The mask can absorb and block smoke, fog, dust, bacteria and other harmful aerosols to help the body isolate harmful substances and purify the air inhaled. The masks used for different purposes have different design requirements and quality evaluation indicators.
It was these angels in white who fought on the front lines against great pressure and danger. The mission and responsibility of the Charge in this battlefield, where there is no smoke, is for them to guard Wuhan and China.
According to GB2626-2006, filtration efficiency is defined as the percentage of particulate matter removed by the filter element under the specified test conditions, which is a fundamental element in determining the performance of medical-surgical masks.
Item 4.6 of the YY0469-2011 standard requires that the bacterial filtration efficiency (BFE) of medical-surgical masks should be not less than 95% and the filtration efficiency (PFE) for non-oily particles should be not less than 30%.
Classical filtration theory points out that the filtration mechanisms that play a major role in the filtration efficiency of mask materials are the interception effect, inertia effect, diffusion effect, gravity effect and electrostatic effect. It is not that the smaller the particle the more difficult it is to filter out due to the combined effect of the five effects. Therefore, the most permeable particles are used in the test to accurately reflect the filtration efficiency of the filter media.
For example, gauze masks are made of ordinary skimmed gauze or ordinary gauze, non-woven masks are made of meltblown fiber, charge meltblown fiber and other non-woven fabrics, and composite masks are made of a variety of filter materials, such as carbon fiber, non-woven fabric and gauze composite, etc.
The filtration efficiency and resistance of gauze are low, while the filtration efficiency and resistance of general nonwovens range from 2.8% to 99.8% and 9 to 157 Pa respectively; the filtration efficiency and resistance of some electropolar masks are 80.6% to 99.9% and 4 to 72 Pa respectively.
Microorganisms such as bacterial viruses do not exist alone in the air, they adhere to dust, droplets and form aerosols. The filtering mechanism of the media to particulate matter also applies to microorganisms.
The particle filtration efficiency of products that do not pass bacterial filtration efficiency may not necessarily pass because the mechanism of action of the filter media is the result of the combined action of five effects.
In addition to providing effective protection, masks should be worn in such a way that the wearer is comfortable, and therefore the technical specifications in the Medical-Surgical Mask Version 2 standard relate to gas exchange items.
YY0469-2011 modifies the technical requirements and test methods for gas exchange compared to the YY0469-2004 standard, retaining only the pressure difference term.
In the 2011 version of the standard, item 4.7 requires that the test be performed at a flow rate of 8 L/min with a pressure difference Δp not greater than 49 Pa for gas exchange on both sides of the mask.
Differences in filter media determine the test results of filtration efficiency, enterprises should consider the comprehensive performance indicators when choosing filter media, can not be the pursuit of filtration efficiency at the expense of pressure difference (comfort).
Therefore, the choice of a suitable filter media is a prerequisite for the production of a qualified mask, it is recommended that manufacturers in the production of medical and surgical masks when selecting the appropriate filter media, not only should consider the filter efficiency of the filter media, but also consider its resistance performance.