Cleanroom Air Filters: Controlling Contamination in Controlled Environments
Cleanrooms require air filters to prevent contaminants from entering through their HVAC systems. These environments are carefully controlled in terms of temperature/humidity, pressure, and particulate levels, which are critical for optimal operational performance. Cleanrooms are designed based on the cleanliness level required by specific manufacturing processes. In the semiconductor industry, for example, where microchips are manufactured, air filtration must be highly efficient because chips are extremely sensitive to particulates. Small particles can wedge between the conductive circuits on the wafers during processing.
How Is a Cleanroom Controlled?
High-Efficiency Particulate Air (HEPA) filters are highly effective in controlling contamination. They remove particles as small as 0.3 microns and are widely used in pharmaceutical facilities. ULPA (Ultra-Low Penetration Air) filters can capture particles smaller than 0.12 microns and are commonly used in semiconductor manufacturing environments.
The Importance of Filters in Cleanrooms
Managing contamination inside a cleanroom involves several activities, and the role of HEPA or ULPA filters is critical. HEPA filters must have a minimum efficiency of 99.97% for 0.3-micron particles. This efficiency standard was established by the U.S. Department of Energy and defines what qualifies as a true HEPA filter.
How Do High-Efficiency Air Filters Work?
HEPA | ASHRAE | ULPA filters capture particulates using four main mechanisms: sieving, inertial impaction, interception, and diffusion. The filtration mechanism depends on the particle size and behavior.
A. Sieving
Sieving refers to the trapping of large particles that are too big to pass through the spaces between the filter fibers. While sieving is not the primary filtration method in HEPA filters, it still helps remove larger particles.
B. Inertial Impaction
This occurs when larger particles cannot adjust quickly to the changing airflow direction and continue in a straight path due to inertia, colliding directly with filter fibers. Heavier particles are more likely to experience inertial impaction.
C. Interception
Interception happens when particles following airflow paths come within one particle radius of a fiber and get captured by it, thus removing them from the airstream.
D. Diffusion
Diffusion involves smaller particles taking a zigzag or random path and eventually sticking to filter fibers. This is explained by Brownian motion, where gas molecules constantly collide in a random motion. Diffusion primarily affects particles smaller than 0.1 microns.
Filter efficiency is calculated by measuring the number of particles upstream and downstream of the filter. The downstream count is divided by the upstream count, subtracted from one, and multiplied by 100 to yield the efficiency percentage.
A Closer Look at HEPA Filters
HEPA and ULPA filters consist of fine interlaced fibers housed within a frame. These fibers, known as filter media, are usually made of fiberglass and have diameters ranging from 0.5 to 2.0 microns. Key factors affecting performance include fiber diameter, filter thickness, and face velocity.
To illustrate the size of particles captured, one micron equals one-millionth of a meter. Human eyes cannot see particles smaller than 40 microns.
- Hair: 100–150 microns
- Emissions: 1–150 microns
- Dust: <100 microns
- Pollen: 10–100 microns
- Spores: 3–40 microns
- Mold: 3–12 microns
- Bacteria: 0.3–60 microns
- Pure oxygen molecule: 0.005 microns
HEPA Filter Specifications
According to U.S. Department of Energy (DOE) standards widely adopted in American industry, a high-efficiency air filter must minimize airflow resistance or pressure drop—typically specified at 300 Pascals (0.044 psi).
European standards (EN 1822-1:2009) define HEPA categories based on the retention of the Most Penetrating Particle Size (MPPS).
According to GMP, filters must be leak-free. This is verified by qualification and routine leak tests, in accordance with ISO 14644-3. Best practices for the structure, performance, labeling, and certification of HEPA filters are maintained by the Institute of Environmental Sciences and Technology (IEST) and Underwriters Laboratories (UL).
Key requirements include:
- IEST-RP-C021: Testing of HEPA and ULPA media
- IEST-RP-CC001: HEPA and ULPA filters — structure and labeling requirements
- IEST-RP-CC034: Leak testing methods for HEPA and ULPA filters
- UL900: Certification and flammability compliance
- MIL-STD-282: U.S. military standard for air filter performance
Additional testing standards:
- ISO 14644-3: Leak testing during filter installation
- ISO 29463 (2017): High-efficiency filters and media for particle removal from air
- ISO 16890 (2017): General ventilation air filters
- PIC/S PI 032-2 GMP: Guide for Good Manufacturing Practice
- EN1822: Commonly used by air filter manufacturers for HEPA/ULPA filter classification
About E-FILT: Your Trusted Air Filter Manufacturer
E-FILT is a professional air filter manufacturer dedicated to providing advanced clean air solutions for industries ranging from pharmaceuticals to electronics and aerospace. With a commitment to quality, innovation, and compliance with international standards such as ISO 16890, EN1822, and ISO 14644, E-FILT delivers high-efficiency air filters that meet the stringent demands of modern cleanrooms. Whether you need HEPA, ULPA, or custom-designed filtration solutions, E-FILT ensures exceptional performance, reliability, and clean air where it matters most.