In a professional testing organization, how to detect masks?

In the current market, masks can block droplets, and virus protection has gradually become the “hardcore” factor that consumers first consider. In professional testing organizations, this indicator is called filtration efficiency. In a professional testing organization, how is the filtration efficiency tested? What are the key items of qualified masks? This article we will discuss together.

What are the characteristics of masks that can block viruses?

The key part of the mask with the virus protection effect is the filter material. The filtering material mainly has the functions of gravity sedimentation, interception, inertial collision, diffusion, electrostatic adsorption, etc. Under the joint action of various filtering mechanisms, the lowest filtering efficiency exists for particles with an aerodynamic particle size of about 0.3 µm Value, also known as the most easily penetrated particle size (MPPS). The median diameter of sodium chloride particulates used in the filtering efficiency test of mask particulates is (0.075 ± 0.020) μm, the geometric standard deviation of the particle size distribution is not greater than 1.86, and the converted aerodynamic mass median diameter is (0.249 ~ 0.430) µm; the particle size distribution of oily particles is also close; before the particle filtration efficiency test, the mask samples need to be subjected to a constant temperature and humidity pretreatment to ensure that the warm and humid airflow exhaled by the human body during wearing will not cause the mask filtration efficiency to decrease to the standard requirements the following. The size of the new coronavirus is about 120nm, which is the most difficult to filter particles; the size of bacteria is about 3 µm, which is relatively easy to filter. Virus blocking is basically equivalent to particulate filtering efficiency.

The masks we use are generally 3 or more layers. The inner and outer layer materials are mostly polypropylene spun-bond nonwoven fabrics. The particle filtration efficiency of spun-bond nonwoven fabrics is very limited, mainly acting as mechanical support; the middle layer is the electret polypropylene melt-blown nonwoven cloth material, this material can use static electricity to adsorb particulate matter, thereby greatly improving the filtration efficiency. In addition, we also recommend PTFE-coated membrane filter material as an alternative to melt-blown non-woven fabrics. The filtering mechanism of this material is mechanical pore size sieving and filtration. The microporous structure on the surface of the membrane is used to filter particulates. The filtration efficiency and pressure difference are The electret polypropylene melt-blown nonwoven fabric material is equivalent.

Can I buy masks such as “disposable masks” and “protective masks” on the market? Has the mask expired?

Regardless of the name of the mask, you can judge whether it is suitable for your use from the following points.

First look at the material. The core of the mask to block the virus is the filter material. At present, the most used is electret polypropylene melt-blown non-woven fabric. Consumers can cut the masks they have bought to see if there is a fluffy white non-woven fabric on the inner layer that feels soft to the touch. If there are only loose needle-punched cotton or cotton cloth, the filtration efficiency will definitely not meet the national standards. Claim.

The second real person tried it on and felt whether the nose clip and ears were comfortable after wearing the mask and whether there was any obvious discomfort in skin contact; carefully observe whether there is a gap in the nose and chin, or wear the mask and cover the mask with your hand, Breathe quickly to see if the mask is leaking.

Third, look at the packaging. Masks are divided into three categories: medical, industrial, and civilian. Medical masks are used as medical equipment management masks. Product categories include GB 19083-2009 medical protective masks, YY / T0969-2013 disposable medical masks, and YY0469-2011 medical surgical masks. For medical masks, it depends on whether there is information such as a medical device production license on the packaging. Industrial masks, also known as labor protection masks, mainly implement Chinese standards GB 2626-2006 (such as KN90, KN95, etc.), American standards NIOSH (such as N95, N99, etc.) and European standards EN 149-2001 (such as FFP1, FFP2, etc.)

Civil masks, mainly implement the Chinese standard GB / T 32610-2016 (protection effect C level, D level, etc.). In addition, protective masks for emergency production in Zhejiang Province and masks that implement the standard of T / ZFB 004-2020 “Children’s Masks” also have good protective effects. Masks such as “disposable masks” and “disposable protective masks” on the market depend on the specific implementation standards; if they are enterprise standards, see if the filtration efficiency is clearly stated.

Attention should also be paid to the validity period. Over time, the static electricity on the filter material will gradually weaken or even disappear. For example, the original particulate filtering efficiency is 95%, and the filtering efficiency will drop to less than 50% after the static electricity disappears.

Good quality electret polypropylene melt-blown nonwoven fabrics can be stored in a cool and dry place, and the static electricity can be maintained for 2 years or even 5 years. The static electricity of poor quality nonwoven fabrics can only be retained for one month or even shorter.

 

There are many consumers on the Internet who use self-made methods to evaluate masks, such as pouring water to see filter efficiency, burning melt-blown cloth, etc. Some people think that thicker and larger breathing resistance is better. Can these methods detect the quality of masks?

Soil methods such as pouring water and burning are ineffective. The core indicators of the mask, such as filtration efficiency, protective effect, leakage rate, respiratory resistance /ventilation resistance, etc., must be professionally tested. A video says that after the mask is disinfected with alcohol, the water can pass through, indicating that there is no filtration efficiency, which is completely wrong. Alcohol immersion is a hydrophilic treatment phenomenon in membrane filtration and has nothing to do with whether aerosol particles can be filtered.

Masks with higher filtration efficiency tend to have higher respiratory resistance, and overprotection is not recommended.

There is a misunderstanding here. Some people think that the thicker the filter material, the higher the filtration efficiency. The filtering efficiency of polypropylene melt-blown non-woven fabrics is largely determined by the effect of electrostatic electret treatment. The melt-blown nonwoven fabric with good electret effect can reach the requirement of 90% filtration efficiency when the weight is 25, while the melt-blown non-woven fabric without the electret treatment has a filtration efficiency of less than 70% when the weight is 60.

The key to a qualified mask is good protection. The selected material must have good particle filtering performance, and the mask style made can closely fit the human face during the wearing process without obvious leakage. Secondly, it is comfortable to wear and has low breathing resistance. Some manufacturers on the market use multiple layers of filter materials or air-impermeable materials to increase the filtering efficiency of the mask unilaterally, which greatly increases the breathing resistance of the mask. Finally, it is safe and reliable.

The raw materials should be non-toxic and harmless, and must not have pathogenic bacteria. The mask should not be damaged or deformed during the normal service life, and there should be no obvious pressure or pain during wearing.

For the filtering efficiency of the key items of masks, what method is used to detect the filtering efficiency of masks? What is the principle? Different types of masks (protective/medical) have filtration efficiency requirements, is there any difference in their testing process?

Use sodium chloride salt particulate matter and dioctyl phthalate or equivalent oil particulate matter (such as paraffin oil) for particle filtration efficiency testing, where salt particulate matter mainly reflects microorganisms, coal dust, cement dust, acid mist The filtering effect of particulate matter, etc., mainly reflects the filtering effect of particulate matter such as oil fume, oil mist, asphalt smoke,  and coke oven smoke. Medical plane masks mainly evaluate the bacterial filtration efficiency of Staphylococcus aureus. The bacterial filtration efficiency requires more than 95%. Bacteria filtration is relatively easy. According to the YY0469 standard, basically the particulate filtration efficiency is above 80%, and bacterial filtration can be satisfied; when the particulate filtration efficiency is above 90%, the bacterial filtration efficiency can exceed 99%. The filtering project only evaluates the performance of the filter material of the mask body. At present, the filtration efficiency that everyone often talks about refers to the filtration efficiency of particulate matter.

The principle of particle filtration efficiency detection and testing is very simple. The particle generator generates aerosols of different properties and concentrations to simulate polluted air, and then collects the mass concentration of the particulate matter before and after the mask filtration to obtain the value of the particle penetration rate. -Particle penetration rate. Carry out a load test according to the requirements of different standards. Mask wearing requires a certain amount of protection time. The deposition of sodium chloride particles will have an electrostatic shielding effect, and the deposition of oily particles will have an electrostatic attenuation effect. Therefore, the change of the filtration efficiency of the mask during use is investigated, that is, the load filtration efficiency test

The filtration efficiency test parameters of medical protective masks, labor protection masks. and civil masks are basically the same. All the masks are tested. The test flow rate is 85L / min, and the technical requirements are slightly different. Medical protective masks only assess the initial filtration efficiency of salty particulates; labor protection masks require separate assessments requiring a particulate load of 200 mg; and civilian masks require simultaneous assessment, requiring a particulate loading of 30 mg.

The filtration area of ​​the medical plane mask is 100cm2, and the test flow rate is 30L / min.

 

What other key items affect the quality of masks?

Another key item for mask detection is the leakage rate, protective effect, or tightness. This project refers to the filtering effect of “real” particulate matter played by the human body in the process of wearing a mask. The filtering efficiency of the mask is determined by the performance of the filter material selected for the mask. In addition to the filtering efficiency of the mask itself, the design of the mask is also a key influencing factor. Once there is a large gap between the mask and the wearer’s face, particulate matter will leak from the gap, causing protection failure, and it is likely that the filtration efficiency will pass and the protection effect will not pass. During the test of this project, the concentration of particulate matter inside and outside the mask is mainly collected and calculated.