Leak detection of high-efficiency filters (HEPA/ULPA) is a critical part of cleanroom validation.
With the implementation of GMP standards, especially in pharmaceutical industries, HEPA filter leak testing has become a mandatory inspection requirement.
Today, industries such as pharmaceuticals, hospitals, electronics, food, and cosmetics all require reliable HEPA filter integrity testing to ensure cleanroom performance.
Below are five common HEPA filter leak detection methods used in practice.
1. Sodium Flame Method
The sodium flame method uses sodium chloride (NaCl) aerosol as the test challenge.
The aerosol is generated by atomizing a salt solution using compressed air. After drying, fine salt particles enter the air duct. Air samples are taken upstream and downstream of the filter and introduced into a hydrogen flame.
The presence of sodium causes the flame to change color and brightness, which is used to estimate particle concentration and filter efficiency.
Limitations:
- Low sensitivity
- Not suitable for HEPA/ULPA filters
- Rarely used in modern testing systems
2. Oil Mist Method
The oil mist method uses oil aerosols (typically paraffin oil) with particle sizes around 0.3–0.5 μm.
Filter performance is evaluated by comparing the turbidity (opacity) of air upstream and downstream of the filter.
Limitations:
- May contaminate or damage filters
- Results are not directly readable
- Time-consuming
3. DOP Method (Traditional Standard Method)
The DOP method has historically been one of the most widely used methods for HEPA filter testing.
It uses dioctyl phthalate (DOP) aerosol particles with a size of approximately 0.3 μm. The aerosol is generated by heating DOP liquid, forming vapor that condenses into fine droplets.
Filter efficiency is determined by measuring aerosol concentration before and after the filter.
Notes:
- Now often replaced by safer alternatives (e.g., PAO)
- Still referenced in older standards and practices
4. Fluorescence Method
This method uses sodium fluorescein particles generated by a sprayer.
Air samples are collected before and after the filter, and the particles are dissolved in water. The fluorescence intensity of the solution is measured to determine particle concentration and filtration efficiency.
Limitations:
- Complex process
- Requires laboratory analysis
- Not suitable for real-time leak detection
5. Particle Counting Method (Scanning Method)
The particle counting method is currently the most widely used and internationally accepted method for HEPA filter leak detection.
It complies with standards such as:
- EN 1822
- ISO 29463
How it works
- Aerosol (e.g., DEHS or PAO) is introduced upstream
- A particle counter measures particle concentration
- The entire filter surface is scanned point by point
- Local leaks are detected based on particle concentration differences
Advantages
- High sensitivity
- Real-time detection
- Accurate leak localization
- Suitable for HEPA and ULPA filters
Recommended Solution: Automatic HEPA Filter Scanning Test Bench
For modern HEPA filter manufacturers and cleanroom applications, the particle counting scanning method is the most reliable solution.
Equipment such as the SC-L8023 HEPA filter leak test bench is designed for:
- Automatic scanning of the full filter surface
- High-sensitivity leak detection
- Stable aerosol generation
- Compliance with EN 1822 and ISO 29463
The system uses a high-precision particle counter and scanning mechanism to ensure consistent and repeatable testing results, making it ideal for production lines and quality control laboratories.
Conclusion
Among the five methods, traditional techniques such as sodium flame, oil mist, and fluorescence methods are gradually being replaced.
Today, the particle counting scanning method has become the industry standard due to its accuracy, efficiency, and compliance with international standards.
For manufacturers aiming to meet strict quality requirements, investing in an automatic HEPA filter leak test system is essential.
