What is HEPA Filter Integrity Testing?
A High Efficiency Particulate Air (HEPA) filter is rated to capture ≥99.97% of particles ≥0.3 µm. Integrity testing — sometimes called DOP (Dioctyl Phthalate) or PAO (Poly-Alpha Olefin) testing after the aerosol challenge agents historically used — confirms that the filter media, frame seal, and housing are all leak-free after installation.
The Test Method
- A polydisperse aerosol challenge is injected upstream of the filter at a concentration typically between 10–100 µg/L.
- A photometer or particle counter is scanned across 100% of the downstream filter face at a rate of ≤5 cm/s.
- Penetration exceeding 0.01% (for ISO 5 applications) indicates a leak requiring repair or replacement.
Regulatory Requirements
- USP 797: HEPA integrity testing required at installation, after any filter maintenance, and at recertification intervals (≤6 months for ISO 5 PECs).
- NSF/ANSI 49: Governs biosafety cabinet HEPA certification; requires scan testing plus airflow velocity and containment testing.
- IEST-RP-CC034: Industry recommended practice for HEPA/ULPA filter leak testing methods.
PAO vs. DOP: Is There a Difference?
Modern testing almost exclusively uses PAO (Emery 3004 or equivalent) because it is non-toxic and non-carcinogenic, unlike the original DOP (Dioctyl Phthalate). The test methodology and acceptance criteria are identical. Specifications that reference "DOP testing" accept PAO-based results.
What a Good Test Report Looks Like
Your certification report should include: filter model and serial number, upstream challenge concentration, scan rate, downstream penetration readings at multiple locations, and a clear pass/fail determination. Any corrective action taken (re-sealing, patching, or replacement) should also be documented.