EnglishViews: 471 Author: Grand Packing Publish Time: 2020-04-24 Origin: Grand Packing
Why should we wear mask? COVID-19 spreads among human beings, especially when we contact secretions of the infected. The virus contagion determines their spreading manners. COVID-19 can be spread through the body fluid of sniff or cough. If we touch something once touched by the infected and then touch our mouths, noses and eyes with our hands, virus might also be spread.
Generally speaking, there is about 1L liquid in our lungs. Every sniff will make the lungs to be extruded and jet the liquid out in mist. Outside our bodies, the liquid can be atomized into over 40,000 droplets. Every droplet also contains a large number of viruses and bacteria. Because of powerful thrust from our bodies, the liquid can be spread in a high speed of 35m/s and the spreading distance can be 3-8 meters. In this case, wearing face masks can effectively prevent us from virus spreading.
When we observe masks, we can find that general masks all have three layers and some have even four or five layers. For three-layer masks, the outermost layer is non-woven to prevent dust. The middle layer is made of melt-blown non-woven and processed by high voltage of 10,000V. Fine piles are formed to generate static electricity and absorb particles. The innermost layer is skin-friendly non-woven.
N95 can filter more than 95% particles in air. And COVID-19 can be spread by droplets so that it can be prevented effectively by N95 respirator.
Currently, masks on the market are of many kinds, including industrial mask, medical mask, children’s mask... However, only masks whose grade is higher than N90 can prevent virus effectively. That is, if N95 is not available on the market, N90 can be an alternative.
If we are in epidemic area, it’s better for us to wear medical N95 respirator, which cannot only prevent droplets, but also be antibacterial. Besides, cup-shaped masks are better than unsealed masks.
On the other hand, if we are not in epidemic area, medical masks are not needed. We can use N90 or better industrial masks.
Actually, some masks of 3M, Honeywell or some foreign brands that are sold in China are mostly produced by their foundries in China. This indicates that Chinese production technologies are trustworthy.
Except production site, we also concern brands. However, in testing lab of producing factories, masks of every batch will be sampled and these samples tested on an expensive tester. The machine can simulate human breathing, jet particles to masks and then test penetrated particles with photometer. These tested domestic masks’ filtering efficiency is 99.512, high than the figure of N95 standard.
In addition, anti-aging of these mask will be tested. The masks are tested in an aging tester to simulate and test if they can keep utility after 3-5 years. Only those masks of qualified attenuation can be out of factory.
Industrial mask can be used for three days without epidemic. However, based on current situation, experts suggest us to change face mask every four hours. Generally, if we need to be out for a long time, 2 masks are enough.
However, why cannot we use masks repeatedly? That’s because the melt-blown material of mask, once wetted by exhaled air, will lose its function of static absorption.
Also, someone is likely to put their used masks in pockets and reuse them after a while. However, if permitted, we should wear another mask once the previous one is taken off. Especially during epidemic, good hygiene habits are very important.
N95 mask is actually a kind of respirator. Respirator is a respiratory protective equipment. It is tighter to face than common masks and can filter particles effectively. But, what does N95 mean? N represents “not resistant to oil”, i.e., the respirator can prevent non-oily particles. The figure 95 indicates that the respiration has its filtering efficiency no less than 95%. Some tests prove that N95 respirator can prevent more than 95% particles (0.3μm).
From the design perspective, masks’ prevention performance can be ranked as following: N95>surgical mask>general medical mask>general cotton mask.
If worn correctly, N95’s filtering performance is stronger than that of general masks and medical masks. Even so, N95 cannot completely eliminate risk of infection or death.
But how KN95 differs from N95?
KN95 is a grade regulated by China’s standard GB2626-2006 and N95 by USA standard 43 CFR 84. the technical requirements and testing methods of these two standards are basically the same.
Some researchers studied prevention efficiency and wearing time of N95 respirator and found that: N95 can be worn for 2 days, its filtering efficiency keeps above 95% and respiratory resistance doesn’t increase a lot. But after 3-day usage, its filtering efficiency will decline to 94.7%.
A suggestion given by CDC is that N95 can be reused if masks are not sufficiently supplied and that one we wear is not broken or damaged.
But when the following conditions appear, we should change mask:
1) Respiratory resistance increases obviously;
2) Masks are broken or damaged;
3) Masks cannot fit face tightly;
4) Masks are polluted by blood stains or droplets.
5) Masks are worn when you contact patients.
Some N95 masks have breathing valve and some not. For those who suffer from chronic respiratory diseases, heart disease or other diseases symptomized by dyspnoea, N95 respirator will make their breathing more difficult. In this case, they can use N95 masks with breathing valve. Except easier exhalation, a breathing valve can also lead to less heat accumulation.
The valve is exquisite. Its several-layer covers will be closed during inhalation to prevent particles from entering, and be opened while exhaling to exhaust humid air. Besides, a soft cover inside can make sure that no small particles can enter.
These days, many people have misunderstanding to exhalation valve of N95. They think that masks with exhalation valve cannot protect them. However, a survey on influence of exhalation valve on protecting wearer was released in 2008 and showed that exhalation valve has no effect on masks’ protecting wearers. Simply speaking, N95 with a exhalation valve can protect the wearer but not surrounding persons. If the wearer is a virus carrier, it’s better to not use N95 with exhalation valve. However, to create a bacteria-free environment, wearers please try not to use N95 mask with respirators to avoid exhalation of bacteria or virus.
Mask | N95/KN95 (without valve) | N95/KN95 (with valve) | Surgical mask | Common medical mask | Cotton mask |
Expected result | Also known as N95/KN95 respirator; to filter particles in air effectively and to prevent respiratory infectious diseases | Same as N95/KN95 (without valve) | For medical staff or relevant personnel; To prevent splashing of blood, body fluid or other liquid during invasive operation. | Used in common conditions; To prevent particles (such as pollen) excluding pathogenic microorganisms | To keep out the wind, keep warm or prevent large particles such as dust. |
Filtering performance | To prevent at least 95% small particles (about 0.3μm) | Same as N95/KN95 (without valve) | Medical surgical masks have different filtering efficiency. Generally speaking, they can prevent 5μm particles. The outer fluid layer can prevent droplets. The inner layer is for filtering. | Lacking requirements on their filtering efficiency, or lower requirements than that on surgical mask and medical prevention mask. | To filter large particles such as dust. |
Usage times | For private use; Damaged, out-of-shape, wet, dirty or polluted masks should be thrown away. | Same as N95/KN95 (without valve) | Disposable | Disposable | Repeatedly usable after washing |
Notes | Not suitable for children or the bearded because their face cannot fit N95 tightly. | Same as N95/KN95 (without valve) | / | / | / |
1) Wash hands before wearing mask or avoid contacting inner side of mask with hands. Try not to stain the mask;
2) Make clear the outside, inside, top and bottom of the mask. The printed side is the outside and the end with a metal or sponge strip is the top;
3) Don’t extrude mask with hands;
4) Make sure that the mask fit face perfectly.
All in all, mask is not everything. but correct wearing mask and frequent washing hands can obviously help us prevent virus. If you are virus carrier, please use N95 without exhalation valve to avoid virus spreading from you. Hope all of you to be safe and healthy.
