[ad_1]
With so many different types of face masks now available in neighborhood stores and heart malls, the question is: How effective are they against Covid-19 and other respiratory infections?
The Sunday Times selected nine types of surgical and reusable masks and put them through two tests.
PARTICLE FILTRATION EFFICIENCY TEST (PFE)
Working with laboratory experts from local testing and inspection company Setsco Services, a Particulate Filtration Efficiency (PFE) test was conducted to measure how well the masks prevent tiny respiratory droplets, 0.1 microns or one millionth subway, escape.
A good mask should have a PFE rate of at least 95 percent.
BREATHABILITY TEST
A breathability test was also conducted to measure how comfortable it is to breathe through the masks.
This author tested the breathability of the six reusable masks, while the breathability of the three surgical masks, which are not reusable, was determined by a differential pressure test.
In the latter group, the masks were subjected to air pressure to determine their resistance. Generally, the lower the resistance, the better the breathability.
A differential pressure reading of less than 40 pascals per square cm indicates that the mask is comfortable for the user.
To determine if masks meet the standards set by ASTM, an international standards organization, a total of five tests must be performed.
They include tests for bacterial filtration efficiency (BFE), fluid resistance and flammability.
The latest DET mask provided by Temasek, which is not among the nine masks tested, has a differential pressure reading equivalent to less than 40 pascals per cm2, but does not have a PFE reading. His BFE, however, is more than 80 percent.
Of the nine masks tested, surgical masks performed well in both tests, while reusable masks reflected a trade-off between breathability and filtration efficiency, the experts said.
Surgical masks had a PFE range of more than 98%, while most reusable masks had a PFE range of 0% to 20%, with the exception of sample four, which had a PFE of 88.51 %.
This means that most reusable masks were not very efficient at filtering 0.1 micron particles, but they can filter larger particles.
Noting the results, Dr. Joel Lee, director of the School of Chemical and Life Sciences at Nanyang Polytechnic, said it is “not surprising” that reusable masks had a lower PFE rate compared to masks. surgical
But he noted that sample four consisted of three layers and had a high-performance filter that kept it dry from external moisture.
It also had a breathable mesh first layer, allowing it to balance breathability with good PFE, he added.
Dr Teo Tee Hui, a board member of the Singapore Institution of Engineers and Senior Lecturer at the Singapore University of Technology and Design, also noted that the mask had such a high PFE because it was made primarily of finely woven nylon.
The other reusable masks that were tested used thick cotton for the inner and outer layers.
“Thick cotton is good for perspiration, but it is porous. Respiratory droplets are not well absorbed, which explains the low filtration efficiency,” he said.
Most reusable masks are double-layered, with either cotton layers or just the inner cotton layer and the outer polyester layer, he added.
Polyester is a good material to use for the outer layer of the mask as it is waterproof and can repel the ingress of droplets. But if the inner layer is made of thick cotton, it could hamper the overall filtration efficiency of the mask.
“Ideally, the best reusable mask should have three layers, with a non-woven fabric as the middle layer to better absorb water particles. That way, the inner and outer layers can be made of porous materials for better breathability, without compromising on filtration efficiency, just like surgical masks, “said Dr. Teo.
Dr. Lee also suggested that the masks be two layers or more and made from a combination of materials, such as gauze or flannel fabric, for better filtration efficiency.
Of the six reusable masks tested by the writer, sample five, a single-layer mask, probably made of polyester or polyurethane (a type of plastic material) or a mix of both materials, was the most comfortable, although its PFE was at zero percent.
Dr. Teo noted that polyurethane, which is frequently used in lingerie, is known for its stretch and comfort, but like polyester, it may not be as effective at catching droplets.
However, it could prevent larger droplets from being released into the environment, although choosing a mask with a better PFE is recommended.
Both experts agreed that a good approach would be to wear surgical masks in high-risk and crowded places, such as hospitals, and to use reusable masks for low-risk activities. Wearing a mask should also be done in conjunction with other measures, such as safe distancing, to ensure people’s safety and hygiene, they added.
Correction note: An earlier version of the article said that Dr. Teo Tee Hui was a board member of the Singapore Institute of Engineers. This has been corrected. We are sorry for the mistake.
[ad_2]
