Wearing masks can effectively filter the air inhaled into the lungs. When pedestrians, medical personnel and factory operators need to isolate dust, viruses and toxic gases, it is very important to choose appropriate masks. Protective filter mask can effectively filter out harmful substances in the air.
At present, there are many types of masks circulating in market, including protective filter masks against dust, toxic gas and bacteria. According to the specific needs of personnel in various industries, the state has issued corresponding mask standards to standardize the domestic mask market. The standards of protective filter masks implemented in China are mostly mandatory product standards, and the filtration efficiency is an important test item. Therefore, it is very important to study the mask filtration efficiency of protective filter masks.
Classification and standard comparison of 01 masks
Masks can be divided into N and P (or kn and KP) according to different filtration performance. N (or KN) is only suitable for filtering non oily particles, and P (or KP) is suitable for filtering oily and non oily particles.
NIOSH divides the particulate respirator or or filter element into three categories: n, R and P according to the nature of the protected object and the length of time for preventing oily particles: n is used to protect non oily particles; Class R and class P can be used to protect non oily particles and oily particles (class R filter elements have a shorter service time limit than class P filter elements, generally 8h, while class P filter elements have a longer service time, which is generally recommended by the manufacturer).
NaCl aerosol is used to detect the filtration efficiency of salt particles, while DOP or paraffin oil or other oil particles with equivalent properties are generally used to detect the filtration efficiency of oil particles.
02 filtration mechanism
(1) Brownian motion: because the particle size is too small, it is vulnerable to the continuous impact of other gas molecules, resulting in their motion trajectory is irregular Brownian motion and adsorbed on the fiber surface. The smaller the particle, the stronger the effect.
(2) Interception: the particle size is too large to penetrate the gap of the fiber, and then directly captured by the fiber surface. The larger the particle size, the better the effect.
(3) Inertial impact: particles with different mass and high speed produce different inertia, so that particles cannot bypass the filter material surface with the air flow and leave the flow force line, collide with the fiber surface and fall. The greater the mass and the faster the speed of particles, the stronger the force.
(4) Electrostatic adsorption: it is charged for the fiber and induces very fine particles to adsorb on the fiber surface. It is easier to attract particles with smaller particle size and lighter mass.
(5) Sedimentation: direct sedimentation caused by the gravity of particles and captured by filter material, the greater the mass, the more opportunities.
03 test method