Types of Air Filters Used in Pharmaceutical Plants

Pre-filters

Target contaminants: Large airborne particles with a diameter of 5 micrometers or more, including dust, hair, fibers and pollen.

Efficiency class: Under EN 779, pre-filters are normally classified as G1-G4. G4 is commonly used and provides an efficiency of at least 90% for 5-micrometer particles.

Filter materials:

Filter media: Nonwoven fabric, nylon mesh, wire mesh and, in limited applications, activated-carbon fiber for odor removal.

Frame: Cardboard, aluminum or galvanized-steel frames. Pharmaceutical plants generally use corrosion-resistant aluminum or galvanized frames to prevent rust contamination.

Applications:

Used as the first filtration stage in an air-conditioning system to protect downstream medium-efficiency and high-efficiency filters and extend their service life.

Installation location: At the fresh-air inlet or upstream of the return-air section of the air-handling unit.

Pharmaceutical requirements: The media must meet basic GMP requirements for non-shedding fibers so that fragments do not enter the clean area. Low-lint nonwoven or synthetic-fiber media are normally selected.

Medium-efficiency air filters

Target contaminants: Particles 1 micrometer or larger. These filters capture fine dust and some microorganisms, such as fungal spores, that pass through the pre-filter.

Efficiency class: F5-F9 under EN 779. F8-F9 filters are commonly used in pharmaceutical plants; F8 efficiency is at least 90% for 1-micrometer particles.

Filter materials:

Filter media: Glass fiber, polyester fiber (PET) or polypropylene (PP), usually in a pleated structure that increases the filtration area and reduces resistance.

Frame: Aluminum, galvanized steel or plastic, selected for the required temperature and corrosion resistance inside the air-handling unit.

Applications:

Used as the second filtration stage to further clean the air and reduce the load on the HEPA filter.

Installation location: Downstream of the air-handling-unit fan and upstream of the HEPA filter.

Pharmaceutical requirements: The media must have adequate dust-holding capacity and resist moisture in humid environments such as cleanroom air-conditioning systems. Antimicrobial filter media may be selected for some areas, including biopharmaceutical clean zones.

HEPA filters

HEPA stands for High Efficiency Particulate Air.

Target contaminants: Particles 0.3 micrometers or larger. HEPA filters provide at least 99.97% efficiency against microorganisms such as bacteria and viruses and against submicron dust, making them the core barrier for clean-area air purification.

Efficiency class: H10-H14 under EN 1822. H13, which provides at least 99.97% efficiency at 0.3 micrometers, is commonly used in pharmaceutical clean areas.

Filter materials:

Filter media: Ultrafine glass-fiber paper, the mainstream option, or membrane-coated polypropylene paper. The media is pleated and sealed with an adhesive such as polyurethane to prevent leakage.

Frame: Aluminum-alloy or stainless-steel frames, both of which resist corrosion and are suitable for clean areas.

Applications:

Installed at terminals in pharmaceutical clean areas, including cleanroom supply outlets, biosafety cabinets and isolators, to directly control indoor air cleanliness in accordance with GMP Grade A and Grade B requirements.

Special pharmaceutical requirements:

The filter must pass an integrity test, such as a PAO leak test, to confirm that it has no leaks.

The media must withstand high temperatures when required. Some sterilization applications require resistance to moist-heat sterilization at 121 degrees Celsius or to chemical disinfection.

The seal between the frame and filter paper must meet food- and pharmaceutical-grade requirements and must not release contaminants.

ULPA filters

ULPA stands for Ultra Low Penetration Air.

Target contaminants: Particles 0.12 micrometers or larger, with an efficiency of at least 99.999%, which is higher than that of HEPA filters.

Efficiency class: U15-U17 under EN 1822.

Applications:

Used in pharmaceutical areas with exceptionally demanding cleanliness requirements, such as isolator operating zones for sterile active pharmaceutical ingredients and core cleanrooms for vaccine production that must meet GMP Grade A or stricter requirements.

Special considerations when selecting filters for pharmaceutical plants

Compliance with GMP and industry standards:

Filter performance must meet the requirements of Good Manufacturing Practice for controlling airborne particles and microorganisms in clean areas. For example, a Grade A area must contain no more than 3,520 particles per cubic meter at 0.5 micrometers or larger and no viable microorganisms.

Give preference to products certified to standards such as ISO 14644 and applicable FDA and USP requirements.

Resistance to sterilization and disinfection:

Filters used in biopharmaceutical workshops, including vaccine and blood-product production areas, must withstand steam-in-place (SIP), vaporized hydrogen peroxide (VHP) or ultraviolet disinfection. Their materials must remain stable, with options such as stainless-steel frames and chemically resistant filter paper.

Low leakage and integrity:

HEPA and ULPA filters must undergo factory leak testing and be tested again after installation, using methods such as PAO aerosol or DOP testing, to ensure that no bypass leakage exists.

Balance between resistance and energy consumption:

Excessive filter resistance increases the energy consumption of the air-handling fan. Filtration efficiency and resistance must therefore be balanced, for example by choosing low-resistance HEPA media. Replace the filter regularly, typically when resistance reaches 1.5-2 times the initial resistance.

Compatibility with the air-conditioning system:

Filter dimensions and airflow capacity must match the supply airflow of the air-handling unit. As a general rule, rated airflow should be at least 1.2 times the actual operating airflow. This helps prevent excessive airflow from reducing filtration efficiency or damaging the filter.

Summary

Air filters in a pharmaceutical plant should follow a staged-filtration and progressive-purification strategy: pre-filters protect the system, medium-efficiency filters extend HEPA service life, and HEPA or ULPA filters provide final cleanliness control. Selection should be based on the cleanliness grade of the production area (Grade A, B, C or D), process requirements such as sterilization, and environmental conditions such as temperature, humidity and corrosiveness. Choose GMP-compliant products with stable, traceable performance, and give equal attention to post-installation integrity testing and routine maintenance.