Cleanroom Qualification • HVAC • GMP

HEPA Filter Leak Test: Procedure and Acceptance Criteria

A practical guide to in-place HEPA filter integrity testing in pharmaceutical cleanrooms, including aerosol challenge, downstream scanning, pass/fail decisions, repairs, and report requirements.

Technical guideFor QA, Engineering & ValidationUpdated September 2026

HEPA Filter Leak Test: Procedure and Acceptance Criteria

Quick answer

A HEPA filter leak test challenges the installed filter with an appropriate aerosol upstream, then scans the downstream filter face, frame, and seals with a photometer or another justified method to find localized leakage. In FDA’s aseptic-processing guidance, a probe reading equal to 0.01% of the upstream challenge is considered indicative of a significant leak. Treat that value as guidance for the described method—not a universal limit for every filter, facility, or test protocol. Define the method and acceptance criterion in the approved site protocol.

HEPA filter leak testing verifies that the installed filter assembly performs as intended after installation and during its service life. It is especially important where filtered air protects exposed sterile product, critical surfaces, or a classified cleanroom. The test looks for bypass around the filter media or through defects in the media, frame, seal, or housing. It does not replace cleanroom classification, airflow testing, pressure-differential checks, or environmental monitoring.

Regulatory and technical references support a planned, documented approach. EU GMP Annex 1 includes installed filter-system leakage and integrity testing in cleanroom and clean-air-equipment qualification, and calls for final-filter integrity testing during periodic requalification. The FDA’s aseptic-processing guidance describes an in-place aerosol scan and gives a 0.01% upstream-challenge reading as an indicator of significant leakage. ISO 14644-3 provides cleanroom test methods; the facility should identify the applicable edition and method in its controlled procedure. [EU GMP Annex 1] [FDA guidance] [ISO 14644-3]

Important distinction: A filter’s rated particle-removal efficiency and an installed leak test answer different questions. Efficiency testing characterizes filter media performance; in-place leak testing searches for localized defects and bypass at the media, frame, and seal. A high nominal filter rating does not prove that the installed assembly is leak-free.

What is a HEPA filter leak test?

A HEPA filter leak test—often called an installed filter integrity test or aerosol challenge test—is an in-situ examination of a filter and its mounting system. A known aerosol challenge is introduced upstream. A calibrated instrument samples the downstream air while a probe is moved across the full filter face and around its perimeter. A localized signal is compared with the upstream challenge to determine whether leakage exceeds the approved criterion.

Media integrity

Detects a pinhole, tear, or other localized defect in the filter medium.

Seal and frame

Checks gasket contact, frame joints, and the filter-to-housing interface for bypass.

Installation quality

Confirms the installed assembly can meet the defined contamination-control need under test conditions.

HEPA filter leak test acceptance criteria

Acceptance criteria should be approved before execution and tied to the filter type, room use, test method, instrument capability, applicable regulation or standard, and manufacturer requirements. The FDA guidance for aseptic processing states that a single probe reading equivalent to 0.01% of the upstream challenge is indicative of a significant leak; it describes replacement or, when appropriate, limited-area repair followed by confirmatory retesting. This is a widely referenced benchmark for photometer scanning, but the guidance is nonbinding and this number should not be presented as a single mandatory threshold for every cleanroom test. FDA guidance, HEPA leak testing section.

EU GMP Annex 1 requires installed filter-system leakage and integrity testing where relevant, and includes final-filter integrity testing in cleanroom requalification. It does not prescribe one universal numerical local-penetration limit in the cited provisions. Therefore, site procedures should state the selected limit and its scientific, regulatory, and technical basis. EU GMP Annex 1, sections 4.25 and 4.32.

Criterion	What the protocol should establish	Evidence to record
Challenge quality	Suitable aerosol and a uniform, sufficient upstream concentration for the selected instrument/method.	Aerosol type, generator settings, upstream concentration, measurement locations, and any uniformity check.
Scan coverage	Complete coverage of the downstream face, frame, seals, and relevant housing interface using the approved probe path and technique.	Filter ID, dimensions, scan map or sequence, probe position/speed, and areas inaccessible or treated by an alternate method.
Leak response	Local downstream reading remains below the approved threshold relative to the upstream challenge.	Peak and sustained readings, location, calculated penetration, and instrument status.
Post-repair status	Any permitted repair is verified by a confirmatory scan; wider retesting follows the site procedure.	Repair material/area, authorization, repair record, retest result, and final disposition.
System condition	Test is performed in the specified HVAC configuration and airflow condition, with no test-induced damage or unassessed system change.	Fan state, room status, pressure/airflow condition, test date, and relevant deviations.

A filter-efficiency rating (for example, a nominal retention claim) is not the same as a downstream localized leak criterion. Do not copy a number from a different filter grade, instrument, or standard without confirming applicability.

Equipment and materials for aerosol leak testing

Aerosol generator appropriate for the selected challenge and test set-up.
Approved challenge aerosol with controlled physicochemical properties and an assessment of suitability for the room and process.
Calibrated aerosol photometer with a suitable scan probe, or another qualified instrument and method.
Current calibration status, zero/background checks, and any manufacturer-recommended accessories.
Filter register, approved protocol, cleanroom entry controls, and suitable PPE.
Means to record upstream challenge and downstream readings with filter locations clearly traceable.

The FDA guidance names DOP and PAO as examples of aerosols for HEPA leak testing, while also emphasizing that alternative aerosols should be evaluated for relevant properties and potential impact, including whether they could promote microbial growth. Select the challenge aerosol under the facility’s safety, contamination-control, equipment-compatibility, and regulatory procedures; do not substitute an aerosol solely because it is commonly used elsewhere. FDA guidance.

HEPA filter leak test procedure: step by step

1Review the protocol and filter history

Confirm the filter identifier, location, grade/specification, room classification, last test, previous repairs, and reason for testing. Verify that the approved protocol defines the aerosol, instrument, upstream challenge, scan pattern, probe technique, acceptance limit, and response to failure.

2Confirm the test instrument and room condition

Check photometer identification, calibration status, zero/background response, probe integrity, and generator condition. Place the HVAC system in the defined test configuration and confirm the filter is dry, undamaged, and accessible. Record room and system conditions that can affect interpretation.

3Introduce the aerosol upstream

Generate and introduce the challenge upstream of the filter using the approved connection point. Allow the challenge to mix as required by the test method. Measure the upstream concentration at the protocol-defined point or points and verify it is within the range needed for reliable instrument response. An inadequate or nonuniform challenge can invalidate the scan.

4Set the instrument reference

Set or verify the instrument’s upstream reference according to its operating instructions and the approved procedure. Perform any required zero check and ensure the photometer reads the challenge consistently. Document the value and calculation basis used for percentage penetration.

5Scan the downstream filter face and perimeter

Move the probe across the complete downstream surface in a controlled, overlapping pattern. Scan the entire filter face, frame, gasket/seal, and relevant housing joints. Maintain the probe distance and scan speed required by the approved method; the FDA guidance describes scanning about 1–2 inches from the filter face and a sampling rate of at least 1 cubic foot per minute for its described photometer procedure. Use the protocol and instrument instructions for the actual job.

6Investigate any elevated reading

Pause at a localized indication and follow the protocol’s confirmation rules. Check for probe position, turbulence, nearby aerosol sources, and instrument stability before classifying a true leak. Record the highest indicated reading, exact location, duration, and percentage of upstream challenge. Do not dismiss a signal without documenting the technical rationale.

7Repair or replace under control

If the filter fails, initiate the site deviation process. A qualified person may repair a limited area only where allowed by the filter manufacturer, applicable procedure, and approved quality decision. Replace the filter when damage is extensive, repair is not permitted, or the test remains unacceptable. Assess whether room use or product protection was affected.

8Retest and restore the system

After repair, perform the required confirmatory scan over the repaired location and any broader area specified in the protocol. After replacement, test the newly installed assembly in place. Remove or control test residues as required, restore the system to its approved operating state, and confirm relevant room conditions before release for use.

9Review results and approve the report

Compare results against the predefined acceptance criteria. Resolve deviations, confirm attachments and instrument records, and obtain required QA/Engineering review. A contractor’s certificate alone does not replace the manufacturer’s responsibility to define specifications, method, criteria, and satisfactory completion.

How is percentage penetration calculated?

For a photometer scan, localized downstream leakage is generally expressed relative to the upstream challenge concentration:

Local penetration (%) = (downstream probe reading ÷ upstream challenge reading) × 100

For illustration only, if the upstream challenge is 100 units and a confirmed localized probe reading is 0.008 units, the calculated penetration is 0.008%. Compare the result with the acceptance limit written in the approved protocol. The example is not a recommended facility limit and does not account for instrument-specific settings, corrections, or method requirements.

Common causes of HEPA filter test failure

Damaged media from handling, installation, maintenance, or contact with tools.
Compressed, twisted, aged, or incorrectly seated gaskets.
Loose clamps, frame defects, poor sealant application, or leakage at housing joints.
Insufficient or uneven upstream aerosol challenge.
Probe scan gaps, excessive scan speed, incorrect probe distance, or incomplete perimeter coverage.
Unstable instrument zero, overdue calibration, incorrect range, or poor connection tubing.
Airflow configuration different from the approved test condition.

A failed result should trigger an investigation into both the physical filter assembly and the test execution. Repeating the scan without investigating the cause can obscure a genuine defect or create unreliable evidence.

What to do when a HEPA filter fails

Protect the process: assess whether the affected room or critical zone was in use since the last acceptable test and place it under appropriate quality control.
Open a deviation: document the failure, filter identity, leak location, test conditions, and immediate containment.
Assess product and area impact: use batch history, environmental monitoring, airflow data, pressure trends, maintenance events, and product exposure information.
Determine cause: examine installation, gasket, frame, media, maintenance practice, test setup, and instrument performance.
Repair or replace: use approved methods and qualified personnel; do not use unapproved sealants or repairs.
Retest and requalify: complete the required filter integrity retest and any room requalification tests justified by the impact or change.
Prevent recurrence: implement and verify corrective and preventive actions, such as improved handling, installation checks, or test-method training.

Where a failure may have affected sterile operations, the quality impact assessment should be scientifically justified and documented. A filter passing a later retest does not, by itself, establish that previously manufactured product was unaffected.

Frequency: when should the test be performed?

Set frequency through applicable GMP requirements, cleanroom requalification rules, filter criticality, system design, maintenance history, and quality risk management. FDA’s aseptic-processing guidance says leak tests should be performed at installation and at suitable intervals; it gives twice yearly for an aseptic processing room as an example and recommends additional testing after events such as unacceptable air quality, renovations that may disturb structures, or investigations into sterility failures. EU GMP Annex 1 lists final-filter integrity testing as a minimum element of cleanroom requalification and sets maximum requalification intervals of six months for Grade A/B and twelve months for Grade C/D areas. These are cleanroom requalification intervals; a site may need additional testing based on risk, change, or local requirements. FDA guidance EU GMP Annex 1, section 4.32.

Additional testing is commonly considered after filter replacement, ceiling or housing work, HVAC changes, pressure or airflow anomalies, visible damage, or a relevant contamination investigation. The facility’s change-control and cleanroom requalification procedure should determine the scope.

HEPA filter leak test report: what to include

Approved protocol number, revision, date, test purpose, and acceptance criterion.
Room name/classification, filter ID, location map, filter manufacturer/model, and installation or replacement date.
Instrument model, serial number, calibration due date, generator identification, probe type, and tubing configuration.
Aerosol type, generator settings, upstream challenge values, reference/zero checks, and relevant test setup readings.
Scan pattern, probe distance and speed, scan coverage, inaccessible areas, and any method deviations.
Maximum downstream signal, leak location, calculated penetration, acceptance decision, and raw data or instrument printout.
Repair/replacement details, retest results, deviation/CAPA references, and final QA/Engineering approval.
Post-test restoration confirmation and any follow-up room qualification or operational checks.

Ensure records are attributable, legible, contemporaneous, original, and accurate, with complete audit trails where electronic records are used. See the site’s ALCOA+ data-integrity principles.

HEPA filter integrity testing checklist

Approved protocol and site-specific acceptance limit available before testing.
Correct filter ID, scan coverage, instrument, probe, and aerosol selected.
Instrument calibration and zero/background checks acceptable.
Upstream aerosol challenge is sufficient, stable, and representative for the method.
Entire downstream face, frame, seal, and relevant housing interface scanned and documented.
Any indication investigated; repairs are permitted, controlled, and confirmatory retested.
Deviations and potential product/room impact assessed before area release.
Final report reviewed and linked to cleanroom qualification and change records.

Key takeaways

A HEPA filter leak test checks the installed assembly for localized leaks and bypass; it is not simply a filter-efficiency rating test.
The core procedure is an upstream aerosol challenge followed by a systematic downstream scan of the face, frame, and seals.
FDA’s aseptic-processing guidance identifies 0.01% of upstream challenge as indicative of a significant leak for the described photometer method. Treat the figure in context and set the site acceptance criterion in an approved protocol.
EU GMP Annex 1 requires installed filter integrity testing where relevant and includes final-filter integrity testing during requalification, but does not set one universal leak percentage in those provisions.
Document the complete test, investigate failures, assess affected operations, and verify any repair or replacement by retesting.

Frequently asked questions

What is the purpose of a HEPA filter leak test?

It detects localized leakage through filter media or bypass around the filter frame, gasket, seal, or housing while the filter is installed. This helps show whether the filter assembly is suitable for its intended cleanroom or critical-zone use.

What is the acceptance limit for a HEPA filter leak test?

There is no single limit that automatically applies to every facility and method. FDA’s aseptic-processing guidance treats one probe reading equivalent to 0.01% of the upstream challenge as indicative of a significant leak for its described aerosol-photometer scan. The approved site protocol should define the applicable criterion and technical basis.

Does EU GMP Annex 1 specify a 0.01% leak limit?

The cited Annex 1 provisions require installed filter-system leakage/integrity testing as relevant and include final-filter integrity testing in cleanroom requalification. They do not set a universal numerical local-penetration acceptance value in those sections. Facilities should justify and document their own applicable limit.

How often should HEPA filters be leak tested?

Test at installation and at planned intervals defined by regulations, cleanroom requalification requirements, risk, and site procedures. FDA gives twice yearly for aseptic processing rooms as an example. EU GMP Annex 1 requires periodic requalification at maximum intervals of six months for Grade A/B and twelve months for Grade C/D, including final-filter integrity testing. Events such as filter replacement, HVAC work, or adverse air-quality results can require additional tests.

Is a HEPA filter efficiency test the same as a leak test?

No. An efficiency test characterizes the filter’s overall particle-removal performance. An in-place leak test scans for localized defects and bypass at the filter media, frame, and seal. FDA explicitly distinguishes these purposes in its guidance.

Which aerosol is used for HEPA filter leak testing?

Use an aerosol suitable for the instrument, filter, room, and process, selected and justified in the procedure. FDA guidance gives DOP and PAO as examples and advises evaluating alternatives for relevant physicochemical properties and possible microbial impact. Follow current site safety and contamination-control controls.

Can a leaking HEPA filter be repaired?

Sometimes a localized repair may be acceptable if the filter manufacturer and approved procedure allow it and Quality authorizes the repair. Extensive damage, an unrepairable defect, or repeat failure generally calls for replacement. Any repair must be followed by the specified confirmatory retest and documentation.

What should be scanned during the test?

Scan the entire downstream filter face and frame, including seals/gaskets and relevant housing joints. A protocol should define the scan pattern, overlap, probe distance and speed, and how difficult-to-access locations are covered.

Why is a sufficient upstream aerosol challenge important?

The downstream reading is interpreted relative to the upstream challenge. If upstream concentration is insufficient or uneven, a real leak may be missed or results may not be reliable. Confirm and record the challenge according to the method before scanning.

What should happen after a HEPA filter test failure?

Place the result under deviation control, evaluate room and product impact, investigate test execution and filter condition, and repair or replace under an approved process. Retest the affected area and perform any justified room requalification before returning the area to service.