ISO cleanroom classifications provide a standardized way to define and verify airborne particle cleanliness. Understanding the applicable class helps facility teams establish performance criteria, evaluate cleanroom conditions, and support product and process requirements.
Cleanrooms are used across pharmaceuticals, biotechnology, medical devices, electronics, aerospace, and other industries where airborne contamination can affect product quality, process performance, or research.
The ISO 14644 family addresses several aspects of cleanroom control, including particle classification, monitoring, test methods, design and construction, and operations. ISO 14644-1 provides the framework used to classify air cleanliness by airborne particle concentration.
ISO 14644-1 defines ISO Classes 1 through 9 based on the maximum permitted concentration of airborne particles at specified particle sizes. ISO Class 1 is the most stringent; as the class number increases, the permitted particle concentration increases. Classification is established for a specified occupancy state, such as as-built, at-rest, or operational.
ISO Cleanroom Classifications: Classes 1–9
The examples below use selected particle sizes from ISO 14644-1. Limits are expressed as the maximum permitted number of particles per cubic meter of air at or above the stated particle size.
ISO Class 1
ISO Class 1 is the most stringent ISO air-cleanliness class. The maximum permitted concentration at ≥0.1 µm is 10 particles/m³. It is used only for highly contamination-sensitive applications.
ISO Class 2
ISO Class 2 permits up to 100 particles/m³ at ≥0.1 µm and 10 particles/m³ at ≥0.3 µm. It supports specialized processes requiring extremely low airborne particle concentrations.
ISO Class 3
ISO Class 3 permits up to 102 particles/m³ at ≥0.3 µm and 35 particles/m³ at ≥0.5 µm. The appropriate use of this class depends on the contamination sensitivity of the product or process.
ISO Class 4
ISO Class 4 permits up to 1,020 particles/m³ at ≥0.3 µm and 352 particles/m³ at ≥0.5 µm. It may be specified for high-cleanliness manufacturing, research, or processing applications.
ISO Class 5
ISO Class 5 permits up to 3,520 particles/m³ at ≥0.5 µm and 832 particles/m³ at ≥1.0 µm. ISO Class 5 environments are widely used for critical zones in aseptic processing and sterile compounding, where additional regulatory and contamination-control requirements may also apply.
ISO Class 6
ISO Class 6 permits up to 35,200 particles/m³ at ≥0.5 µm and 293 particles/m³ at ≥5.0 µm. It may be used for controlled manufacturing or processing where this level of airborne particle control is appropriate.
ISO Class 7
ISO Class 7 permits up to 352,000 particles/m³ at ≥0.5 µm and 2,930 particles/m³ at ≥5.0 µm. It is commonly used for controlled processing spaces and as a background environment supporting cleaner critical zones, depending on the application.
ISO Class 8
ISO Class 8 permits up to 3,520,000 particles/m³ at ≥0.5 µm and 29,300 particles/m³ at ≥5.0 µm. It is often used for controlled support, manufacturing, staging, or gowning spaces when the process does not require a cleaner classification.
ISO Class 9
ISO Class 9 is the least stringent class in ISO 14644-1. It permits up to 35,200,000 particles/m³ at ≥0.5 µm and 293,000 particles/m³ at ≥5.0 µm. Although it is sometimes compared with ordinary room air, an uncontrolled space should not be assumed to meet ISO Class 9 without measurement.
Achieving an ISO class is only one part of operating a cleanroom. The engineering and operational controls needed to maintain that cleanliness depend on the room’s intended use, process risk, facility design, and any applicable industry or regulatory requirements.
Common cleanroom control considerations include:
- HEPA or ULPA filtration, as appropriate for the application
- Airflow volume and room air exchange rates
- Room differential pressures and directional airflow
- Unidirectional or non-unidirectional airflow design
- Cleanable, compatible room and equipment materials
- Personnel gowning and behavior
- Personnel entry and exit procedures
- Material transfer procedures
- Cleaning and disinfection procedures, as applicable
ISO 14644-2 addresses monitoring plans related to particle concentration, while ISO 14644-5:2025 covers operational controls including personnel, material transfer, cleaning, maintenance, and monitoring. Programs should reflect intended use and applicable requirements.
Cleanroom Testing and Certification Services from TSS
- Technical Safety Services (TSS) provides cleanroom testing and certification for controlled environments across regulated and high-technology industries. Testing can be aligned with ISO 14644, facility specifications, and applicable industry requirements.
Cleanroom testing services may include:
- Nonviable Particle Counting: Measures airborne particle concentrations to verify the specified ISO cleanliness classification.
- HEPA Filter Integrity Testing: Uses an aerosol challenge to identify filter-media defects and bypass leakage and to verify proper filter installation.
- Room Performance Testing: Measures airflow volume, air exchange rate, differential pressure, temperature, and relative humidity against applicable criteria.
- Environmental Monitoring and Documentation: Viable monitoring and documented test results can support quality systems, trending, audits, and regulatory requirements.
To take advantage of our cleanroom testing services, please contact us today.
