In-place filter leak test
A test of an installed HEPA filter or filter bank in which a test aerosol is introduced upstream and measured downstream, finding leaks through the media, frame, gasket, or housing that a factory efficiency test cannot detect. It is performed at installation and at set intervals afterward.
Also called HEPA leak test, filter integrity test, DOP test, PAO test, aerosol scan test
What is an in-place filter leak test?
An in-place filter leak test challenges an installed HEPA filter with an aerosol upstream and measures what gets through downstream, proving the filter, gasket, and housing together. The DOE handbook recommends 0.05 percent maximum leakage as the acceptance criterion for in-place system tests.
In-place filter leak test: how it works
A generator introduces a polydisperse aerosol into the air upstream of the filter, and the upstream concentration is measured once it has mixed. Downstream, the technician either scans the filter face and its seal with a probe to find individual leaks, or samples the whole mixed airstream to measure a bank's overall leakage. Leakage is the downstream reading expressed as a percentage of the upstream concentration.
Where you meet the term
- In a cleanroom certification report, as a pass or fail result for every terminal filter.
- In a nuclear or containment exhaust system, as the acceptance and surveillance test for each HEPA stage.
- In the FDA aseptic processing guidance, which asks for leak tests at installation and at suitable intervals afterward.
How to check it
- Review the last test date and result. The certification report lists each filter, the test method, the result, and the date, and a filter disturbed since that date needs retesting. Owner check
- Perform the scan or system test. A qualified technician sets the upstream aerosol concentration, scans or samples downstream, and records the highest leakage found against the acceptance limit. Technician
Figures you will see
| Condition | Figure | What it tells you |
|---|---|---|
| DOE-HDBK-1169-2022 in-place system test acceptance | 0.05 percent maximum leakage | Read against the model documentation |
| FDA example interval for an aseptic processing room | Twice a year | Read against the model documentation |
In-place filter leak test: what it is not
- An in-place leak test is not an efficiency test. It finds leaks in the installation, and the filter's efficiency rating comes from its factory test.
- A passed test does not cover later disturbance. Ceiling work, a dropped tool, or a housing change can open a leak after the test date.
In-place filter leak test questions
What is the difference between a scan test and a system test?
A scan test moves a probe across the downstream face and seal of each filter to find individual leaks. A system test samples mixed air downstream of a whole bank and measures its total leakage, which is how nuclear exhaust stages are tested.
Why are HEPA filters retested after a fire?
Smoke and heat can damage media and seals. The DOE handbook recommends an in-place test within 24 hours for filters exposed to smoke from a fire, with replacement if the filter fails.
Does the test aerosol load the filter?
The aerosol is introduced at a controlled concentration for a short test, and the filter captures it like any other particle. Repeated heavy challenges add loading, which is one reason test concentration and duration are controlled.
Where this definition comes from
Written from government guidance, standards body publication material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- DOE-HDBK-1169-2022, Handbook for use with DOE-STD-1269-2022, Air Cleaning Systems in DOE Nuclear FacilitiesDOE handbook replacing the 2003 Nuclear Air Cleaning Handbook: primary, secondary, and tertiary confinement zones with air flowing toward the more contaminated zone and pressure differentials that prevent backflow under upset conditions; a 100 feet per minute rule of thumb for capture velocity across a primary confinement breach; positive seals at secondary barrier penetrations; bag-in bag-out side-access housings with upstream and downstream shutoff dampers and provisions for in-place testing; parallel housings with inlet and outlet isolation dampers; a recommended 0.05 percent maximum leakage acceptance for in-place HEPA system tests under ASME AG-1 Appendix TA; backup power for fans, dampers, and controls where safety documentation requires it; and stack guidance of exit velocity at least 1.5 times wind velocity with 3,000 feet per minute recommended, noting that high velocity is no substitute for proper stack location.
- Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing, Current Good Manufacturing PracticeFDA guidance recommending a positive pressure differential of at least 10 to 15 pascals between adjacent rooms of differing classification with doors closed, outward airflow sufficient to minimize ingress when doors open with door-open time strictly controlled, at least 12.5 pascals from an aseptic processing room to adjacent unclassified space, airflow for at least 20 air changes per hour as acceptable for ISO 8 supporting rooms, a critical area velocity of 0.45 meters per second (90 feet per minute) plus or minus 20 percent, and HEPA filter leak testing at installation and at intervals such as twice a year for the aseptic processing room.
- ASME N510, Testing of Nuclear Air Treatment SystemsIn-service testing of ASME N509 high-efficiency air treatment systems, arranged so a user selects relevant tests performed in a stated sequence with recommended minimum frequencies, and containing no acceptance criteria except where one test affects another, leaving acceptance to the system design basis.
- ISO 14644-3:2019, Cleanrooms and associated controlled environments, Part 3: Test methodsTest methods for cleanroom performance: air pressure difference, airflow volume and velocity, airflow direction and visualization, recovery time using the 100 to 1 ratio with a 10 to 1 ratio added in the 2019 edition for less clean rooms, installed filter system leakage, containment leakage, temperature, and humidity. Recovery testing is optional and its acceptance is agreed between customer and supplier.