iso-8573-4-particulate-matter-classes

By Paradorn Wannasung · Master’s in Marketing Communication · AERZEN Rental Thailand Published: 20 June 2026 · Reading time approx. 9 minutes

As AERZEN has understood since 1864, delivering compressed air is not simply about pressure and flow — it is about delivering air of a defined and verified quality. Solid particulate contamination is one of the three primary contamination categories in compressed air systems, and ISO 8573-4 provides the standardised test method for measuring it.

For engineers specifying compressed air systems — whether for pharmaceutical cleanrooms, food processing lines, electronics assembly, or general industrial use — understanding what ISO 8573-4 measures, how its classes map to ISO 8573-1 purity requirements, and what it means in practice for system design and maintenance is foundational technical knowledge.

The ISO 8573 Series — Context for Particulate Standards

ISO 8573 is a multi-part standard series governing compressed air quality. Understanding where Part 4 sits within the series prevents the common confusion between the purity classification document and the test method documents:

The relationship is direct: ISO 8573-1 defines what level of particulate is acceptable (the class). ISO 8573-4 defines how you measure whether you have achieved that class. Reference: ISO 8573-1:2010 and ISO 8573-4:2019

ISO 8573-1 Particulate Classes — What the Numbers Mean

Before examining the test method, the purity classes from ISO 8573-1 establish the target:

Source: ISO 8573-1:2010 Table 1 (solid particulate)

Class 1 is the most stringent — requiring very low counts across all three size bands, including the sub-micron range. This class is appropriate for semiconductor fabrication, sterile pharmaceutical processes, and optical component manufacturing.

Class 3–4 is typical for general industrial applications where solid particulate must be controlled but the process is not sensitive to sub-micron particles.

The particle size categories are physically significant:

• 0.1–0.5 µm: Sub-micron particles that pass through many standard filters — relevant in semiconductor and pharmaceutical environments
• 0.5–1.0 µm: Particles visible only under electron microscopy — critical for precision optical or electronic component handling
• 1–5 µm: Particles that cause wear in pneumatic actuators and precision valves, and visible contamination on high-gloss surfaces

ISO 8573-4:2019 — The Test Method

ISO 8573-4 specifies how solid particulate content in compressed air is measured. The current revision is the 2019 edition, which supersedes the 2001 version.

Measurement Principle

The standard defines two primary measurement approaches:

1. Gravimetric method (mass-based) Air is sampled through a filter membrane of defined pore size. The captured particulate mass is determined by weighing the filter before and after sampling. This method gives total particulate mass per unit volume but does not provide particle size distribution.

2. Particle counter method (count-based) A calibrated optical particle counter samples the compressed air stream and counts particles by size category. This method gives the particle count per m³ in each size band corresponding to ISO 8573-1 class boundaries.

Sampling Requirements

Correct sampling is critical — ISO 8573-4 is explicit about sampling point requirements:

• Sampling must occur at the point of use or at a defined representative point, not upstream of filtration
• The sampling probe must be positioned in the centre of the pipe cross-section, not at the wall where particle concentration differs
• Flow velocity at the sampling probe must be isokinetic (matching the bulk flow velocity) to avoid particle segregation by inertia
• Minimum sampling duration and volume are specified to ensure statistical validity

Isokinetic sampling is the most technically demanding requirement — if the probe velocity differs from the bulk flow, larger particles are over- or under-sampled relative to their true concentration. This is a common source of measurement error in field testing.

Calibration and Traceability

ISO 8573-4 requires that particle counters used for measurement be calibrated against reference particles of known size and concentration, with traceability to national measurement standards. This requirement ensures that measurements taken by different laboratories or instruments are comparable — a prerequisite for contractual specification compliance.

Sources of Solid Particulate in Compressed Air Systems

Understanding where solid particulate enters the system is essential for specifying the correct filtration strategy.

Source 1: Ambient Inlet Air

Atmospheric air contains particles from:

• Industrial particulate (dust, process emissions)
• Biological particles (pollen, bacteria, fungal spores)
• Traffic-related particulate (PM2.5, PM10)

In Thailand’s industrial zones — particularly in EEC coastal and industrial estate areas — ambient particulate loading can be significantly higher than European baseline conditions that some international standards implicitly assume. This affects inlet filter selection and replacement frequency.

Source 2: Compressor Internals

• Oil-lubricated compressors produce oil aerosol and oil vapour, which, when oxidised, form solid varnish particles
• Oil-free compressors eliminate oil-derived particulate entirely — a primary driver for specifying ISO 8573-1 Class 0 oil content alongside Class 1–2 particulate in sensitive processes

Source 3: Distribution System Degradation

• Pipe scale and rust in carbon steel distribution systems
• Polymer particles from degraded seals or flexible hose internal liners
• PTFE tape particles from threaded connections assembled without care

This is a frequently overlooked source — even a well-specified compressor with clean output can deliver particulate-contaminated air if the distribution system is degraded.

Source 4: Condensate and Downstream Components

Liquid water droplets in the distribution system carry dissolved and suspended particulate. Ineffective condensate management (failed drains, blocked separators) allows liquid slugs that carry concentrated particulate to point-of-use equipment.

Practical Filtration Strategy Aligned with ISO 8573-4

A three-stage filtration approach is standard for achieving Class 1–2 particulate at point of use:

Stage 1 — Coarse pre-filter (5–10 µm rating) Removes bulk particulate and liquid water droplets after the aftercooler. Protects downstream filters from rapid loading.

Stage 2 — Coalescence filter (1 µm or 0.01 µm rating) Coalesces fine aerosol droplets (oil and water) into drain-able liquid. Also captures particulate to its rating.

Stage 3 — Activated carbon filter (where oil vapour removal is required) Adsorbs gaseous hydrocarbons. Does not remove solid particles but is necessary for achieving Class 0 oil content in conjunction with an oil-free compressor.

For Class 1 particulate at point of use, a high-efficiency particulate filter rated 0.01 µm positioned after the coalescer is required.

Differential pressure monitoring across each filter stage is the practical tool for knowing when replacement is required — without it, filter loading is invisible until either pressure drop causes supply pressure problems or the filter is bypassed by overloading.

Connecting ISO 8573-4 to System Verification

For engineers responsible for commissioning a compressed air system or demonstrating compliance to customers or regulators, ISO 8573-4 provides the audit-ready test method.

Verification should be conducted:

• At initial commissioning
• After any significant modification to the compressor, filtration, or distribution
• At intervals defined in the quality management system (typically annually for Class 1–2 systems in pharmaceutical or food applications)

Test results should be documented as:

• Particle count per m³ per size band
• Flow conditions at time of measurement (pressure, temperature, flow rate)
• Instrument calibration certificate reference
• Sampling point identification

This documentation forms part of the compressed air quality management record — required under GMP frameworks and useful for demonstrating due diligence in any product quality investigation.

Case Study — Electronics Assembly Plant, EEC Zone (TEACHING_SAMPLE — simulated data for educational purposes)

Note: The following is a TEACHING_SAMPLE constructed for illustration. It does not represent data from a specific named customer.

An electronics assembly plant producing printed circuit boards required ISO 8573-1 Class 1 particulate air for SMT (surface mount technology) soldering processes and component pick-and-place operations.

Initial baseline measurement using an optical particle counter calibrated to ISO 8573-4 protocol revealed that the existing system was delivering Class 3 at the point of use — within specification for general industrial air but not for the precision SMT process.

Root cause analysis identified two contributing sources:

1. Distribution pipe sections in carbon steel showing internal rust — particulate entering from pipe degradation
2. Coalescence filters running without differential pressure monitoring, loaded well beyond effective capacity

Corrective actions:

• Replace corroded pipe sections with stainless steel in the precision process area
• Install differential pressure gauges on all filter stages with alert thresholds
• Add a final-stage 0.01 µm high-efficiency filter at the SMT room inlet

Post-correction measurement confirmed Class 1 particulate at the point of use. The plant incorporated the ISO 8573-4 protocol into its annual quality management audit schedule.

FAQ

Q1: Is ISO 8573-4 the same as ISO 8573-1? A: No. ISO 8573-1 defines the purity classes — the requirements. ISO 8573-4 defines the test method for measuring solid particulate to determine which class has been achieved. You need both: 8573-1 to specify the target, 8573-4 to verify compliance.

Q2: How frequently should particulate testing be conducted? A: The frequency depends on the criticality of the application and the requirements of the applicable quality management standard. For pharmaceutical GMP environments, annual verification is typical as a minimum; for semiconductor cleanrooms, more frequent monitoring is common. Consult the relevant regulatory framework for your industry.

Q3: Can an oil-free compressor alone guarantee Class 1 particulate? A: An oil-free compressor eliminates oil-derived particulate from the compressor stage, which is significant — but it does not address particulate from the distribution system, inlet air, or component degradation. Achieving Class 1 at point of use requires both an appropriate compressor and correctly specified, maintained filtration.

Q4: What is the difference between gravimetric and particle counter methods for ISO 8573-4 testing? A: The gravimetric method measures total mass of particulate captured on a filter — useful for regulatory reporting of mass concentration. The particle counter method gives count per size band — directly comparable to ISO 8573-1 class limits. For classification purposes, the particle counter method is more directly applicable.

Q5: How does ambient particulate in Thai industrial environments affect system design? A: Elevated ambient PM2.5 and PM10 in Thailand’s industrial zones means that inlet filters may load faster than European manufacturer baselines predict. Engineers should monitor inlet filter differential pressure in the first months of operation to establish actual replacement intervals for the local environment, rather than relying solely on time-based schedules from the manual.

Q6: Does AERZEN’s rental equipment come pre-verified for particulate class? A: AERZEN rental units are maintained to factory specification. For projects where point-of-use ISO 8573-4 verification is required as part of commissioning or quality documentation, the AERZEN technical team can advise on the testing protocol and connect customers with accredited testing services.

References

1. ISO 8573-1:2010 — Compressed air — Part 1: Contaminants and purity classes — iso.org/standard/46418.html
2. ISO 8573-4:2019 — Compressed air — Part 4: Test methods for solid particle content — iso.org/standard/75575.html
3. ISO 8573-2:2018 — Compressed air — Part 2: Test methods for oil aerosol content — iso.org/standard/69828.html
4. CAGI — Compressed Air and Gas Institute technical resources — cagi.org

Speak to the AERZEN Engineering Team

Whether you are specifying a new compressed air system, verifying compliance with ISO 8573-4, or evaluating whether a rental solution fits your particulate class requirements — the AERZEN Rental Thailand engineering team is ready to assist.

• Office: 038-015-488
• 24/7 Hotline: 098-323-2626
• Email: thai@aerzenrental.com
• Website: www.aerzenrentalth.com

Rent a solution. Expect performance.

About the Author

By Paradorn Wannasung · Master’s in Marketing Communication · AERZEN Rental Thailand

Paradorn Wannasung specialises in technical communication for the industrial compressed air sector. Drawing on AERZEN’s 160-year engineering heritage — from the company’s founding in Germany in 1864 through to current deployments across Southeast Asia’s industrial landscape — Paradorn translates compressed air standards and engineering specifications into accessible guidance for engineers and procurement professionals working in Thai industry.

เขียนโดย Paradorn Wannasung · Master’s in Marketing Communication · AERZEN Rental Thailand

Person JSON-LD

{
  "@context": "https://schema.org",
  "@type": "Article",
  "headline": "ISO 8573-4 Particulate Matter Classes — Solid Contamination Control in Compressed Air",
  "inLanguage": "en",
  "datePublished": "2026-06-20",
  "author": {
    "@type": "Person",
    "name": "Paradorn Wannasung",
    "jobTitle": "Marketing Communication Specialist",
    "alumniOf": {
      "@type": "EducationalOrganization",
      "name": "Master's in Marketing Communication"
    },
    "worksFor": {
      "@type": "Organization",
      "name": "AERZEN Rental Thailand",
      "url": "https://www.aerzenrentalth.com/"
    }
  },
  "publisher": {
    "@type": "Organization",
    "name": "AERZEN Rental Thailand",
    "url": "https://www.aerzenrentalth.com/",
    "foundingDate": "1864",
    "description": "Oil-free blower and compressor rental — ISO 8573-1 Class 0"
  }
}

Visual Brief

• Image concept: Optical particle counter instrument in a compressed air test setup, displayed alongside a class table graphic; navy/gold data visualization aesthetic
• Alt text: “Optical particle counter instrument used for ISO 8573-4 solid particulate testing in a compressed air distribution system”
• Secondary image: ISO 8573-1 particulate class table rendered as a clean infographic with AERZEN navy/gold palette, showing particle size bands and count limits