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ISO 29463-5:2022 — High-Efficiency Filters and Filter Media — Test Method for Filter Elements
Comprehensive guide to MPPS-based efficiency testing for HEPA and ULPA filters
Introduction to ISO 29463-5 and the MPPS Concept
ISO 29463-5:2022 specifies the reference test method for determining the efficiency of high-efficiency particulate air (HEPA) and ultra-low penetration air (ULPA) filter elements based on the Most Penetrating Particle Size (MPPS) principle. Derived from the EN 1822 series with extensive modifications for international adoption, this standard establishes a particle-counting methodology that covers filter efficiencies from 95 % up to 99.999 995 %.
The MPPS for micro-glass filter media typically lies in the 0.12 µm to 0.25 µm range — this is where mechanical filters are least efficient and therefore the most challenging particle size to capture.
The standard introduces three distinct efficiency test paths depending on filter group classification: a reference method using monodisperse or polydisperse aerosols, an alternate scan-test method for group H and U filters, and a statistical method for lower-efficiency group E filters. This tiered approach balances testing rigour with practical throughput in manufacturing environments.
| Filter Group | Efficiency Range | Test Method | Typical Application |
|---|---|---|---|
| ISO 15 E – ISO 25 E (EPA) | 95 % – 99.95 % | Statistical — MPPS particle counting | Hospital ventilation, cleanrooms ISO 8–9 |
| ISO 35 H – ISO 45 H (HEPA) | 99.95 % – 99.995 % | Reference — monodisperse or polydisperse aerosol | Pharmaceutical sterile zones, ISO 5 cleanrooms |
| ISO 50 U – ISO 75 U (ULPA) | 99.9995 % – 99.999995 % | Reference + optional scan test | Semiconductor fabs, nanotechnology labs |
The shift from mass-based efficiency measurement (the old DOP/PAO oil mist method) to particle-counting at MPPS gives up to 1000× greater sensitivity, enabling reliable classification of true ULPA-grade filters.
Test Apparatus and Aerosol Generation
The test duct system must include an air conditioning section, flow measurement, aerosol mixing section, and a filter mounting assembly with upstream and downstream sampling ports. Two aerosol types are permitted: monodisperse (geometric standard deviation σg < 1.15) using a generator such as the Electrostatic Classification Aerosol Generator, or polydisperse (σg > 1.5) using a liquid aerosol generator with DEHS or DOP.
For filters with charged media (electret filters), Annex C prescribes a conditioning and testing protocol that accounts for potential efficiency degradation over time due to discharge mechanisms. This is critical for applications where filter performance must remain stable throughout the service life.
Engineering Design Insights
From a practical design perspective, several factors directly influence test outcome validity:
- Aerosol neutralisation: The test aerosol must be brought to Boltzmann charge equilibrium to avoid electrostatic artefacts in particle counting.
- Sampling isokinetics: Upstream and downstream sampling must be isokinetic to prevent particle size bias — particularly important for particles above 0.5 µm.
- Coincidence error management: At high particle concentrations, the optical particle counter may undercount; dilution systems or concentration limits must be applied.
- Pressure drop stabilisation: A flushing period of at least 30 minutes at rated flow is required before efficiency measurement to allow the filter medium to reach equilibrium.
For membrane medium filters, the MPPS can shift below 0.1 µm, requiring specialised condensation particle counters (CPCs) rather than conventional optical particle counters (OPCs).
Data Evaluation and Reporting
The overall efficiency is determined by integrating local penetration measurements across the filter face. For group H and U filters, a scanning probe traverses the entire filter face with a defined overlap pattern to detect localised leaks. Any point where local penetration exceeds the class limit by more than 5× constitutes a failure.
The test report must document: reference to ISO 29463-5:2022, filter identification, test aerosol type and concentration, volume flow rate, pressure drop, MPPS, overall efficiency, and any local leak values. This level of documentation is essential for traceability in regulated industries such as nuclear and pharmaceutical manufacturing.
Frequently Asked Questions
Q: What is the difference between MPPS and the old DOP test?
A: MPPS (Most Penetrating Particle Size) identifies the particle diameter at which the filter has minimum efficiency — typically 0.12–0.25 µm for glass fibre media. The DOP test used a fixed 0.3 µm challenge and measured total mass penetration, which is far less sensitive and cannot correctly classify modern ULPA filters.
A: MPPS (Most Penetrating Particle Size) identifies the particle diameter at which the filter has minimum efficiency — typically 0.12–0.25 µm for glass fibre media. The DOP test used a fixed 0.3 µm challenge and measured total mass penetration, which is far less sensitive and cannot correctly classify modern ULPA filters.
Q: Can ISO 29463-5 be used for electret (charged) filter media?
A: Yes — Annex C provides specific procedures for charged media testing, including conditioning protocols to account for potential charge decay over the filter’s service life. However, the standard notes that no equivalent test procedure is universally prescribed.
A: Yes — Annex C provides specific procedures for charged media testing, including conditioning protocols to account for potential charge decay over the filter’s service life. However, the standard notes that no equivalent test procedure is universally prescribed.
Q: How does the scan test differ from the overall efficiency test?
A: The scan test (Annex A) uses a moving probe to measure local penetration across the entire filter face, detecting pinhole leaks or media defects. The overall efficiency test measures bulk penetration averaged over the whole filter element. Both are required for group H and U classification.
A: The scan test (Annex A) uses a moving probe to measure local penetration across the entire filter face, detecting pinhole leaks or media defects. The overall efficiency test measures bulk penetration averaged over the whole filter element. Both are required for group H and U classification.
Q: What are the key changes from the 2011 edition?
A: Normative references were updated, Annex C on charged fibre media was technically revised, and alignment with newer editions of related ISO 29463 parts was improved. The second edition (2022) supersedes ISO 29463-5:2011.
A: Normative references were updated, Annex C on charged fibre media was technically revised, and alignment with newer editions of related ISO 29463 parts was improved. The second edition (2022) supersedes ISO 29463-5:2011.
