Understanding ISO 29463 – HEPA and ULPA Filter Standards

Overview of ISO 29463 — Global Filter Standard

As the international standard for high-efficiency particulate air (HEPA) and ultra-low penetration air (ULNA) filters, ISO 29463 provides a universal framework for their classification, testing, and marking.

This standard was developed to replace a complex patchwork of national and regional standards that had created significant compliance burdens and uncertainty, offering instead a single, harmonized set of criteria for manufacturers and end-users.

ISO 29463-1 details a filter classification system based on efficiency, which is measured against test procedures from other parts of the standard (ISO 29463-3, -4, and -5).

HEPA and ULNA Filters — Classification Explained

ISO 29463 classifies filters into 13 distinct groups, from ISO 15 E to ISO 75 U, based on efficiency levels that range from 95% to 99.999995%. These classes are organized into three main categories:

• EPA (Efficient Particulate Air)

• HEPA (High-Efficiency Particulate Air): Covers classes ISO 35 H to ISO 45 H, essential for demanding environments.

• ULNA (Ultra-Low Penetration Air): Includes classes ISO 50 U to ISO 75 U for environments requiring maximum air purity.

This entire classification system is based on a filter’s efficiency at its Most Penetrating Particle Size (MPPS)—the particle size it finds most difficult to capture.

Testing Procedures for Filter Efficiency

To ensure each filter meets its classification, ISO 29463 outlines standardized testing procedures that use the Most Penetrating Particle Size (MPPS) as the benchmark. This approach guarantees reliable protection across the entire particle spectrum.

The testing process involves challenging the filter with a controlled liquid (e.g., DENS, PAO oil) or solid aerosol.

To ensure complete filter integrity, the standard mandates several distinct evaluations:

• Integral Efficiency: Measures the overall performance of the entire filter.

• Local Efficiency: Scans the filter face to detect potential inconsistencies or flaws.

• Leakage Tests: Verifies that no unfiltered air bypasses the filter media through seals or frame defects.

This comprehensive testing regimen ensures that certified filters are not only highly efficient but also structurally sound.

Understanding MPPS — Most Penetrating Particle Size

The Most Penetrating Particle Size (MPPS) is a fundamental concept in ISO 29463. It refers not to the smallest particle, but to the specific size that is most difficult for a filter to capture.

The existence of an MPPS is a direct result of the physics of filtration. Tiny particles (<0.1 μm) are captured by diffusion, while larger ones (>0.4 μm) are stopped by impaction and interception.

This principle of evaluating filters at their MPPS was a key principle of the preceding European EN 1822 standard and remains the fundamental criterion in ISO 29463. This methodology provides a reliable basis for classification, guaranteeing that a filter’s rated efficiency (e.g., 99.97%) truly reflects its minimum performance.

Leakage Testing — Ensuring Filter Integrity

Filter media efficiency alone is insufficient; the integrity of the entire filter assembly is critical. Because microscopic leaks in the filter pack, sealant, or frame can allow contaminants to bypass the media, ISO 29463 mandates leakage testing to verify the structural integrity of the complete unit.

Leakage tests are performed at the filter’s MPPS to test it under the most challenging conditions. ISO 29463 outlines several methods for this, including:

• Photometer Scanning: Employs polydisperse aerosols to scan the filter face and detect localized leaks.

• Oil Thread Test: Directs a fine stream of aerosol along seals and the frame to visually identify leakage.

• Other Validated Methods: The standard allows for the use of other proven techniques, accommodating future technological advancements.

The goal is to confirm uniform, leak-free performance, ensuring that pinholes, gasket imperfections, or frame damage cannot compromise the filter’s efficiency rating.

Materials Used in Filter Media

The performance of HEPA and ULNA filters is determined by their media composition. This intricate fiber matrix is engineered for precise contaminant capture, with microglass and advanced synthetic fibers being the most common materials. A filter’s final classification under ISO 29463 is directly linked to this material choice.

The two primary types of filter media are:

• Microglass Fiber: The traditional standard, consisting of fine glass filaments pressed into a sheet. It captures particles through mechanical means (impaction, interception, and diffusion).

• Charged Synthetic Fibers (Electret Media): These materials are electrostatically charged to attract and hold particles. This electrostatic charge enhances efficiency, especially for small particles, often with lower air resistance.

ISO 29463–5:2022 — Key Specifications

ISO 29463-5:2022 details the practical testing methodology for determining the efficiency of HEPA and ULNA filters. It provides the precise methods for evaluation, ensuring that any filter claiming a classification has been tested against consistent, internationally recognized procedures.

ISO 29463-5:2022 is the key standard for compliance and verification. It provides manufacturers with clear guidelines to validate their products and gives end-users confidence that a filter will perform as advertised. By harmonizing testing protocols globally, the standard eliminates ambiguity and ensures a filter’s classification is both consistent and reliable, regardless of where it is used.