Installed filtration

HEPA / ULPA Filter Integrity Testing

How installed-filter integrity testing works, and which technologies form the measurement chain from challenge aerosol through upstream reference and dilution to downstream scanning and documented evidence. The test looks for local leakage in the installed filter and its accessible sealing interfaces.

Discuss a filter-integrity requirement View the measurement architecture
Cleanroom corridor showing an installed terminal filter ceiling, sealed panel walls and airlock doors — the installed filter systems that an integrity test verifies
Installed terminal-filter ceiling — the complete installed system, not only the filter media, is what an integrity test verifies
Installed-filter test requirement

Installed filtration system leakage scope

An installed HEPA or ULPA filter can meet its factory efficiency specification and still allow local leakage once it is installed. The measurement looks for local leakage through the installed filter and the accessible perimeter, seal, frame and mounting interfaces, according to the applicable method and the installation itself. Paths that the scan cannot reach are outside what the measurement can show.

Upstream reference

Establish the challenge before evaluating leakage

The downstream count is meaningful only when it is evaluated against a known upstream aerosol concentration.

  • Challenge: sufficient concentration for sensitive leak detection.
  • Conditioning: a sampled upstream branch is diluted into the counter's working range.
  • Evidence: the reference and downstream scan are retained as one measurement record.

Topas cites VDI 2083 sheets 1–3 for an upstream concentration of at least 3.5 million particles/m³ in this particle-counter method.

Downstream sampling

Match probe geometry and inlet velocity to the airflow

Isokinetic sampling keeps the collected sample representative of the air leaving the installed filter face.

  • Probe form: rectangular geometry supports corners, seals and systematic face scanning.
  • Velocity: the probe inlet is matched to the local filter-face airflow.
  • Counter flow: the probe variant is selected for the particle counter used.

SYS 529: 28.3 L/min counter flow, 31–47 cm/s design range and 1:5.3 rectangular aspect ratio.

Governing references

ISO 14644-3Installed cleanroom and clean-zone performance test methods EN 1822-4Leakage scanning of high-efficiency filter elements as manufactured VDI 3491Test-aerosol preparation and dilution engineering context 

The installed system and the filter element are different test objects. ISO 14644-3 addresses the installed cleanroom; EN 1822 and ISO 29463 address the manufactured element and media.

Measurement architecture

Installed-filter integrity measurement architecture

The chain has a main airflow path and a separate sampling branch. Reading it as a single line misrepresents the physical arrangement — the dilution stage conditions a sampled branch, it does not sit in the main duct.

Measurement architecture showing an ATM 228 introducing a challenge aerosol into the supply air upstream of an installed HEPA or ULPA filter; a separate isokinetic sample branch taken off the upstream plenum passing through a DIL 544 or DIL 554 dilution system to a CPA 341 for upstream reference measurement; and on the downstream clean side a SYS 528 or SYS 529 rectangular scan probe feeding particle detection, with results evaluated and documented in CRQWin
The dilution stage conditions the sampled upstream branch only; it is not in the main duct path. Aerosol, acceptance criteria, scan technique and probe geometry follow the applicable test method and project specification.
  1. Stage 1

    Prepare the installation

    Confirm the airflow condition, accessible scan surfaces, permitted aerosol and applicable acceptance criterion.

  2. Stage 2

    Generate the challenge aerosol

    Produce a reproducible aerosol in the required size range and at the concentration specified by the test method.

  3. Stage 3

    Verify the upstream challenge

    Confirm adequate mixing across the filter face, dilute the sampled branch where required and establish the upstream reference concentration.

  4. Stage 4

    Scan the downstream face

    Traverse the filter face, perimeter, frame, seals and accessible housing interfaces using the specified probe geometry and scan technique.

  5. Stage 5

    Resolve and retest

    Record located leakage, complete permitted corrective work and repeat the affected scan area or full test as required.

  6. Stage 6

    Document the result

    Record the upstream reference, aerosol, scan technique, acceptance result and the operating conditions that produced it.

Measurement-chain configuration

Topas documents a cleanroom integrity-testing chain built from ATM 228 aerosol generation, DIL 544 or DIL 554 upstream concentration reduction and reference measurement, CPA 341 particle counting, SYS 529 downstream scanning and CRQWin evaluation.

Engineering considerations

Measurement-chain engineering requirements

Five functions have to operate as one measurement chain. Each has a defined input, equipment requirement and validity condition that affects the resulting evidence.

  1. Function 1

    Challenge generation

    Select a stable aerosol substance, size range and concentration appropriate to the method, filter system and site constraints.

  2. Function 2

    Reference and dilution

    Reduce the sampled upstream concentration into the counter range using a known dilution ratio and a flow matched to the counter.

  3. Function 3

    Particle measurement

    Use a counter with the required flow, counting efficiency and zero-count performance; ISO 21501-4 governs instrument performance.

  4. Function 4

    Downstream scanning

    Match the rectangular isokinetic probe to the counter flow and maintain the inlet velocity required by the applicable scan method.

  5. Function 5

    Evaluation and documentation

    Evaluate downstream counts against the upstream reference and retain the scan path, conditions, results and applicable acceptance criterion.

Standards

Standards and test-method applicability

These references are related but have different scopes. Interchanging them changes what a test result actually demonstrates.

Reference roles for installed-filter leakage measurement. Confirm the governing edition, acceptance criterion and national adoption in the approved test protocol.
ReferenceEdition / statusTechnical relevance
ISO 14644-3 2019 (Edition 2) — Current published reference Installed cleanroom / clean-zone performance-test context, including filter-system leakage methodology where applicable
ISO 29463-4 2011 — Current published reference Leakage of high-efficiency filter elements by scanning — the filter as manufactured, not as installed
EN 1822-4 2009 (legacy) — Referenced in manufacturer documentation Earlier scan method for element leakage, retained here only because Topas documentation cites it
ISO 21501-4 2018 (Edition 2) + Amendment 1:2023 — Current published reference Light-scattering airborne particle-counter performance and calibration context
VDI 3491 Current published reference Test-aerosol generation, preparation and dilution engineering context
VDI 2083 Current published reference Cleanroom engineering and testing context where applicable, including probe design and upstream challenge concentration guidance

Scroll the table horizontally →

Test-object scope

Installed cleanroom filter-integrity testing and factory filter-element testing are related but distinct test contexts. The applicable method and acceptance criteria depend on installation, filter type, project specification and governing standard.

EN 1822, ISO 29463 and ISO 14644-3 must not be used interchangeably. Their scopes overlap in subject but not in purpose: the EN ISO 29463 parts address leakage and efficiency of filter elements and media as manufactured, while ISO 14644-3 addresses performance testing of the installed cleanroom or clean zone.

Standards applicability
ISO 14644-3does not test the filter element as manufactured. It addresses the installed cleanroom or clean zone.
EN 1822-4 / ISO 29463-4do not automatically define installed cleanroom integrity testing. They address the element and media.
ISO 21501-4does not define the leak-test method. It governs the particle counter used to perform it.
Specialised aerosol route

Solid and PSL aerosol for sensitive filter media

Some semiconductor and aerospace applications use filter media — PTFE membrane among them — where an oil-based liquid challenge aerosol is unsuitable or is excluded by the specification. For those cases Topas offers the ATM 240/L suspension aerosol generator, which produces PSL and other solid-particle aerosols with integrated droplet drying, at high concentration.

This is a specialised route. It is not the standard cleanroom filter-integrity generator for every installation, and it should be considered only where the exact application and the media compatibility have been verified for the project. The ATM 240/L is documented by Topas in the context of EN 1822 and ISO 29463 filter-efficiency testing.

View the ATM 240/L →
Topas ATM 240/L suspension aerosol generator with integrated drying, used to produce PSL and other solid-particle test aerosols
Topas ATM 240/L — suspension aerosol generation with integrated droplet drying.
Technologies

Integrity-test measurement technologies

Topas ATM 228 mobile aerosol generatorTopas · Aerosol generatorATM 228Generates the controlled upstream challenge aerosol.
  • 20 – 250 L/h
  • Integrated brushless compressor
  • Max. 20 kPa counter-pressure
  • DEHS / PAO
View product →Topas DIL 544 automatic mobile dilution systemTopas · Automatic dilution systemDIL 544Automatically maintains the upstream-reference dilution ratio at the counter flow.
  • 1:100
  • 28.3 L/min
  • Automatic adjustment
View product →Topas DIL 554 manually adjustable mobile dilution systemTopas · Manual dilution systemDIL 554Provides manually adjusted static dilution for the upstream-reference measurement.
  • 1:100
  • 28.3 L/min
  • Mobile operation
View product →Topas CPA 341 cleanroom particle analyserTopas · Particle counterCPA 341Measures the upstream reference and the downstream scan.
  • 0.3 – 10 µm
  • 28.3 L/min
  • 5 size classes
  • ISO 21501-4
View product →Topas SYS 529 rectangular isokinetic sampling probeTopas · Sampling probeSYS 529Rectangular isokinetic scan probe matched to a 28.3 L/min particle counter.
  • 28.3 L/min
  • 31 – 47 cm/s
  • Rectangular inlet
View product →Topas SYS 528 rectangular isokinetic sampling probeTopas · Sampling probeSYS 528Rectangular isokinetic scan probe matched to a 50 L/min particle counter.
  • 50 L/min
  • 31 – 47 cm/s
  • Rectangular inlet
View product →
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Product selectionInstalled filter integrity testing Products relevant to installed-filter integrity applications.Open search → Product selectionInstalled filter leak scanning Probes and scanning technologies for downstream leak localisation.Open search → Product selectionAerosol generation Challenge-aerosol generators across the Precision Environment portfolio.Open search → Product selectionAerosol dilution Dilution systems for high-concentration upstream reference measurement.Open search →
Cleanroom & Controlled Environment Solutions →

Related methods

Conceptual particle-concentration recovery profile following a controlled challengeRecovery Time MeasurementCharacterise particle-concentration decay following a controlled challenge.Explore method → Topas CFG 291 fog generator used to make controlled-environment airflow visibleAirflow VisualisationObserve flow direction, disturbance, transitions and protected-zone behaviour.Explore method → Safety-cabinet qualification architecture with aerosol source and measurement positionsSafety Cabinet TestingFilter-integrity and airflow-verification routes for applicable cabinets.Explore method →

Installed-filter integrity system configuration

Share the filter type and installation, the airflow and duct conditions, the intended challenge aerosol, the upstream and downstream measurement method and the applicable standard or project specification.

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