ISO 8573-4:2019

Overview

ISO 8573-4:2019 - Compressed air - Contaminant measurement - Part 4: Particle content - specifies methods for sampling compressed air and selecting suitable measuring equipment to determine particle size and particle concentration (by number). The standard describes measurement limitations, evaluation and uncertainty considerations, and reporting formats used to assess particle-related purity classes in accordance with the ISO 8573 series. It reports the combined particle content (solid + liquid) and excludes mass‑based concentration (see ISO 8573‑8) and non‑isothermal condensation/evaporation scenarios.

Key Topics

• Scope & purpose
  • Sampling procedures and guidance for choosing measuring instruments.
  • Reporting particle size and number concentration for compressed air.
• Measurement methods
  • Sampling-disc microscopy (light optical microscopy) - practical for particles ≥ 5.0 µm.
  • Scanning electron microscopy (SEM) - capable down to ≈ 0.005 µm.
  • Optical particle counters / optical aerosol spectrometers (OPC / OAS) - typical range ~0.06 µm to ≤100 µm.
• Sampling techniques
  • Full‑flow and partial‑flow sampling; guidance on isokinetic sampling and diffusers (see informative annexes).
  • Considerations for sampling duration, flow measurement, and avoiding contamination.
• Instrument considerations
  • Instrument selection, calibration, coincidence and dilution, and suitability verification with manufacturers.
• Evaluation & reporting
  • Conversion to reference conditions (20 °C, 100 kPa, zero water vapour pressure).
  • Uncertainty assessment and recommended content for a test report.
• Limitations
  • Does not separate liquid vs solid fractions (use ISO 8573‑2, ISO 8573‑7 for specific fractions).
  • Mass‑based particle concentration is outside this part (ISO 8573‑8).

Applications

ISO 8573-4:2019 is used by professionals who need to quantify airborne particulates in compressed air systems for quality, safety and process control:

• Compressor and compressed‑air treatment manufacturers
• Industrial maintenance and reliability engineers
• Cleanroom and pharmaceutical quality managers
• Food & beverage, electronics and semiconductor production teams
• Test laboratories performing compressed air purity assessments Practical uses include compliance testing to ISO 8573‑1 particle purity classes, selecting filtration/dryer systems, validating compressed air for critical processes, and generating traceable test reports.

Related Standards (if applicable)

• ISO 8573‑1 - Contaminants and purity classes (overall classification)
• ISO 8573‑2 - Oil content by mass
• ISO 8573‑7 - Viable microbiological particles
• ISO 8573‑8 - Particle concentration by mass
• ISO 21501‑1 / ISO 21501‑4 - OPC / OAS instrument methods
• ISO 3857‑4, ISO 80000‑1 - Terminology and units

Keywords: ISO 8573-4:2019, compressed air, particle content, particle concentration, particle size, sampling, optical particle counter, purity classes.