HEPA = High Efficiency Particulate Air filter.
Its role in a cleanroom is to scrub the air so that particles—especially microscopic ones—don’t float around and settle on your production surfaces, mushroom spawn, or sensitive devices.
Particle removal efficiency:
A true HEPA removes 99.97% of all particles with a diameter of 0.3 microns (that’s about 1/300th the width of a human hair). If it can handle 0.3 µm particles, it’s even more effective on both larger and smaller sizes due to how fluid dynamics work (fun paradox!).
Target contaminants:
Air passes through a dense mat of randomly arranged fibers (usually glass microfiber). Three different mechanisms trap particles:
0.3 microns is the “most penetrating” size: too big for zigzagging diffusion, too small for easy impaction—so if the filter catches those, it catches everything else even better.