Tuesday 29 August 2023

New ISO standard: Airborne particle sampling techniques


The latest part of ISO 14644 was published last week (part 21). This covers particle counters (light scattering aerosol particle counters).


ISO/TR 14644-21:2023 Cleanrooms and associated controlled environments — Part 21: Airborne particle sampling techniques.



The main points of interest that I've picked out from the standard are:

  • The LSAPC should be situated lower than the sample height to avoid sampling upward through tubing.
  • It is best to avoid tubing if possible.
  • Tubing should be as short as possible. However, the standard acknowledges the complexities of fitting tubing in RABS and isolators for fixed counters. It recommends that a particle loss assessment be conducted.
  • Different isokinetic probes are recommended for counters of different flow rates e.g. 28 l/m vs. 50 l/m and in relation to different air velocities. The acceptable particle loss (sampling error) from the use of an isokinetic probe is up to 5%.
  • Guidance is provided on isokinetic probe orientation in terms of the number of degrees permitted (target of 00, no greater than 200).
  • For tubing materials, stainless steel is preferred, followed by Bev-a-line, with Tygon suitable for higher temperatures.
  • With tubing length, this should be less than 1 metre, although 2 metres could be justified for fixed particle counters in a RABS provided the number of bends does not exceed 1 ( ≥5.0 ┬Ám particle losses reach 20% at 2 metres (for 10 mm diameter tubing). If 2 or 3 bends are required, a risk assessment is needed.
  • With tubing bends, the larger the radius the better with 15 cm being the starting point (depending on the flow rate and diameter).


This part is formally linked to ISO 14644 parts 1 and 2 (and these parts form part of EU GMP).

The standard is available from ISO or via your national standards organization.


 Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)

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