The prototype of the air filter is a breathing protection device that people use to protect their breathing. According to records, as early as the first century in Rome, people used a mask made of hemp to protect them when purifying mercury. In the long time since then, air filters have also made progress, but they are mainly used as respiratory protection appliances in some hazardous industries, such as the production of hazardous chemicals. In 1827 Brown discovered the laws of movement of tiny particles, and people have a better understanding of the mechanism of air filtration.
The rapid development of air filters is closely related to the development of the military industry and the electronics industry. During the First World War, due to the use of various chemical agents, military gas masks using asbestos fiber filter paper as a smoke filter layer came into being. Glass fiber filter media was patented in the United States in October 1940. In the 1950s, the United States conducted in-depth research on the production process of glass fiber filter paper, which improved and developed the air filter. In the 1960s, HEPA filters came out; in the 1970s, HEPA filters using micro-glass fiber filter paper as the filter medium, the filtration efficiency of particles with a particle size of 013 microns was as high as 99.9998%. Since the 1980s, with the emergence of new test methods, improved use evaluation, and increased requirements for filtration performance, it has been found that HEPA filters have serious problems, so they have produced higher-performance ULPA filters. Countries are still working on research, and it is estimated that more advanced air filters will soon be available.
