key findings  

The N95 mask has the least spread of water mist, as N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 micron), but all were at least 95% efficient at that size for NaCl particles (Qian, 1998). Hence, with these features, the N95 fared the best. On the contrary, the Bandana had the highest spread of water mist, which is because of the textile breaking up those big particles of the water mist into many little particles, increasing the spread of water mist through it. The 3-ply mask had a lower spread of water mist through it than the 2-ply mask due to the additional filtration layer. We also think that the anomaly in Test 1 of the reusable cloth mask without a filter was due to human error, as we might not have sprayed enough water mist with the spray gun. 

4.3 Evaluation of Hypothesis

Yes. The hypothesis was correct as the N95 had the lowest average spread of water mist at an average spread of 0.7cm. In research conducted by N95 respirators made by different companies were found to have different filtration efficiencies for the most penetrating particle size (0.1 to 0.3 micron), but all were at least 95% efficient at that size for NaCl particles (Qian, 1998). Hence, we can conclude that the N95 mask is the most effective in reducing the spread of water mist.

4.4 Limitations and Areas for improvement 

Firstly, our initial Schlieren setup was also far from perfect, which also forced us to use the paper marked with points set up in the final experiment. At first, we decided to use a cardboard mount to place our mirror, but not only was it unstable, but it was also hard to adjust. In order to get it to stay as still as we could, we had to stabilise it manually using our hands, which further added to its inconsistency. The way we set up the camera and LED was also inconsistent. At first, we tried to mount the camera on cardboard and attach the LED to it using tape. This setup was also very unstable and would not stay still, which caused us not to be able to conduct the experiment as every few seconds, the mirror or LED would go off-alignment, and the camera would then not be able to visualise the Schlieren effect. To solve this problem, we can use adjustable mounts for the mirror and the camera to make the setup more stable.

Secondly, the alternate method of spraying water mist through the mask on the paper marked with points may not have been very reliable, judging from the inconsistent results obtained from the experiment. We may have sprayed different amounts of water each time because we have to pull the spray gun trigger back manually for each test. Alternatively, we could use an automated spray that is consistent in the amount of water it sprays each time.

Lastly, reusing disposable masks may have lowered their effectiveness in reducing the spread of water mist through them. This might have caused subsequent tests to have slight inaccuracies. We can improve this by using a new disposable mask for every test we conduct, thus preventing the slight inaccuracies caused by reusing them.