ISO Cleanroom Classifications, Explained
June 14, 2026 · C1D1 Booths Engineering Team
ISO 14644-1 defines nine cleanroom classes based on airborne particle counts. Here's what each class means, how they compare to the old Federal Standard 209E, and when you need a cleanroom vs a C1D1 hazardous location room.
What Is a Cleanroom?
A cleanroom is a controlled environment where airborne particulate contamination is maintained below defined limits. Cleanrooms are used in semiconductor manufacturing, pharmaceutical production, medical device assembly, aerospace component fabrication, and other processes where contamination can cause product defects or safety hazards.
Cleanroom classification is governed by ISO 14644-1, which replaced the older U.S. Federal Standard 209E (FS 209E) in 2001. However, FS 209E terminology (Class 10, Class 100, etc.) is still widely used in industry.
ISO Classification System
ISO 14644-1 classifies cleanrooms from ISO Class 1 (cleanest) to ISO Class 9 (least clean) based on the maximum allowable concentration of airborne particles per cubic meter:
| ISO Class | ≥0.1 µm particles/m³ | ≥0.5 µm particles/m³ | ≥5 µm particles/m³ | FS 209E Equivalent |
|---|---|---|---|---|
| ISO 1 | 10 | — | — | — |
| ISO 2 | 100 | — | — | — |
| ISO 3 | 1,000 | 35 | — | Class 1 |
| ISO 4 | 10,000 | 352 | — | Class 10 |
| ISO 5 | 100,000 | 3,520 | 29 | Class 100 |
| ISO 6 | 1,000,000 | 35,200 | 293 | Class 1,000 |
| ISO 7 | — | 352,000 | 2,930 | Class 10,000 |
| ISO 8 | — | 3,520,000 | 29,300 | Class 100,000 |
| ISO 9 | — | 35,200,000 | 293,000 | Room air |
Common Applications by ISO Class
| ISO Class | Typical Applications |
|---|---|
| ISO 1–3 | Advanced semiconductor fab, nanotechnology research |
| ISO 4–5 | Semiconductor manufacturing, hard disk assembly, pharmaceutical sterile fill/finish |
| ISO 6–7 | Medical device assembly, pharmaceutical manufacturing, aerospace optics |
| ISO 8 | General pharmaceutical production, medical device packaging, food processing |
| ISO 9 | Controlled but not classified — general manufacturing with contamination controls |
HVAC and Air Change Requirements
Achieving and maintaining a cleanroom classification requires careful HVAC design. Higher ISO classes (cleaner) require more air changes per hour (ACH) and higher-efficiency filtration:
| ISO Class | Air Changes/Hour | HEPA/ULPA Coverage |
|---|---|---|
| ISO 5 | 240–480 ACH | ~100% ceiling coverage with HEPA |
| ISO 6 | 150–240 ACH | ~50–60% ceiling coverage |
| ISO 7 | 60–90 ACH | ~25–35% ceiling coverage |
| ISO 8 | 10–25 ACH | Fan filter units or ducted HEPA |
Cleanroom vs C1D1 Room: Key Differences
Cleanrooms and C1D1 hazardous location rooms serve different purposes and are governed by different standards. They are sometimes confused because both involve controlled environments with specialized HVAC:
| Feature | Cleanroom | C1D1 Room |
|---|---|---|
| Primary hazard controlled | Particulate contamination | Flammable vapor/explosion risk |
| Governing standard | ISO 14644-1 | NEC Article 500/501, NFPA 33 |
| Electrical equipment | Standard commercial grade | Explosion-proof (manufacturer-marked for C1D1) |
| Ventilation purpose | Remove particles, maintain pressure | Dilute vapors below LFL |
| Construction | Smooth, non-shedding surfaces | Noncombustible, fire-resistive |
| PE drawings required | Typically not required | Required in most jurisdictions |
Some applications require both cleanroom and C1D1 classification — for example, a pharmaceutical spray coating operation that uses flammable solvents in a contamination-controlled environment. C1D1 Booths can design rooms that meet both sets of requirements simultaneously.
C1D1 Booths Clean Room Products
C1D1 Booths offers ISO 8 modular cleanrooms as a standard product line, with options for ISO 7 configurations. All cleanroom products are constructed from noncombustible materials and can be specified with C1D1 electrical equipment where the process requires it.
Browse our cleanroom product line or configure a custom cleanroom for your application.