What particles in the air do HEPA filters mainly remove?

This question may seem basic, but it often goes awry in project communication. Some people think that HEPA can solve all problems in the air, while others only know that it can trap dust, but they can’t tell what exactly it traps.

HEPA targets particulate matter. Dust, smoke particles, fibers, and microorganisms partially attached to the particles are its working scope. Odors, volatile organic compounds, acidic or alkaline gases are gaseous pollution and are not within the scope of HEPA treatment.

Particulate matter is divided according to particle size and has different filtration mechanisms.

HEPA filtration is not a simple 'sieve' logic. Its interception of particles of different sizes relies on the combined action of several mechanisms.

Larger particles (usually several microns or more) inertial collision and interception . are captured by the filter fiber mainly through Particles of medium size rely on the diffusion effect - the particles undergo Brownian motion and collide with the fibers to be adsorbed. The most easily penetrated particle size is the particle size in between, usually around 0.1 to 0.3 microns. This is why HEPA testing usually chooses 0.3 microns as the benchmark particle size.

There are practical implications for understanding this: filtration efficiency is not the same for all particle sizes. If the project focuses on particles of a specific particle size, the efficiency data of the product at that particle size should be checked when selecting, rather than just looking at a general grade.

The relationship between microorganisms and particles

Microorganisms such as bacteria and fungal spores are usually in the micron range and can be intercepted by HEPA. But note that they are intercepted as particles, not killed. The filter intercepts microorganisms, which may still survive on the filter material.

Viruses are smaller, usually much smaller than 0.3 microns, and HEPA interception efficiency alone is limited. However, viruses often attach to droplets or dust particles, and these carriers can be intercepted. In situations involving biological safety, filter selection and maintenance must follow special risk control requirements and cannot be judged solely by filtration efficiency.

Gaseous pollutants require separate treatment

This is the most confusing point when choosing.

HEPA does not handle gases. Odors, solvent volatiles, acid gases, and ammonia in the workshop require chemical filtration or other treatment methods. If there are both particulate matter and gaseous pollutant control objectives in the project, they should be listed separately in the plan and each treatment section should be configured, rather than expecting to increase the HEPA level to solve the problem.

The chemical filter used together processes gaseous molecular pollutants. The specific configuration needs to be confirmed according to the type and concentration of pollutants. Please refer to HEPA/ULPA air filters and supporting product information.

The filtering effect depends on the test conditions

The efficiency data on the product report is obtained under the specified test air volume, dust generation method and testing conditions.

The on-site air volume exceeds the applicable range of the product, the installation frame leaks air, and the airflow bypasses the filter material, which may make the actual effect different from the report. When checking the filtration effect, the air volume, resistance, sealing and installation position should be looked at together.

For matching FFU fan filter unit system, the filter element is part of the air path of the unit, and the actual air supply effect is also affected by the working point of the fan. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space, and the airflow organization has a more obvious impact on the filtration effect. It is recommended to consider the internal structure of the equipment when selecting.

The actual order of judgment in the project

When encountering particle control requirements, it is recommended to sort them out in this order:

First, make it clear what you want to control - whether it is dust, smoke, microorganisms, gaseous pollutants, or a combination of several categories. Then determine the target particle size and concentration requirements. Then enter the filter level and system selection.

If the order is reversed, it is easy to choose a high-grade filter element, only to find that it is gas that needs to be controlled; or to install HEPA, only to find that the reason why the room particles are not up to standard is due to sealing or air volume problems, not insufficient filter grade.

involving In the case of ULPA ultra-high-efficiency filters , they still deal with particulate matter, but their ability to intercept smaller particles is stronger, and the processing logic of gaseous pollutants remains unchanged.

About Aili Industrial’s filtration solution package

Aili Industrial produces HEPA/ULPA filters and supporting FFU fan filter unit , EFU and high-efficiency air supply outlet. For projects that require the control of both particulate matter and gaseous pollutants, the configuration of the filter section can be discussed at the planning stage.

It is recommended for new projects to provide cleanliness targets, types of pollutants to be controlled, air volume and installation location to facilitate confirmation of appropriate filtration and air supply configurations. Specific performance is subject to product technical data and project acceptance results.