- People not suitable for masks
(1) People with heart or respiratory problems (such as asthma and emphysema)
(2) Pregnant women
(3) People with dizziness, dyspnea and skin sensitivity after wearing
2. Characteristics of several kinds of masks sold on the market
Advantages of cotton mask: reusable and washable
Disadvantages: There is saliva on the inner surface of the mask where it contacts the nose and mouth. If you do not wash your mask very often, the mask is prone to bacteria, which does not meet hygiene requirements. Cotton mask fibers are generally very thick, can not effectively filter small particles, and most of them fail to meet international safety standards, thus their protection effect is not guaranteed. Gauze masks are almost useless, and the air leaks on both sides of the nostrils are too large.
N95 face-mask: It can prevent the wearer from being infected, but it cannot prevent the patient from transmitting the virus to others.
Surgical mask: Although the protective effect is not as good as that of N95, it can prevent patients from transmitting the virus to others.
3. Is the smaller the dust, the harder it is to be filtered by the mask?
We tend to think that the smaller the dust, the harder it is to be filtered, but this is a specious concept. In terms of filtration theory, there are mainly five methods for filtering dust:
1) Brownian Diffusion –The smaller the particle, the stronger the effect.
2) Interception –The bigger the particle, the better the effect.
3) Inertial Impaction –The bigger the particle, the better the effect.
4) Gravitationl Settling –The bigger the particle, the better the effect.
5) Static –The smaller and lighter the particle, the easier it is to be attracted.
It can be seen from this that the smaller the dust, the stronger the effects of 1 and 5; the greater the dust, the better the effects of 2, 3 and 4, so it’s not that the smaller the dust, the harder it is to be filtered. The most difficult particle to be filtered is simply called MPPS (Most Penetrating Particleize). MPPS are generally 0.3 microns in size (another is 0.6 microns). No matter the certification standards of European standard EN149, American NIOSH and Australian AS1716, MPPS is adopted for testing. As long as you buy a certified mask, it can protect your respiratory system.
- How to select a suitable mask?
There are three principles in selecting a mask:
(1) Dust resistance efficiency of mask. The dust blocking efficiency of mask is based on its blocking efficiency for fine dust, especially respiratory dust below 5 microns. As dust of this particle size can directly enter alveoli, which has the greatest impact on health. As far as the gauze mask is concerned, its dust blocking principle is mechanical filtration, that is, when dust collides with gauze, it blocks some large particles of dust in the gauze by means of layers of blocking. However, for some fine dust, especially dust less than 5 microns, it can pass through the mesh of gauze and enter the respiratory system. At present, there are some respirators abroad, whose filter material consists of fibers filled with permanent static electricity. Those respirable dust less than 5 microns are attracted by static electricity and absorbed in the filter material during passing through the filter material, and the fine dusts are captured, which really plays a dust-proof role.
(2) The tightness between the mask and the face. Air is just like water flow. Where there is little resistance, it flows first. When a mask does not fit with the human face, dangerous substances in the air will enter the respiratory tract from the non-closed place. Then, even if you select the mask with the best filter material, it cannot protect your health.
(3) Comfort. A mask must be light, hygienic and easy to maintain, with small respiratory resistance.
Use of masks
- Use of common mask
The mask must be suitable in size and worn in a right way in order to be protective. The masks on sale are generally divided into rectangular and cup-shaped. Rectangular masks must have at least three layers of paper to have a protective effect. The user should press the wire on the mask on the nose bridge, and then along the nose bridge to spread the whole mask, so that the mask can play a protective role. Children can wear a rectangular surgical mask because it does not have a fixed shape. If well bound, the mask can adhere to the children’s face. Make sure that a cup mask has enough density after being attached to the face, and the exhaled air will not leak out, so that it can play a protective role. When wearing a cup mask, cover both hands with the mask and try to blow air to check whether air is leaking from the edge of the mask. If the mask is not tight, wear it again.
- How to wear a mask correctly
- Place the mask in your palm and place the nose metal strip toward your fingertips so that the headband hangs down naturally.
(2) Put on a mask, with the nose metal strip facing upward and close to the face.
(3) Place the upper headband of the mask behind your head, then pull the lower headband over your head, then place it behind your neck, and adjust it until you feel comfortable.
(4) Along the metal strip of the noise bridge, slowly press it inward with your fingertips from the middle to both sides until it is close to the nose bridge.
(5) Cover mask with both hands and test positive and negative pressure. Positive pressure test is that you cover the mask with both hands and exhale vigorously. If air overflows from the edge of mask, the mask is improperly worn and the headband and nose bridge metal strip must be adjusted again. Negative pressure test is that you cover the mask with both hands, exhale vigorously, and the center of mask will sink. If air enters from the edge of the mask, the mask is not properly worn. The headband and nose bridge metal strip must be adjusted again.
(6) Function of the breathing valve: In the working environment with damp heat, poor ventilation or large workload, wearing a respirator with the respiratory valve can make you feel more comfortable when exhaling. The action principle of the breathing valve is that when exhaling, the positive pressure of the exhaust gas will blow off the valve plate, quickly remove the exhaust gas from the body, reduce the muggy feeling when using mask, and the negative pressure will automatically close the valve when inhaling to avoid inhaling the pollution of the external environment.
3. When to replace a mask
(1) The mask is contaminated, such as blood stains or droplets and other foreign bodies;
(2) The user feels that the respiratory resistance is larger;
(3) The mask is damaged.
(4) Under the condition that the mask is tightly closed to the user’s face and the user feels great respiratory resistance, the mask should be replaced when the filter cotton is covered with dust particles.
(5) Under the condition that the mask is tightly closed to the user’s face, the mask should be replaced when the user smells toxic substances.
4. Mask should not be worn for long
From the point of view of human physiological structure, due to the strong blood circulation of nasal mucosa and tortuous channels in nasal cavity, nasal hair constitutes a “barrier” for filtration. When air is sucked into the nostrils, the airflow forms a vortex in the tortuous passage, which heats the airflow sucked into the nasal cavity. There is a test showing that when cold air at -7℃ is sucked into the lungs through the nasal cavity, the airflow is heated to 28.8℃, which is very close to human body temperature. If you wear a mask for a long time, the nasal mucosa will become fragile and the nasal cavity will lose its original physiological function, so you cannot wear a mask frequently. A mask can only be worn in special conditions, such as places with large population and no air circulation. Certainly, when you are in the open, it is necessary to wear a mask in order to resist sandstorm and cold, or when you move in an air polluted environment, you should wear a mask, but the wearing time should not be too long. In addition, a mask should be worn in public places where there may be a large number of pathogenic bacteria during the flu season. Wearing a mask is only one of the ways to prevent respiratory infectious diseases, but the most important thing is to keep good living habits.
- How to keep a mask clean
The outer layer of mask often accumulates a lot of dirts such as dusts and bacteria, while the inner layer blocks exhaled bacteria and saliva. Thus, the two sides of mask cannot be used alternately, otherwise the dirt on the outer layer will be sucked into the human body and become the source of infection. When the mask is not in use, it should be folded and put into a clean envelope, and the side close to the nose and mouth should be folded carefully. Do not slip the mask into your pocket or hang it around your neck. If the mask is wetted by exhaled hot air or saliva, its function of blocking bacteria will be greatly reduced. Therefore, at ordinary times, it is best to prepare more masks so that they can be used alternately. The mask should be changed and washed once a day. When washing, scalding it with boiling water for 5 minutes, then gently rubbing with hands. After washing, expose it to the hot sun. Activated carbon masks and disposable masks do not need to be cleaned.
- Mask size
After wearing a mask, it should cover most of the area below the mouth, nose and orbit. A mask is generally 13cm wide and 17cm long. If the mask is too small, germs, dusts and dirts will easily enter the mask from the edge of mask or the gap between the two sides of nose, thus reducing the filtering effect of mask. The main filtering area of mask is on the nose because the mouth is usually closed when people do not speak. However, when people wear a mask, they expose nostrils outside the mask in order to breathe smoothly. Thus the mask cannot serve as a “barrier” to protect their respiratory tract.
How to wear an N95 face-mask correctly:
1. Loosen the headband every 2 to 4 centimeters, pass your hand through the mask headband, and move your nose metal strip forward.
2. Put on the mask and attach it to your face, place the upper headband of the mask behind your head, then pull the lower headband over your head and behind your neck, adjust the headband until you feel comfortable.
3. Along the metal strip of the noise bridge, slowly press it inward with your fingertips from the middle to both sides until it is close to the nose bridge.
4.Cover mask with both hands and test positive and negative pressure. Positive pressure test is that you cover the mask with both hands and exhale vigorously. If air overflows from the edge of mask, the mask is improperly worn and the headband and nose bridge metal strip must be adjusted again. Negative pressure test is that you cover the mask with both hands, exhale vigorously, and the center of mask will sink. If air enters from the edge of the mask, the mask is not properly worn. The headband and nose bridge metal strip must be adjusted again.
Characteristics of various masks:
- Mask (N95): Get approval of National Institute for Occupational Safety and Health（NIOSH）. The N95 mask can filter particles as small as 0.3 micron in diameter. In the test, the success rate was 95% for blocking the particles with a diameter of 0.075 microns. The diameter of coronavirus pneumonia (SARS) virus is about 0.1 to 0.12 microns.
2. Surgical mask: Made of three layers of “non-woven”, suitable for operating rooms; can block particle with a diameter of more than 4 microns.
3. Active carbon medical mask: The most important function of active carbon is to isolate flavor, not to prevent bacteria and viruses, and respiratory resistance will increase, with 98% of bacterial isolation function.
4. Dust mask: The main function is to prevent dust, but its function of preventing bacteria is average.
5. Paper mask: Can block larger particles. Viruses less than 5 microns in diameter can easily enter the inside of the mask, with limited bacteria isolation function.