Why do HEPA filter have 0.3 micron pore size?
High efficiency particulate air filters are used to maintain the area cleanliness in classified area. Pore
size of these filters is always 0.3 microns.
lHEPA filters use a four-step process to purify air:
1. Initial Particle Removal: Larger particles are captured through sieving and inertial impaction as air
flows into the filter.
2. Fine Particle Filtration: Air passes through a finer mesh of fibers, trapping smaller particles
effectively.
3. Collision Filtration: As air continues through the filter, remaining particles collide with the fibers
and become trapped.
4. Final Output: The air that exits the HEPA filter is highly purified, removing up to 99.97% of
particles, including those as small as 0.3 microns.
The smaller the micron, the harder it is to filter out of the air.To
understand, the human eye detects particles around 10 microns, like pollen or plant spores.
Bacteria, however, can measure as small as 0.3 microns—far beyond the reach of standard filters.
Industrial HEPA filters, capable of capturing particles at this microscopic level, are essential in
environments like pharmaceutical companies, where maintaining sterile air is critical. Bacteria can be
as small as 0.3 microns, which is why 0.3 micron industrial HEPA filters are used in pharma
companies.
What is MPPS in a HEPA filter?
The MPPS is the “most penetrating particle size.” It’s the hardest size of particle to capture.
It’s NOT the smallest particles. The smallest particles (like .01-micron particles) are SUPER easy to
capture (because of Brownian motion). And it’s not the biggest particles either. Big particles like a
grain of sand or a human hair are also really easy to capture (because of the net).
The hardest particle to capture is in between those two—around 0.3 microns. Those particles are
small enough to fit through the filter fibers, but they’re large enough to fly in relatively straight lines.
The most penetrating particle sizes (MPPS) for HEPA filters is the hardest particle size to capture,
often around 0.3 microns
Here's how Brownian motion makes it easier to capture small particles like those around 1 micron in
size:
What is Brownian Motion?
* Tiny particles suspended in a fluid (like air or water) are constantly bombarded by the molecules of
that fluid.
* These collisions cause the particles to move randomly in a zigzag, jerky pattern. This is Brownian
motion.
Why Brownian Motion Helps Capture
* Increased Chance of Contact: The random movement of Brownian motion increases the likelihood
that a small particle will bump into a filter fiber or a surface designed to capture it.
* Reduced Inertia: Larger particles have more inertia, meaning they tend to keep moving in a
straight line. Smaller particles have less inertia, so they are more easily deflected by the random
collisions of Brownian motion, making it easier for them to change direction and get trapped.
Analogy:
Imagine trying to catch a fly in a room. The fly's erratic, unpredictable flight path (like Brownian
motion) makes it more likely to eventually fly into your hand or a spider web.
Important Note: Brownian motion is most significant for very small particles (generally below a few
microns in size). As particles get larger, their inertia increases, and the effect of Brownian motion
becomes less dominant.
HEPA filters are indeed very efficient, capturing 99.97% of particles that are 0.3 microns or larger.
While it's true that 0.03% of particles can still pass through, it's important to understand a few
things:
* HEPA filters are tested at the "most penetrating particle size" (MPPS): This is 0.3 microns. HEPA
filters are actually more efficient at capturing particles smaller than 0.3 microns, which includes most
viruses and bacteria.
* 0.03% is a very small number: In a typical room, this would mean very few particles escaping the
filter.
* Other factors contribute to air quality: Ventilation, room size, and the presence of other pollutants
all play a role.
In summary: While no filter is perfect, HEPA filters provide a very high level of protection against
airborne particles. The 0.03% that may escape is a tiny fraction, and the filters are even more
effective at capturing the very small particles that are of most concern.
