Cleanroom classification under ISO 14644-1 defines how many airborne particles of a given size are allowed per cubic meter of air, so a cleaner room has a lower class number: Class 5 permits at most 3,520 particles of 0.5 micrometer or larger per m³, while Class 8 permits up to 3,520,000. The standard replaced the older Federal Standard 209E and is the global language for semiconductor, pharmaceutical, medical, and food cleanrooms, tying design, filtration, and testing to a single particle-count scale.
The ISO 14644-1 Particle Limits
The standard sets a maximum concentration formula C_n = 10^n × (0.1/D)^{2.08}, where n is the class number and D is particle size in micrometers. In plain terms, each step down in class halves the allowed particle count. At 0.5 micrometer, Class 8 allows 3,520,000 particles/m³, Class 7 allows 352,000, Class 6 allows 35,200, Class 5 allows 3,520, and Class 4 allows 352. The limits are defined from 0.1 micrometer up to 5 micrometers, and rooms are classified at the sizes relevant to their process. This metric basis makes comparison across industries and countries consistent.
How Cleanrooms Achieve a Class
A room reaches its class through a combination of HEPA or ULPA filtration, unidirectional or turbulent airflow, and pressure cascade. HEPA filters at 99.97 percent efficiency at 0.3 micrometer supply the clean air, and ULPA filters at 99.9995 percent serve Class 3 to 5 zones. Air changes range from 10 to 20 per hour for Class 8, 30 to 60 for Class 7, and 240 to 600 for Class 5 unidirectional flow. A positive pressure of 10 to 15 Pa holds out contamination from adjacent spaces, and gowning and material airlocks maintain the state.
ISO Class Comparison
| ISO class | Particles 0.5 micrometer per m³ | Air changes per hour | Typical use |
|---|---|---|---|
| ISO Class 8 | 3,520,000 | 10 to 20 | General assembly, packaging |
| ISO Class 7 | 352,000 | 30 to 60 | Pharma, optics, medical device |
| ISO Class 6 | 35,200 | 70 to 160 | Injection molding, biotech |
| ISO Class 5 | 3,520 | 240 to 600 (unidirectional) | Filling, semiconductor, surgery |
The table links class to both particle count and the ventilation intensity needed, which drives fan and filter selection.
Key Numbers and Monitoring
Three numbers anchor any cleanroom program. First, the particle limit at the controlling size, for example 3,520 per m³ at 0.5 micrometer for Class 5. Second, the pressure differential, usually 10 to 15 Pa between clean and less-clean zones. Third, the air-change rate, from 10 per hour in Class 8 up to 600 in unidirectional Class 5 flows. Monitoring places particle counters at 2 to 6 points per 30 m³ of space per the standard's sampling table, and recertification happens every 6 to 12 months for Classes 5 to 8 depending on risk.
When to Choose Each Class
- Choose ISO Class 8 for non-critical assembly, packaging, and warehouses where traces of dust are tolerable.
- Choose ISO Class 7 for pharmaceutical compounding, optics, and medical-device work needing low bioburden.
- Choose ISO Class 5 unidirectional flow for aseptic filling, semiconductor exposure, and operating theatres.
- Choose ISO Class 4 or better only for lithography and nanotechnology where sub-micron control is critical.
- Choose turbulent flow with HEPA for lower classes and unidirectional ULPA flow for Class 5 and cleaner.
Testing and Certification
Certification follows ISO 14644-1 and 14644-2: after cleaning and equilibration, a calibrated laser particle counter samples at the required number of locations, often 2 to 6 per 30 m³, while airflow velocity, uniformity, and pressure differential of 10 to 15 Pa are recorded. A room passes only if every sample is at or below the class limit. Continuous monitoring then tracks the state, and a full recertification is scheduled every 6 to 12 months. Filtration, gowning discipline, and pressure cascade together must hold the count, or the class is lost within minutes of a breach.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
Airflow, Filtration, and Pressurization
Achieving a class depends on moving enough filtered air and keeping contamination out. Unidirectional Class 5 flow uses ceiling HEPA or ULPA filters at 99.97 or 99.9995 percent efficiency and runs 240 to 600 air changes per hour so the sweep velocity is 0.3 to 0.45 m/s across the work plane. Turbulent Class 7 or 8 rooms use 30 to 60 or 10 to 20 air changes with HEPA supply and recirculation. A positive pressure of 10 to 15 Pa holds the clean side above adjacent spaces, and airlocks with interlocked doors stop bursts of contamination during entry. Gowning, wiped tools, and isolated process exhaust keep the particle count at the limit, which for Class 5 is 3,520 per m³ at 0.5 micrometer and for Class 8 is 3,520,000.
Monitoring, Gowning, and Recertification
Continuous particle counters at 2 to 6 points per 30 m³ watch the state, and an alert triggers when any size exceeds the class for a sustained period. Personnel follow a graded gowning ladder, from smocks in Class 8 to full bunny suits in Class 5, because a single operator sheds 100,000 to 1,000,000 particles per minute without control. Recertification per ISO 14644-1 and 14644-2 happens every 6 to 12 months for Classes 5 to 8, with a fresh laser count at rest and records of airflow and pressure. Between tests, disciplined behavior and intact filters hold the count; a torn HEPA or a propped airlock can breach Class 5 within minutes, so the monitoring and the documented procedure are what keep the room certified day to day.
Particle Counting and Alerts
Portable counters used at commissioning follow the ISO 14644-1 location table of 2 to 6 points per 30 m³, while fixed counters give live trending. An alert set at 70 to 90 percent of the class limit lets staff react before a breach; for Class 5 that means watching the 0.5 micrometer count approach 3,000 per m³, well under the 3,520 limit, to keep margin for process upset.
FAQ
What does ISO 14644-1 Class 5 mean?
ISO 14644-1 Class 5 allows at most 3,520 particles of 0.5 micrometer or larger per cubic meter of air, a level typical of pharmaceutical filling and semiconductor lines. It is stricter than Class 7, which allows 352,000 such particles, and is achieved with HEPA or ULPA filtration and tight airflow control.
How many particles are allowed in each ISO class?
Particle limits double roughly with each class step: Class 8 permits 3,520,000 particles at 0.5 micrometer per m³, Class 7 allows 352,000, Class 6 allows 35,200, Class 5 allows 3,520, and Class 4 allows 352. Each class is defined at several particle sizes from 0.1 to 5 micrometers.
What is the difference between Federal Standard 209E and ISO 14644-1?
Federal Standard 209E used named classes such as Class 100, Class 1,000, and Class 10,000, while ISO 14644-1 uses Class 5, Class 7, and Class 8 with a metric particle count. Class 100 roughly equals ISO Class 5, Class 1,000 equals Class 7, and Class 10,000 equals Class 8; 209E was withdrawn in 2001.
How is a cleanroom tested and certified?
Certification counts particles at rest using a laser counter at set locations, often 2 to 6 points per 30 m³ or per ISO 14644-1 Annex B table, after the room is cleaned and running. Recertification is typically every 6 to 12 months for Class 5 to 8, and airflow and pressure differential of 10 to 15 Pa are verified.