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 |