TL;DR
A particle count exceedance is usually a failed HEPA filter, a damaged ceiling tile or FFU seal, or a personnel gowning breach. Locate the source with a particle counter before taking corrective action.
What you might see
- ISO classification particle count above limit at one or more sample locations
- particle alarm on the continuous monitoring system
- particle count elevated near one FFU or ceiling panel
- particle event correlated with a gowning or personnel ingress
Likely causes
HEPA filter pinhole failure or bypass leak at the filter frame seal
FFU motor or fan failure reducing air velocity and HEPA efficiency
Ceiling tile or wall panel joint open, allowing unfiltered room air to short-circuit
Gowning violation introducing particles with personnel at ingress
Required tools
- Handheld particle counter
- Anemometer for face velocity measurement
- HEPA filter frame sealant
- ISO 14644-1 sample location plan
Safety first
- Work inside the cleanroom during a particle investigation requires full cleanroom gowning even though the zone is in a non-conforming state. Minimize personnel in the affected zone.
- When replacing a HEPA filter, the downstream room will be exposed to unfiltered air. Evacuate all sensitive products before removing a HEPA filter.
Procedure
- 1
Identify the location of the elevated particle count from the monitoring system or by sampling all zones with a handheld counter.[1]
- 2
Hold a handheld particle counter 150 mm below each HEPA filter face in the zone of exceedance while the FFU is running. A count spike below a filter indicates a filter bypass or pinhole.
- 3
Check the FFU fan speed on each unit in the exceedance zone. A reduced face velocity confirms a failing motor or fan.
- 4
Inspect the HEPA filter frame seal at the ceiling grid. Re-seal or replace any frame seal that is visibly damaged or separated.[1]
- 5
Inspect all ceiling tile and wall panel joints in the exceedance zone for gaps. Seal any open joint with the approved sealant.
- 6
Review the gowning log for the exceedance period. If a gowning deviation is identified, re-train the personnel and update the gowning procedure.
- 7
Perform a full ISO classification count per ISO 14644-1 in the affected zone after corrective action. Accept the zone only when all sample points are below the class limit.
Sources
Terra Universal Terra Universal hardwall cleanroom Cleanroom Equipment / FFU general technical documentation, Terra Universal
Terra Universal cleanroom general HEPA testing and ISO 14644-1 classification procedures (general)
More guides for Terra Universal Terra Universal hardwall cleanroom
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Pressure differential loss is usually an FFU speed reduction, an exhaust air increase, or a wall panel seal failure. Check FFU face velocity and room seal integrity before adjusting any fan speed.
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