ISO 21501

For determination of particle size distribution for single-particle light-interaction methods 

This standard focuses primarily on calibration/verification methods used to ensure particle counters size and count particles accurately, using a traceable reference instrument. This standard is very important for those carrying out cleanroom routine environmental monitoring or classification as it is mandated in ISO 14644-1 & -2:2015 which are referenced in the USA CGMP and EU GMP Annex 1.

Adherence to ISO 21501 can maximize confidence that multiple instruments (including those from different manufacturers) closely correlate in terms of particle counts recorded, which, for example, is critical for classifying/validating/monitoring cleanrooms to ISO 14644, USA CGMP and EU GMP Annex 1.

This standard covers air particle counters, liquid particle counters and aerosol spectrometers, and is divided into 4 parts based on instrument type.  

  • Part 1: covers light scattering aerosol spectrometers used to measure particles suspended in a gas
  • Part 2: covers light scattering liquid-borne particle counters
  • Part 3: covers light extinction (obscuration) liquid-borne particle counters
  • Part 4: covers light scattering airborne particle counters

Who Should Adopt ISO 21501?

  • Pharmaceutical manufacturers that carry out routine environmental monitoring/periodic classification for all classes of cleanrooms used in the GMP environment as both CGMP and GMP Annex 1 reference ISO 14644 and ISO 14644 references ISO 21501-4 for air particle counters
  • Pharmaceutical manufacturers making parenteral drugs as ISO 21501-3 is used to calibrate the light obscuration particle counters used in final product quality testing to USP<787>, <788>, EP2.2.19
  • Labs and manufacturers that need to:
    • Evaluate cleanliness of pure water and chemicals
    • Measure number and size distribution of particles in various liquids
  • Any manufacturer of products that require processing/assembly in a cleanroom environment classified under ISO 14644:2015