Cleanrooms enable the production of highly sensitive materials, requiring filtration of particles smaller than a micron, too fine for regular filters.
HEPA filters were designed specifically to trap these tiny contaminants, protecting critical cleanroom environments.
But how exactly do cleanroom HEPA filters work? Where should they be placed, and what specifications must they meet? This comprehensive guide answers these questions and more.
What Is a Cleanroom?
A cleanroom is a precisely engineered environment designed to maintain ultra-low levels of airborne particles, microbes, and chemical vapors.
Unlike ordinary rooms, cleanrooms follow strict protocols to control contamination through advanced air filtration, regulated airflow patterns, and rigorous operational procedures. These specialized spaces are indispensable in industries where microscopic pollutants could compromise product integrity, scientific research, or manufacturing precision.
The foundation of a cleanroom lies in its ability to filter and circulate air at controlled velocities while maintaining positive or negative pressure relative to surrounding areas.
Personnel must wear protective garments like coveralls, gloves, and face masks to minimize human-sourced contamination. Surfaces are constructed with non-shedding materials, and cleaning procedures are meticulously enforced.
Classifications of Cleanrooms
Cleanrooms are classified under the ISO 14644-1 standard, which defines permissible particle concentrations for different cleanliness levels.
An ISO Class 5 cleanroom, for instance, allows no more than 3,520 particles (≥0.5 microns) per cubic meter, making it 100 times cleaner than an ISO Class 8 environment.
Industries such as semiconductor fabrication, pharmaceutical manufacturing, and aerospace engineering rely on these controlled spaces to ensure defect-free production and sterile conditions. Here’s an overview of all classifications:
| ISO Class | ≥ 0.1 µm | ≥ 0.2 µm | ≥ 0.3 µm | ≥ 0.5 µm | ≥ 1 µm | ≥ 5 µm |
| ISO 1 | 10 | – | – | – | – | – |
| ISO 2 | 100 | 24 | 10 | – | – | – |
| ISO 3 | 1,000 | 237 | 102 | 35 | – | – |
| ISO 4 | 10,000 | 2,370 | 1,020 | 352 | 83 | – |
| ISO 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | 29 |
| ISO 6 | 1,000,000 | 237,000 | 102,000 | 35,200 | 8,320 | 293 |
| ISO 7 | – | – | – | 352,000 | 83,200 | 2,930 |
| ISO 8 | – | – | – | 3,520,000 | 832,000 | 29,300 |
| ISO 9 | – | – | – | 35,200,000 | 8,320,000 | 293,000 |
What Is a HEPA Filter?
A High-Efficiency Particulate Air (HEPA) filter is a critical component in maintaining cleanroom standards by trapping microscopic particles with exceptional efficiency.
True HEPA filters for clean rooms, as defined by U.S. DOE standards, must capture 99.97% of particles measuring 0.3 microns in diameter, the most challenging size to filter due to particle behavior in airflow.
How HEPA Filters Work
HEPA filters use a combination of three mechanisms to trap contaminants:
- Interception: Particles following the airstream collide with and adhere to filter fibers.
- Impaction: Larger particles cannot avoid fibers due to inertia and embed directly into them.
- Diffusion: Ultrafine particles (below 0.1 microns) move erratically (Brownian motion) and are intercepted by fibers.
What Is a HEPA Filter Made of?
HEPA filters are often made of aluminum or stainless steel to prevent air bypass. They are integral to laminar airflow systems (more on these systems in a moment), where filtered air moves uniformly to sweep contaminants away from critical zones.
Types of HEPA Filters
- Standard HEPA (H13): Filters 99.95–99.99% of 0.3-micron particles.
- ULPA (U15–U17): Ultra-Low Penetration Air filters capture 99.999% of particles down to 0.12 microns, used in stricter cleanrooms.
- Fire-Resistant HEPA: Designed for hazardous environments, with flame-retardant materials.
Role Of A HEPA Filter In A Cleanroom
Unlike standard HVAC filters, HEPA filters are engineered to meet stringent efficiency benchmarks, ensuring that even submicron particles are trapped.
Their placement and integration into cleanroom ventilation systems are meticulously designed to align with ISO classifications and industry-specific regulations, such as FDA cGMP for pharmaceuticals or IEST standards for microelectronics.
How HEPA Filters Maintain Cleanroom Standards
HEPA filters uphold cleanroom standards through three core mechanisms:
- Mechanical Filtration Efficiency
- Governed by EN 1822 and IEST RP-CC001, HEPA filters (H13–H14) must retain ≥99.95% of 0.3-micron particles. ULPA filters (U15–U17) extend this to 99.999% at 0.12 microns.
- Particle capture relies on diffusion (for <0.1 µm), interception (0.1–0.4 µm), and impaction (>0.4 µm).
- Air Exchange Rate Control
- Cleanrooms require 20–600 air changes per hour (ACH), depending on ISO class. HEPA filters enable this by balancing high flow rates with minimal pressure drop (typically <250 Pa for new filters).
- Containment and Airflow Design
- Sealed housings (per ISO 14644-3 leak-test protocols) prevent bypass leakage.
- Scan testing with DOP/PAO aerosols verifies integrity post-installation.
For ISO Class 5 cleanrooms, HEPA-filtered laminar airflow achieves ≤3,520 particles/m³ (≥0.5 µm), while ISO Class 8 permits 3,520,000 particles/m³—demonstrating the filter’s pivotal role in classification compliance.
Cleanroom Class Requirements and HEPA Usage
Cleanroom ISO classes dictate HEPA filters specifications and deployment strategies:
| ISO Class | Max Particles/m³ (≥ 0.5 µm) | HEPA Filter Usage |
| ISO 3 | ≤1,000 | ULPA filters (U15+) in unidirectional airflow |
| ISO 5 | ≤3,520 | HEPA (H13-H14) in ceiling grids or FFUs |
| ISO 7 | ≤352,000 | HEPA in HVAC supply + terminal filtration |
| ISO 8 | ≤3,520,000 | HEPA in central air handlers |
Key Considerations
- Pharmaceutical ISO 5 zones often use terminal HEPA filters near air supply diffusers to avoid duct contamination.
- Semiconductor ISO 4–5 cleanrooms deploy fan filter units (FFUs) with redundant HEPA arrays for fault tolerance.
Where To Place A HEPA Filter
HEPA filter placement is determined by cleanroom design and airflow strategy:
- Ceiling-Mounted (Laminar Flow Cleanrooms)
- Filters cover 80–100% of the ceiling to create downward unidirectional airflow (common in ISO 3–5). Examples: Sterile fill lines, wafer fabrication.
- Fan Filter Units (FFUs)
- Modular HEPA filters with integrated blowers, used in softwall cleanrooms or retrofits.
- HVAC Supply Ducts (Turbulent Flow Cleanrooms)
- HEPA filters are installed downstream of cooling coils and pre-filters (typical in ISO 7–8).
- Wall-Mounted Recirculation Units
- For localized contamination control in ISO 6–8 zones (e.g., packaging areas).
Important note: Filters must be accessible for testing and replacement without disrupting cleanroom operations.
Laminar Vs Turbulent Airflow
Cleanrooms employ two primary airflow strategies, each with distinct advantages:
Laminar (Unidirectional) Airflow
This airflow creates parallel streamlines moving at a consistent velocity (typically 0.45 m/s ±20%). This configuration provides the most effective particulate control and is essential for ISO Class 3-5 cleanrooms.
The uniform airflow pattern sweeps particles away from critical zones, making it ideal for applications like sterile compounding or microchip fabrication.
Turbulent (Non-unidirectional) Airflow
This one relies on mixing and dilution to control contamination. While less effective per unit of air volume, turbulent systems are more energy-efficient and cost-effective for ISO Class 6-8 cleanrooms.
These systems require careful placement of HEPA filters and higher air exchange rates (20-40 ACH) to maintain cleanliness levels. Common applications include medical device packaging and some pharmaceutical secondary processing areas.
Choosing the Right HEPA Filter for Your Cleanroom
Selecting the optimal HEPA filter requires balancing efficiency, airflow requirements, and cleanroom classification.
Key considerations include filter grade (H13-H14 for most cleanrooms), frame material (aluminum for standard use, stainless steel for corrosive environments), and compatibility with existing HVAC or FFU systems.
The filter’s pressure drop (typically 200-250 Pa when new) directly impacts energy costs, making low-resistance designs preferable for high-flow applications.
Factors To Consider
- Particle Load: Higher contamination environments may require more frequent replacements
- Airflow Velocity: Must match cleanroom ACH requirements without excessive pressure drop
- Chemical Resistance: Critical for labs handling solvents or aggressive vapors
- Lifespan: Typically 5-10 years, but it depends on usage and pre-filtration
Filter Testing and Certification
All HEPA filters should comply with EN 1822 or IEST-RP-CC001 standards. Routine DOP/PAO testing verifies integrity, while MPPS (Most Penetrating Particle Size) testing confirms efficiency at 0.3 microns.
Certifications from NSF, ISO, or FDA may be required for regulated industries. Annual testing is recommended, with more frequent checks in critical applications.
FAQs
How Long Do Cleanroom Hepa Filters Last?
Lifespan varies (1-5 years) based on usage, contamination, and pre-filtration. Regular checks and pressure drop monitoring are crucial; replace when performance declines or fails leak tests (6-12 months).
What Is the Specification of a Clean Room HEPA filter?
HEPA filters must remove at least 99.97% of particles ≥0.3 microns. Pressure drop is typically around 300 Pascals at the nominal flow rate. Standards like EN 1822 define efficiency classes (H13, H14).
What’s the Difference Between Hepa and Ulpa Filters?
HEPA filters capture 99.97% of ≥0.3 µm particles. ULPA filters capture 99.999% of ≥0.12 µm particles, offering higher efficiency but with greater pressure drop and cost. Read our recent blog for a deeper dive into the differences.
How Do I Know if My Cleanroom Hepa Filter Is Still Effective?
Regular integrity (leak) testing using aerosol photometry is key. Monitor pressure drop; a significant increase indicates loading. Particle counting upstream and downstream assesses filtration efficiency.
What’s the Typical Pressure Drop for a HEPA Filter?
The initial pressure drop for a clean HEPA filter is typically around 25 mm of water column (250 Pa). Replacement is often economical when the pressure drop doubles to 50 mm WC (500 Pa).