Overview
ISO 21501-4:2018/Amd 1:2023 is an amendment to the international standard for determining particle size distribution by single particle light interaction methods. Specifically, it focuses on light scattering airborne particle counters (LSAPC) designed for clean spaces such as controlled environments and cleanrooms. This amendment refines methodologies related to evaluating counting efficiency and introduces additional testing methods to improve accuracy and traceability in measuring airborne particle size and concentration.
Key Topics
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Counting Efficiency:
The amendment enhances the definition of counting efficiency by including the ratio of particle number measured by an LSAPC to that introduced to it within a given sampling time. Recognizing variability in particle losses, it recommends tolerance adjustments depending on particle size, especially for particles larger than 5 µm.
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Testing Methods:
Two primary methods for evaluating counting efficiency are detailed:
- Parallel Comparison Method: Compares particle counts between the LSAPC under test and a reference instrument using monodisperse particles such as polystyrene latex (PSL) spheres. It includes aerosol generation, conditioning, and size classification using droplet evaporation and differential mobility analysis.
- Generator Method: Uses an inkjet aerosol generator (IAG) producing monodisperse particles for precise particle number standards, suitable for sizes ranging from 0.5 µm to 10 µm. This method evaluates both intrinsic optical system performance and transport efficiency through sampling probes.
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Particle Generation and Conditioning:
Detailed procedures address minimizing measurement bias by drying aerosols, removing impurities, and conditioning particles electrically to ensure accurate and repeatable results.
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Traceability and Calibration:
The amendment emphasizes metrological traceability by calibrating LSAPCs against reference instruments at National Metrology Institutes (NMIs). It provides guidelines for establishing measurement consistency via inter-comparisons and validated procedures.
Applications
ISO 21501-4:2018/Amd 1:2023 is essential for industries and facilities requiring stringent airborne particle monitoring, including:
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Cleanrooms in Pharmaceutical and Semiconductor Manufacturing:
Ensures particle counters accurately monitor contamination and maintain cleanroom classification to prevent product defects.
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Healthcare and Hospital Environments:
Supports air quality control to reduce airborne pathogen transmission risks by verifying counter precision.
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Environmental Monitoring and Research:
Provides standardized methods for assessing airborne particulate pollution with high confidence in particle size and concentration data.
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Calibration Laboratories and Metrology Institutes:
Offers rigorous procedures for calibrating particle counters used in various industrial and scientific environments.
Related Standards
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ISO 21501 Series:
Includes other parts related to particle size and concentration measurement techniques, supporting comprehensive particle characterization.
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ISO 15900 and ISO 27891:
Standards referenced for particle size classification methods such as differential electrical mobility classifiers (DEMC) and aerodynamic aerosol classifiers (AAC).
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ISO/IEC Directives Part 1 and Part 2:
Offer fundamental guidance on developing and maintaining international standards, including editorial and procedural rules.
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ISO 21501-4:2018 (Base Standard):
The previously published version which this amendment updates.
Practical Value
The amendments introduced in ISO 21501-4:2018/Amd 1:2023 enhance the accuracy, reliability, and traceability of particle size distribution measurements using light scattering airborne particle counters. By defining improved counting efficiency criteria and introducing a robust generator method alongside the traditional parallel comparison, the standard supports more precise calibration essential for cleanroom monitoring, calibration labs, and environmental control.
Organizations utilizing LSAPCs benefit from:
- Improved measurement confidence for critical particle sizes.
- Better standardization across global operations.
- Reduced risk of contamination due to reliable particle detection.
- Alignment with international metrological frameworks for quality assurance.
Adopting this amendment ensures conformity with current best practices in airborne particle measurement and maintains compliance with established clean space monitoring requirements.
Keywords: ISO 21501-4 amendment, airborne particle counter, light scattering particle measurement, counting efficiency, cleanroom particle monitoring, particle size distribution, aerosol calibration, inkjet aerosol generator, metrological traceability, particle counter calibration.
Open preview (PDF)Determination of particle size distribution — Single particle light interaction methods — Part 4: Light scattering airborne particle counter for clean spaces — Amendment 1
