What is ISO 14644?
ISO 14644 is the international standard governing cleanroom classification, monitoring, and operation. Part 1 defines the classification system based on airborne particulate counts; Part 2 specifies performance test methods and frequencies.
The ISO Class Table
Each ISO class represents a maximum allowable concentration of particles per cubic meter. The most commonly encountered classes in healthcare and pharma:
- ISO 5: ≤3,520 particles ≥0.5 µm/m³ — required for PECs in USP 797 compounding.
- ISO 7: ≤352,000 particles ≥0.5 µm/m³ — Buffer room standard for sterile compounding.
- ISO 8: ≤3,520,000 particles ≥0.5 µm/m³ — Ante-room standard under many state board requirements.
At-Rest vs. Operational Classification
ISO 14644-1 distinguishes between two states: at-rest (no personnel, minimal activity) and operational (normal compounding/manufacturing activity). Both states must meet the specified particle limits. USP 797 requires testing in both states.
How Testing Works
Particle counts are taken at multiple sampling locations using a calibrated laser particle counter. The number of locations, sample volume, and statistical method are all specified in ISO 14644-1 Annex B. Results are analyzed using the 95% Upper Confidence Limit (UCL) method.
How Often Must Classification Be Repeated?
ISO 14644-2 recommends re-testing at intervals not exceeding:
- 6 months for ISO Class 5 and cleaner.
- 12 months for ISO Class 6 and above.
Additionally, re-classification is triggered by any significant change to the HVAC system, facility layout, or manufacturing process.
Common Pitfalls
- Using an out-of-calibration particle counter.
- Sampling in at-rest conditions only (skipping operational testing).
- Insufficient sample volume at each location.
- Not testing after HEPA filter replacement or HVAC modifications.