In the pursuit of clean air, HEPA and ULPA filters are hailed as the crown jewels. However, for a long time, different standards existed in the global market for judging the authenticity and quality of these “jewels.” US standards, European standards, and national standards intertwined, leading to confusing performance claims and inconsistent product quality. This dispute was finally resolved with the emergence of ISO 29463—an international standard developed in Mainz, Germany, entitled “High-efficiency particulate air filters and ultra-high-efficiency filters for removing particulate matter from the air”—becoming a globally recognized, scientific, and rigorous unified standard.
I. Why Do HEPA and ULPA Filters Need a Unified Measurement Standard?
Before the advent of ISO 29463, the HEPA/ULPA field faced two major challenges:
- 1. Inconsistent testing methods: Some standards used the DOP method, while others used the sodium flame method. The efficiency values obtained from these methods could not be directly compared, creating significant obstacles to cross-border procurement and technical exchange.
- 2. Vague performance descriptions: The market was flooded with vague labels such as “99.9% HEPA,” without specifying the particle size or the testing method used. Many filters showed high efficiency for larger particles (e.g., 0.5 microns), but not necessarily for the most penetrating particle size, leading to misrepresentation of performance.
II. The Core Revolution of ISO 29463: MPPS Becomes the Sole Benchmark
The core contribution of ISO 29463 lies in its comprehensive adoption and internationalization of the essence of the European standard EN 1822—the Most Penetrating Particle Size (MPPS) method.
- What is MPPS? Theoretically, filters do not necessarily have higher removal efficiency for smaller diameter particles. Between 0.1 and 0.3 micrometers, there exists a particle size range that is the most difficult to filter because it simultaneously avoids both interception and diffusion, the two main capture mechanisms. This particle size is known as MPPS (Minimum Particulate Filter).
- Why is MPPS so important? A filter’s efficiency in filtering MPPS is its minimum efficiency, its performance “weakest link.” Ensuring efficient filtration of MPPS means higher or equal efficiency for all larger and smaller particles. This is like using the most rigorous exam to measure a student’s true ability.
III. A New Classification System: Clearly Defining HEPA and ULPA
ISO 29463 establishes a precise classification and coding system based on MPPS efficiency, completely ending the misuse of the term “HEPA .”
| Group | ISO Code | Minimum Efficiency (%) at MPPS | Corresponding Traditional Name |
| High-Efficiency Filter (EPA) | ISO 15 E | 85% | |
| ISO 20 E | 95% | ||
| ISO 25 E | 99.5% | ||
| HEPA Filter | ISO 30 H | 99.9% | H13 |
| ISO 35 H | 99.95% | H13/H14 | |
| ISO 40 H | 99.99% | H14 | |
| ULPA Filter | ISO 45 U | 99.995% | U15 |
| ISO 50 U | 99.9995% | U16 | |
| ISO 55 U | 99.99995% | U17 | |
| ISO 60 U | 99.999995% | U18 | |
| ISO 65 U | 99.9999995% | U19 | |
| ISO 70 U | 99.99999995% | U20 |
From then on, whether a filter is “true HEPA” or “quasi-ULPA” is no longer determined by marketing rhetoric, but by its explicit ISO code. For example, a filter labeled ISO 35 H immediately indicates that its efficiency at MPPS is guaranteed to be no less than 99.95%.
IV. More Comprehensive Quality Assessment by ISO 29463
Besides the core filtration efficiency, ISO 29463 also makes strict provisions for other aspects affecting filter performance and reliability:
- Resistance Test: Specifies the initial resistance at rated airflow.
- Dust Holding Capacity Test: Provides a scientific method for evaluating filter lifespan.
- Sealing Test: Ensures no leakage between the filter and the mounting frame. This is crucial because even the best filter element is useless if the frame leaks.
ISO 29463 is not just a technical document; it embodies a rigorous scientific spirit. It pulls HEPA and ULPA technologies back from the mire of “marketing concepts” to the solid ground of “hardcore technology,” establishing a clear and fair order for the entire industry through the scientific concept of Most Penetrating Particle Size (MPPS) and a globally unified grading system. Trenntech recommends looking for the ISO 29463 standard and its grading codes when choosing filtration products that concern health, process, and safety.