Start with the claim, not the acronym
- HEPA and ULPA filters
- HEPA and ULPA are terms for high-efficiency particulate filters, and each should be tied to a named test method or classification framework. EPA describes a HEPA filter as a pleated mechanical air filter and cites the Department of Energy definition of high efficiency particulate air. IEST-RP-CC001 covers HEPA and ULPA filter units and provides a basis for customer-supplier agreement.1,3
In many U.S. indoor-air discussions, HEPA is shorthand for removing at least 99.97 percent of particles at 0.3 micrometer, with that size used as a worst-case MPPS reference. This does not make every high-efficiency filter a HEPA filter. The label alone also does not show whether a ULPA-class element, installed device, cleanroom module, or semiconductor tool interface was tested under the appropriate standard and flow condition.1,2,3
ULPA comparisons need to be method-specific. ISO 29463-1 classifies high-efficiency filters using performance determined through the ISO 29463 test series, including methods for filter media, leakage, and filter elements. The practical question is not simply HEPA versus ULPA, but which standard, filter format, airflow, particle counter, and acceptance endpoint apply to the project.4,5,6
| Question | Why it matters | Evidence to request |
|---|---|---|
| Is the claim HEPA, ULPA, or cleanroom cleanliness? | Each frame can point to a different standard, sample path, and report language. | Named standard, filter class target, tested configuration, and pass-fail endpoint |
| Is the sample media, an element, or a device? | Flat media, framed filters, installed modules, and ducted systems can have different bypass and seal risks. | Fixture drawing, seal approach, airflow, pressure drop, and upstream/downstream sampling plan |
| Does the claim include particles below 100 nm? | Nanoparticle behavior can sit outside ordinary cleanroom classification and MERV-style particle bands. | Added 5 to 100 nm detection plan, instrument range, dilution, background, and counting statistics |
| Will the result support certification language? | A laboratory test report is not automatically a product listing or certification. | Clear report wording separating test evidence, standards alignment, deviations, and certification limits |
MPPS is the method anchor
High-efficiency filter testing usually starts with MPPS, the most penetrating particle size. ISO 29463-5 specifies methods for determining filter efficiency at MPPS and includes guidance for filters with an MPPS less than 0.1 micrometer. For ULPA-class work, that can make nanometer-scale measurement planning important.1,6
ISO 29463-2 also matters because high-efficiency filter testing depends on aerosol production, measuring equipment, and particle-counting statistics. Low downstream counts make reporting detail especially important. The report should document background control, challenge stability, counter range, sample timing, and how low-count uncertainty was handled.5,9
- Use an ISO 29463 or EN 1822 frame when the claim is high-efficiency filter classification, MPPS penetration, or HEPA/ULPA element evidence.4,6
- Use paired upstream and downstream particle measurements to calculate penetration or efficiency under the stated flow and fixture condition.5,9
- Record pressure drop beside efficiency because a lower-penetration filter can also create a higher airflow resistance in the tested configuration.4,9
- Document deviations when a purifier, duct module, wafer-tool filter, or nonstandard housing cannot be represented as a standard filter element.3,4,9
Where 5 to 100 nm detection fits
A 5 to 100 nm endpoint should be treated as a nanoparticle detection extension, not a replacement for the named HEPA or ULPA standard. ARE Labs can measure particle-size distributions using fast mobility sizing in the nanometer range. The filtration efficiency service uses upstream and downstream CPC or OPC measurements and includes pressure-drop reporting.9,10
This extension is most useful when the claim, process risk, or customer specification depends on particles below 0.1 micrometer. ISO 29463-5 includes testing and classification guidance for filters with an MPPS below 0.1 micrometer. ISO 14644-1, however, states that its cleanroom particle-concentration classification range does not cover ultrafine particles below 0.1 micrometer.6,7,10
| Use case | Method concern | Added evidence |
|---|---|---|
| ULPA element or media development | MPPS or penetration may sit in the nanometer-scale region for the tested media. | 5 to 100 nm particle-size window, upstream/downstream counts, and penetration by size |
| Cleanroom supply module or fan-filter unit | Installed seals, bypass, and flow distribution can differ from media-only performance. | Fixture-specific filtration efficiency, pressure drop, and optional nanometer-scale downstream detection |
| Semiconductor wafer manufacturing support | Sub-100 nm particles can matter to process-control decisions even when ordinary cleanroom classification is reported separately. | Nanoparticle concentration trend, background subtraction, device state, and particle-size distribution |
| Air-treatment device with a high-efficiency filter | Fan speed, housing leakage, and re-entrainment can change installed performance. | System-level upstream/downstream measurements plus device particle emissions context when needed |
Cleanroom and semiconductor context
Cleanroom work adds a second layer of evidence. ISO 14644-1 classifies air cleanliness in cleanrooms and clean zones by airborne particle concentration, using threshold particle sizes from 0.1 micrometer to 5 micrometers. Particles below 0.1 micrometer fall outside that classification range.7
ISO 14644-3 provides test methods for cleanroom and clean-zone performance parameters, with procedures that vary by room type and occupancy state. Cleanroom classification and filter testing are therefore related but separate activities. Cleanroom classification measures air cleanliness in the controlled environment; filter testing evaluates a filter, media, or device path under defined conditions.4,7,8
- For cleanroom classification, define the room or clean zone, occupancy state, particle-size thresholds, sampling locations, and ISO 14644 reporting basis.7,8
- For a HEPA or ULPA filter element, define the sample, seal, flow, aerosol challenge, MPPS or size range, and pressure-drop endpoint.4,5,9
- For semiconductor or wafer-tool questions, decide whether the result needs a sub-100 nm particle count, a filter penetration curve, a cleanroom particle map, or a device-emissions check.7,9,10
- For installed air-treatment devices, separate media capture from housing bypass and particles introduced by fans, motors, ionizers, or process-air interactions.9,10
How to scope the test path
A practical HEPA versus ULPA study begins with the decision the report needs to support. A product team may need a media comparison, supplier qualification, filter-element MPPS penetration data, cleanroom troubleshooting, installed device performance, or a semiconductor contamination-control screen. That decision determines the fixture, aerosol, instrument set, replicate plan, and report language.3,4,5,6,9,10
- Send the filter format, dimensions, media type, gasket or seal design, intended airflow, target standard, and claim language before the method is selected.3,4,9
- State whether the endpoint is overall efficiency, penetration by size, local leak context, pressure drop, cleanroom particle classification, or 5 to 100 nm nanoparticle behavior.4,6,7,10
- Choose counters and dilution around the expected concentration range because low downstream particle counts require attention to background and counting statistics.5,9
- Decide in advance whether the report should avoid certification wording and instead present standards-aligned evidence, deviations, and method limits.3,4,9