HEPA filters filters (civilian)

What does HEPA mean? Where does it come from?

High Efficiency Particulate Air (HEPA) stands for High efficient particular Air and is defined as a filter capable of capturing 99.971 TP3T percentage of 0.3 micron particles. Although HEPA industry standards and certification accreditation mechanisms were not established until 1983, the development of HEPA filters can be traced back to World War II, when U.S. scientists at the Manhattan Project created the first HEPA filters to capture radioactive particles released during the manufacture of atomic bombs.

So why 0.3 microns?

（The (0.3) micron is known to scientists as the MPPS, or Most Penetrating Particle Size (a typical human hair is about 50-150 microns in diameter), so an HEPA filter can capture dust hundreds of times thinner than that. Scientists have found that particles of this size are more likely to evade air filters than larger or smaller particles, and we'll analyze why later. What are HEPA filters made of? How do they work?

Most modern high-efficiency air filters consist of interlaced glass fibers that are twisted and turned in countless directions to form a maze of fibers. As particles pass through this network, they stop circulating in the following manner:

DIRECT IMPACTION: Large particles of contaminants, such as certain types of dust, mold and pollen, travel in straight lines, collide with the fibers and adhere to them.

Sieving (SIEVING): The airflow carries a particle between two fibers, but the particle is larger than the gap and is therefore trapped. INTERCEPTION: The airflow is flexible enough to reroute around the fibers, but due to inertia, the particles continue to move along their path and stick to the sides of the fibers.

DIFFUSION: Small, ultra-fine particles move more erratically than larger particles, so they are more likely to impact and stick to the fiber.

There are also air purifiers that use a combination of technologies (activated carbon, ionization, ozone, UV, etc.) while others use only one technology.