Comprehensive Overview of HEPA, ULPA, and High-Temperature Air Filters
Air filtration systems in pharmaceutical manufacturing are organized in a sequential, multi-stage process. Each stage plays a crucial role, collectively ensuring that the air supplied to cleanrooms meets strict cleanliness standards. Below is a detailed overview of commonly used air filters in pharmaceutical facilities:
01. Pre-Filter (Primary Filter)
Position: Serves as the initial stage or pre-filter in the purification system.
Function: Captures larger particles with diameters ≥10μm, such as dust, pollen, insects, and fibers. Its main role is to protect subsequent medium- and high-efficiency filters from rapid clogging, thereby extending their lifespan and reducing operational costs.
Structure: The most common design is panel type, but pleated and bag-type (pre-filter bags) structures are also used. Filter media are typically synthetic fiber or non-woven fabric.
Replacement Cycle: Usually 1-3 months, depending on ambient air quality.
02. Medium-Efficiency Filter
Position: Intermediate filtration stage, located after the pre-filter and before the high-efficiency filter.
Function: Captures particles between 1μm and 10μm, reducing the load on high-efficiency filters. This step is essential to improve overall filtration efficiency and prolong the lifespan of HEPA filters.
Structure: Commonly bag-type design, offering higher dust-holding capacity and lower resistance. Panel and pleated types are also available.
Replacement Cycle: Typically 6-12 months.
03. High-Efficiency Filter (HEPA)
Position: Terminal filtration stage, crucial for achieving cleanroom air standards.
Function: Filters particles ≥0.3μm (or 0.5μm) with efficiencies between 99.97% and 99.995% (for 0.3μm particles). Effectively removes bacteria, virus carriers, and other contaminants, meeting Class A or B cleanroom requirements.
Structure: Made of glass fiber media with frames in wood, aluminum, or stainless steel. The structure must be completely sealed to prevent leaks.
Installation and Replacement: Installed at the air supply terminal. Leakage testing (DOP/PAO test) is required to ensure proper sealing. HEPA filters cannot be washed; replacement is mandatory. Typical service life is 2-5 years.
04. Ultra-Low Penetration Air Filter (ULPA)
Position: Terminal filter for environments with extremely high cleanliness requirements.
Function: Filters particles ≥0.12μm with efficiency ≥99.9995%, suitable for specialized cleanrooms, high-level biosafety labs, or research areas.
Application: Less common in standard pharmaceutical production, but used in specific high-precision processes requiring cleaner-than-Class A air.
05. High-Temperature HEPA Filter
Position: Terminal filter for high-temperature environments.
Function: Used in sterilization ovens, dry-heat cabinets, and high-temperature tunnel ovens where temperatures reach 140°C–350°C to eliminate bacteria and pyrogens (e.g., in injectable water production). Standard HEPA media and sealants cannot withstand such heat, requiring filters with heat-resistant glass fiber media, stainless steel frames, and high-temperature sealants.
Feature: Maintains filtration efficiency and structural integrity under extreme temperatures.
Summary and Selection Guidelines
Selecting air filters for pharmaceutical facilities is a rigorous process, following GMP (Good Manufacturing Practice) standards. Decisions should consider cleanroom classification (A/B/C/D), specific processes, and airflow patterns.
| Filter Type | Main Function | Particle Size | Typical Efficiency | Common Installation |
|---|---|---|---|---|
| Pre-Filter | Protects downstream filters, pre-filtration | ≥10μm | 60-90% (by weight) | Air handling unit intake or initial section |
| Medium Filter | Protects HEPA, intermediate filtration | 1-10μm | 40-95% (F5-F9, photometric method) | After air handling unit fan, before cooling coils |
| HEPA | Terminal filtration, ensures cleanroom air | ≥0.3μm | 99.97-99.995% (H13-H14) | Cleanroom supply air terminal |
| ULPA | Ultra-high standard terminal filtration | ≥0.12μm | ≥99.9995% (U15-U17) | High-demand cleanroom supply air terminal |
| High-Temperature HEPA | Terminal filtration in high-temperature environments | ≥0.3μm | 99.97-99.995% | Sterilization ovens, tunnel ovens |
Choosing the right filter depends on the type of pharmaceutical product and the process requirements. Always align filter selection with practical workflow and cleanroom standards to ensure optimal air quality and compliance.
