A High-Efficiency Particulate Air (HEPA) filter is a device designed to remove fine particles from the air. The ultimate goal of a HEPA filter is to capture at least 99.99% of particles with a diameter of 0.3 microns, which are among the most challenging to capture. The filter achieves this through several mechanisms:

1. Filter Material: HEPA filters use a dense mesh of fibers, typically made from glass or synthetic materials, to trap particles of various sizes.

2. Particle Capture Mechanisms:

   • Inertial Impaction: Larger particles collide with and are captured by the fibers due to their inertia.
   • Sieve Effect: Medium-sized particles are trapped by the mesh.
   • Diffusion: Very small particles are captured by the fibers due to random motion.

3. Efficiency Standard: To be HEPA certified, a filter must remove at least 99.97% of particles that are 0.3 microns in diameter under specified conditions. This standard measures the filter's effectiveness in capturing various particles.

HEPA filters are widely used in air purifiers, vacuum cleaners, automotive air filters, and hospital operating rooms to improve air quality and prevent harmful particles from entering the respiratory system.