The choice of mask has three principles:
First, the mask of the dust barrier efficiency. The barrier efficiency of the mask is based on its resistance to fine dust, especially for respiratory dust below 5 microns. Because the diameter of the dust can be directly into the alveolar, the greatest impact on human health. General gauze masks, the principle of its resistance is mechanical filter, that is, when the dust hit the gauze, after - layers of the barrier, some large particles of dust in the sand cloth. However, for some fine dust, especially less than 5 microns of dust, will be from the gauze in the mesh through, into the respiratory system. There are some dust masks abroad, the filter material by the permanent static electricity of the fiber composition, those less than 5 microns of breathing dust through the filter in the process of being attracted by electrostatic attraction in the filter to capture the fine Dust, really play a role in blocking dust.
Second, the degree of mask and face shape close. The air is like water, where the resistance is small and the first to flow. When the shape of the mask and the face is not close, the air of the dangerous things will never leak into the same place, into the human respiratory tract. So, even if you choose the filter no matter how good the mask. Also can not protect your health. Now many foreign regulatory standards, workers should be regularly carried out mask adhesion test. The purpose is to ensure that workers use appropriate masks and wear masks according to the correct steps.
Third, wear comfortable. Require breathing resistance to be small, light weight, wear health, easy maintenance. So that workers will be willing to wear and improve their work efficiency in the workplace. Now the maintenance-free masks, do not have to clean or replace the parts, when the resistance to dust or mask damaged after the discard, so that both the health of the mask and remove the workers to protect the time and energy. And many masks are used arched shape, both to ensure that the shape of the face with a good fit in the nose and mouth to retain a certain space, comfortable to wear.