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

Monitoring particle contamination levels is required in various fields, e.g. in the electronic industry, in the pharmaceutical industry, in the manufacturing of precision machines and in medical operations. Particle counters are useful instruments for monitoring particle contamination in air. The purpose of this part of ISO 21501 is to provide a calibration procedure and verification method for particle counters, so as to minimize the inaccuracy in the measurement result by a counter, as well as the differences in the results measured by different instruments.

ISO 21501-4 describes a calibration and verification method for a light scattering airborne particle counter (LSAPC), which is used to measure the size and particle number concentration of particles suspended in air. The light scattering method described in ISO 21501-4 is based on single particle measurements. The typical size range of particles measured by this method is between 0.1 µm and 10 µm in particle size.

Instruments that conform to ISO 21501-4 are used for the classification of air cleanliness in cleanrooms and associated controlled environments in accordance with ISO 14644-1, as well as the measurement of number and size distribution of particles in various environments.

ISO 21501-4:2007 is the current version of this standard. The following is the scope defined within this standard:

- size calibration
- verification of size setting
- counting efficiency
- size resolution
- false count rate
- maximum particle number concentration
- sampling flow rate
- sampling time
- sampling volume
- calibration interval
- test report

Retrieved from the ISO website and "Understanding ISO 21501-4" on 02/04/2014