ISO 14644-1 is the international standard that classifies air cleanliness by particle concentration. For data centres, Class 8 is the common target. Here is what it means and how it is measured.
What ISO 14644-1 measures
The standard classifies cleanrooms and controlled environments by the maximum number of airborne particles per cubic metre of air, at defined sizes between 0.1 and 5 µm. Classes run from ISO Class 1 (cleanest) to ISO Class 9.
The Class 8 limits
Class 8 is the pragmatic target for data halls: clean enough to protect equipment without the cost of a pharmaceutical cleanroom. The limits are:
- 3,520,000 particles ≥ 0.5 µm per m³
- 832,000 particles ≥ 1 µm per m³
- 29,300 particles ≥ 5 µm per m³
How it is verified
Verification uses a calibrated particle counter at representative sample points. The number of points scales with the room area, and the measured concentrations are compared against the class limits.
What it means in practice
Maintaining Class 8 comes down to three things: limiting ingress (sticky mats, filtration), cleaning periodically with HEPA 14 filtration, and working ESD-safely around sensitive equipment. ASHRAE TC 9.9 recommends this level for data centres.
Key takeaways
- Class 8 is the common target for data halls.
- Cleanliness is measured in particles per m³.
- Verification requires a calibrated counter.
- The status is maintained by cleaning plus ingress control.