ISO 21501-4: Light Scattering Airborne Particle Counter for Clean Spaces

ISO 21501-4 covers instrument calibration procedures to ensure air particle counter sampling measurement inaccuracies are reduced. A Counting Efficiency Test is also included as a final confirmation of air particle counting performance.

All GMP cleanroom operators/users must ensure the air particle counters used to classify and monitor their cleanrooms are compliant with ISO 21501-4 requirements.

ISO 21501-4 Parameters  Target Limit 
 Size calibration  ±5%
 Counting efficiency at first channel  50% ± 20%
 Counting efficiency at particle size 1.5-2.0 times first channel  100% ± 10%
 Instrument resolution (at manufacturer specified size)  ≤ 15%
 Zero count test   ≤ 1 count in 5 mins
 Max particle number concentration (specified by manufacturer)  ≤ 10%
 Sampling flow rate (volumetric)  ± 5%
 Sampling time  ± 1%
 Calibration interval  ≤ 1 year

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