LAF · Calibration procedure
HEPA filter integrity
Challenges the HEPA filter with an oil aerosol (PAO or DOP) upstream and scans the whole downstream face and seal with a photometer probe to detect leaks.
PURPOSE
Why this is checked
A pinhole or seal leak lets unfiltered air into the Grade A zone even when average velocity and particle counts look acceptable. The integrity scan detects such leaks so they can be repaired before they contaminate work.
Frequency
Typically every 6 months (some sites test HEPA integrity annually), and after filter replacement, relocation or major repair, as defined in your SOP.
Learn how the LAF worksYOU WILL NEED
Standards & tools
- Aerosol generator producing a polydisperse PAO (poly-alpha-olefin) or DOP aerosol
- Calibrated aerosol photometer
- Alternatively, a discrete particle counter method as described in ISO 14644-3
BEFORE YOU START
Prerequisites
- Air velocity checked and within limits
- Upstream sample port accessible; diffuser or grille removed if needed
- Unit cleaned before the test and plan to clean after it (aerosol leaves an oil residue)
PROCEDURE
Step by step
- 1Introduce the aerosol upstream of the HEPA filter and measure the upstream concentration (typically 10–100 µg/L, often about 20 µg/L); set this as 100% on the photometer.
- 2Scan the entire downstream face of the filter with the probe about 2–3 cm from the surface, in slightly overlapping strokes, at no more than about 5 cm/s.
- 3Scan the full perimeter, including the gasket and the frame-to-housing seal.
- 4Where the reading exceeds the limit, hold the probe still to confirm and mark the leak location.
- 5Record the maximum penetration found and recheck the upstream concentration at the end.
RECORD
Example observation table
| Location | Upstream concentration (µg/L) | Max. downstream reading (% of upstream) | Result |
|---|---|---|---|
| Filter face, zone 1 | 20.0 | 0.002 | Pass |
| Filter face, zone 2 | 20.0 | 0.003 | Pass |
| Filter face, zone 3 | 20.0 | 0.001 | Pass |
| Perimeter seal | 20.0 | 0.002 | Pass |
CALCULATION
How to calculate the result
Penetration (%) = Downstream concentration ÷ Upstream concentration × 100
- Upstream = 20.0 µg/L; highest downstream reading in zone 2 = 0.0006 µg/L
- Penetration = 0.0006 ÷ 20.0 × 100 = 0.003%
- Below a typical leak limit of 0.01%: Pass
ACCEPTANCE CRITERIA
Pass if
- No point with penetration greater than 0.01% of the upstream concentration (typical leak criterion), as defined in your SOP.
- Upstream concentration within the range required by the method at the start and end of the test.
IF IT FAILS
What to do
- Stop using the unit.
- Repair small face leaks with an approved sealant if the manufacturer allows and the total repaired area is within the permitted limit; otherwise replace the filter.
- Reseat or replace a leaking gasket.
- Repeat the integrity test, then re-check velocity and particle count before release.
MORE
Other LAF calibrations
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.