Key Takeaways
• Cleanroom classification is the global standard for defining the level of cleanliness in a controlled environment, primarily governed by ISO 14644-1.
• The ISO scale ranges from ISO 1 (the cleanest, used in ultra-precision manufacturing) to ISO 9 (equivalent to normal room air).
• Classification is determined by measuring the maximum allowable concentration of airborne particles (specifically those ≥ 0.5 µm in size) per cubic meter of air.
• The older US Federal Standard 209E (e.g., “Class 100”, “Class 10,000”) was officially retired in 2001 but remains widely used in industry terminology.
• Achieving a specific ISO class requires precise control over HEPA filtration, air changes per hour (ACH), and strict personnel gowning protocols.
Introduction to Cleanroom Standards
When designing, building, or operating a cleanroom, the most critical question is: How clean does it need to be?
The answer dictates everything from the HVAC system design and the type of wall panels used, to the gowning procedures your staff must follow. To ensure consistency across industries and borders, the International Organization for Standardization (ISO) developed the ISO 14644 series of standards.
Specifically, ISO 14644-1:2015 (Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness by particle concentration) is the definitive global benchmark.
Understanding Particle Sizes
Before diving into the classifications, it’s essential to understand what we are measuring. Cleanrooms are designed to filter out microscopic airborne particles.
To put this into perspective:
• A human hair is roughly 50 to 100 microns (µm) in diameter.
• A grain of sand is about 90 microns.
• A red blood cell is about 5 microns.
• Bacteria range from 0.3 to 10 microns.
Cleanroom classifications are primarily based on measuring particles that are 0.5 microns (µm) and larger.
The ISO 14644-1 Classification Table
The ISO classification system is based on a logarithmic scale. An ISO 5 cleanroom is ten times cleaner than an ISO 6 cleanroom, which is ten times cleaner than an ISO 7 cleanroom, and so on.
Here is the official breakdown of maximum allowable particles per cubic meter (m³) of air:
| ISO Class | ≥ 0.1 µm | ≥ 0.2 µm | ≥ 0.3 µm | ≥ 0.5 µm | ≥ 1.0 µm | ≥ 5.0 µm |
|---|---|---|---|---|---|---|
| ISO 1 | 10 | 2 | – | – | – | – |
| ISO 2 | 100 | 24 | 10 | 4 | – | – |
| ISO 3 | 1,000 | 237 | 102 | 35 | 8 | – |
| ISO 4 | 10,000 | 2,370 | 1,020 | 352 | 83 | – |
| ISO 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | 29 |
| ISO 6 | 1,000,000 | 237,000 | 102,000 | 35,200 | 8,320 | 293 |
| ISO 7 | – | – | – | 352,000 | 83,200 | 2,930 |
| ISO 8 | – | – | – | 3,520,000 | 832,000 | 29,300 |
| ISO 9 | – | – | – | 35,200,000 | 8,320,000 | 293,000 |
Note: ISO 9 is generally considered equivalent to normal, unfiltered room air.
ISO vs. US Federal Standard 209E
If you’ve worked in the industry for a while, you’ve likely heard terms like “Class 100” or “Class 10,000.” These refer to the older US Federal Standard 209E (FED-STD-209E).
Although the US General Services Administration officially canceled FED-STD-209E in 2001 in favor of the international ISO standard, the terminology remains deeply ingrained in the manufacturing vocabulary.
The FED-STD-209E classes were based on the maximum number of particles (≥ 0.5 µm) permitted per cubic foot of air, rather than per cubic meter.
The Conversion Guide:
• ISO 3 = Class 1
• ISO 4 = Class 10
• ISO 5 = Class 100
• ISO 6 = Class 1,000
• ISO 7 = Class 10,000
• ISO 8 = Class 100,000
Industry Applications by ISO Class
Different industries require vastly different levels of cleanliness. Over-specifying your cleanroom (e.g., building an ISO 5 room when ISO 7 is sufficient) will result in massive, unnecessary construction and operational costs.
ISO 3 and ISO 4 (Class 1 and Class 10)
These are ultra-clean environments, representing the pinnacle of contamination control.
- Applications: Semiconductor wafer fabrication, advanced microelectronics, nanotechnology research
- Airflow: 100% ceiling coverage with ULPA filters, unidirectional (laminar) downward airflow
ISO 5 (Class 100)
This is the standard for critical aseptic processes where product sterility is paramount.
- Applications: Pharmaceutical aseptic filling (EU GMP Grade A/B), sterile compounding pharmacies (USP 797), aerospace component assembly
- Airflow: Unidirectional airflow with HEPA filters covering 40–80% of the ceiling
ISO 6 (Class 1,000)
A transitional classification often used as a background environment for ISO 5 zones or for less critical assembly.
- Applications: Medical device assembly, optical manufacturing, lithium-ion battery production
ISO 7 (Class 10,000)
This is the most common cleanroom classification globally. It provides a highly controlled environment without the extreme costs of lower ISO classes.
- Applications: General pharmaceutical manufacturing (EU GMP Grade C), medical device packaging, electronics assembly, cosmetics production
- Airflow: Non-unidirectional (turbulent) airflow, with HEPA filters covering 15–25% of the ceiling
ISO 8 (Class 100,000)
Often used as a buffer zone or for processes that require basic environmental control.
- Applications: Cleanroom gowning rooms (airlocks), plastic injection molding for medical parts, food and beverage packaging
How to Achieve and Maintain Your ISO Class
Building a cleanroom to meet a specific ISO class is only half the battle; maintaining that classification during daily operations is the real challenge.
1. Air Changes Per Hour (ACH)
The primary mechanism for maintaining cleanliness is the volume of filtered air pumped into the room. This is measured in Air Changes Per Hour (ACH).
- ISO 8: 10 – 20 ACH
- ISO 7: 30 – 60 ACH
- ISO 6: 90 – 180 ACH
- ISO 5: 240 – 480 ACH
2. Gowning Protocols
As mentioned in our previous guide, humans are the largest source of contamination. The stricter the ISO class, the more comprehensive the gowning requirements.
3. Environmental Monitoring and Certification
To prove compliance with ISO 14644-1, cleanrooms must undergo regular certification by an independent third party. This involves using particle counters to measure air quality at specific grid locations throughout the room.
- ISO 5 and cleaner: Every 6 months
- ISO 6 to ISO 8: Every 12 months
Conclusion
Understanding the ISO 14644-1 classification system is the foundational step in any cleanroom project. It dictates your HVAC design, construction materials, operational costs, and daily procedures.
If you are unsure which ISO classification your specific process requires, or if you need help designing a facility to meet a strict standard, the engineering team at RVCleans is here to help. We specialize in designing, manufacturing, and installing modular cleanrooms that guarantee compliance from day one.
Frequently Asked Questions (FAQ)
Q: What is the difference between “At-Rest” and “Operational” states?
A: ISO 14644-1 defines three occupancy states for testing:
- As-Built: The cleanroom is complete and running, but no equipment or personnel are present.
- At-Rest: The cleanroom is complete, equipment is installed and running, but no personnel are present.
- Operational: The cleanroom is functioning normally with equipment running and personnel performing their standard duties. Most regulatory bodies require compliance in the Operational state.
Q: Can a cleanroom lose its ISO classification?
A: Yes. A cleanroom can lose its classification if:
- HEPA filters degrade
- HVAC systems fail to maintain proper pressure
- Personnel do not follow gowning protocols
This leads to higher particle counts and failure in certification tests.
Q: Do I need an ISO 5 cleanroom for food packaging?
A: Generally, no. Most food and beverage packaging facilities operate safely within ISO 7 or ISO 8 environments, focusing more on sanitation and temperature/humidity control rather than ultra-low particle levels.
Need Professional Help?
For professional cleanroom design, manufacturing, and installation services, contact the engineering team at RVCleans.