Air Filtration in Cleanrooms
In cleanrooms, air filtration is one of the most critical aspects for maintaining the required cleanliness level, measured by the number of particles per cubic meter of air. The goal is to ensure air purity, which prevents contaminants from interfering with sensitive processes, such as pharmaceutical production, electronics manufacturing, or medical device assembly.
Purpose of Air Filtration in Cleanrooms
The primary role of air filtration is to remove airborne particles (like dust and microorganisms) that could contaminate products or processes. These particles can come from people, equipment, materials, or even the cleanroom itself.
Additionally, cleanrooms are classified by the number and size of particles allowed per cubic meter. For example, in an ISO 5 cleanroom, only 3,520 particles (0.5 microns or larger) are allowed per cubic meter. The filtration system is designed to meet or exceed these stringent requirements.
In a cleanroom, the air is continuously filtered using HEPA filters or ULPA filters. Let’s take a closer look at the types of filters used for air filtration in cleanrooms.
HEPA Filters (High-Efficiency Particulate Air)
HEPA filters capture at least 99.97% of airborne particles that are 0.3 microns in size. This size is considered the most penetrating particle size (MPPS), meaning it is the hardest to filter. HEPA filters are effective at removing larger particles, such as dust, pollen, and most bacteria.
HEPA filters are usually installed in the ceiling or air handling unit, where clean, filtered air is introduced into the room. They are essential for ISO 5 to ISO 8 cleanrooms.
Advantages of HEPA Filters:
- High Efficiency for Common Contaminants – HEPA filters are highly effective at removing a wide range of contaminants, including dust, pollen, mold spores, and bacteria, making them ideal for most cleanroom applications.
- Cost-Effective – HEPA filters are widely used and relatively cost-effective compared to ULPA filters. They provide excellent filtration for most cleanrooms (ISO 5 to ISO 8).
- Versatile – They can be used in a wide variety of industries, including pharmaceuticals, biotechnology, and electronics manufacturing.
ULPA Filters (Ultra-Low Penetration Air)
ULPA filters are even more efficient than HEPA, with the ability to capture 99.999% of particles as small as 0.12 microns. These filters are used in higher-class cleanrooms where even the smallest particles need to be controlled.
ULPA filters are used in extremely critical applications like semiconductor fabrication or nanotechnology, where any particle contamination could damage delicate processes.
Advantages of ULPA Filters:
- Higher Efficiency for Smaller Particles – ULPA filters provide a higher level of particle filtration, capturing smaller contaminants that HEPA filters may miss. This makes them essential for applications where even the smallest particles can cause defects or contamination.
- Ideal for High-Class Cleanrooms – ULPA filters are ideal for cleanrooms classified as ISO 4 or higher, where extremely stringent air purity standards are required.
- Improved Process Quality – By ensuring a higher level of filtration, ULPA filters reduce the risk of defects in sensitive processes like microchip manufacturing or medical device production.
Pre-Filters
Pre-filters are lower-efficiency filters typically installed upstream of HEPA or ULPA filters. They capture larger contaminants such as dust and hair, which could otherwise clog the more expensive and sensitive HEPA or ULPA filters.
Advantages of Pre-Filters:
- Extends Filter Life – By capturing larger particles, pre-filters prevent HEPA and ULPA filters from becoming clogged prematurely, extending their operational life and reducing maintenance costs.
- Cost-Efficient – Pre-filters are less expensive to replace than HEPA or ULPA filters, providing a cost-effective solution for increasing the longevity of the entire filtration system.
Challenges of Air Filtration
- Integrity Testing – HEPA and ULPA filters need regular integrity testing to ensure there are no leaks or breaches in the filter housing. Even a small leak can allow contaminants to bypass the filter.
- Maintenance – Over time, filters become clogged with particles, reducing airflow and increasing energy costs. Regular filter replacement and maintenance are required to ensure optimal performance.
- Air Leaks – Proper sealing of ductwork, filter housings, and cleanroom enclosures is essential to prevent unfiltered air from entering the cleanroom environment.
Air filtration is the backbone of any cleanroom’s environmental control system. The use of HEPA and ULPA filters ensures that particulate matter, including microorganisms, is effectively removed from the cleanroom, maintaining the necessary air purity levels. Understanding the filtration mechanisms, air flow patterns, and cleanliness standards is crucial for designing, operating, and maintaining cleanrooms that meet strict industry regulations.
