Start with the claim, not the acronym
- HEPA and ULPA filters
- HEPA and ULPA are high-efficiency particulate filter terms that should be tied to a named method or classification frame. EPA describes HEPA 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 as a basis for customer-supplier agreement.1,3
For many U.S. indoor-air discussions, HEPA shorthand means at least 99.97 percent removal of particles at 0.3 micrometer, with that size treated as a worst-case MPPS reference. That does not make every high-efficiency filter a HEPA filter, and it does not answer whether a ULPA-class element, installed device, cleanroom module, or semiconductor tool interface has been tested under the right standard and flow condition.1,2,3
ULPA discussions should be more method-specific. ISO 29463-1 establishes high-efficiency filter classification based on performance determined through the ISO 29463 test series, including filter-media, leakage, and filter-element methods. The useful comparison is therefore not only HEPA versus ULPA, but which standard, filter format, airflow, particle counter, and acceptance endpoint are being used.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
The high-efficiency filter question 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, which is why nanometer-scale measurement planning can matter for ULPA-class work.1,6
ISO 29463-2 is also relevant because high-efficiency filter testing depends on aerosol production, measuring equipment, and particle-counting statistics. When downstream counts are low, the report needs to show 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 scoped as a nanoparticle detection extension, not as a replacement for the named HEPA or ULPA standard. ARE Labs' particle-size distribution capabilities include fast mobility sizing in the nanometer range, while the filtration efficiency service uses upstream and downstream CPC or OPC measurements with 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 explicitly recognizes testing and classification guidance for filters with an MPPS below 0.1 micrometer, and ISO 14644-1 states that cleanroom classification does not cover ultrafine particles below 0.1 micrometer in its particle-concentration classification range.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 evidence layer. ISO 14644-1 classifies air cleanliness by airborne particle concentration in cleanrooms and clean zones, using threshold particle sizes from 0.1 micrometer to 5 micrometers for classification. It also states that particles below 0.1 micrometer are outside that classification range.7
ISO 14644-3 provides cleanroom and clean-zone test methods for performance parameters and distinguishes test procedures by room type and occupancy state. That makes cleanroom classification and filter testing related but separate work: one evaluates air cleanliness in the controlled environment, while the other 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 starts with the decision the report must support. Product teams may need media comparison, supplier qualification, filter-element MPPS penetration, cleanroom troubleshooting, installed device performance, or a semiconductor contamination-control screen. Each path changes 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