ISO 14644-3 Cleanroom HEPA Filter Integrity Testing: Photometer vs Particle Counter
A technical comparative analysis of aerosol photometer scanning methods versus discrete particle counters for cleanroom in-situ filter leak detection.
Verifying the integrity of installed HEPA and ULPA filters is a core requirement of ISO 14644-3 and GMP Annex 1. Two primary methodologies exist for in-situ leak testing: the Aerosol Photometer Method and the Discrete Particle Counter (DPC) Method.
The Photometer Advantage
Aerosol photometers (such as the ATI 2i) measure aerosol mass concentration using forward light scattering. When paired with a Laskin-nozzle aerosol generator generating challenge aerosol (such as PAO-4), the photometer allows continuous, real-time probe scanning at speeds up to 5 cm/second. Any pinhole leak exceeding 0.01% of upstream challenge concentration is immediately detected.
When Particle Counters are Required
In ultra-clean environments (such as ISO Class 3 microelectronics fabrication), high-concentration oil aerosols can leave residue on sensitive equipment. In these applications, low-concentration microspheres paired with discrete particle counters are preferred.
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