ISO 14644-1 Cleanroom Classification: Particle Count Limits & How to Verify Them
A cleanroom’s ISO class is not a design claim; it is a measured result, verified with a calibrated particle counter following ISO 14644-1. A failed classification can delay a facility opening or trigger an audit finding, so the limits and the procedure deserve attention.
This guide covers what ISO 14644-1 defines, the ISO Class 1–9 particle count limits, the sampling rules, and how a portable six-channel counter such as the CSJ-D2 verifies a cleanroom class on site.
What ISO 14644-1 Defines
ISO 14644-1:2015, the first part of the ISO 14644 series, defines nine cleanroom classes by the maximum permitted concentration of airborne particles equal to or larger than a stated size, expressed in particles per cubic metre (particles/m³).
- **The limits follow a formula.** For particle size D, the concentration limit is Cn = 10^N × (0.1/D)^2.08, where N is the class number; the table below gives the rounded values.
- **The scope is particles from 0.1 µm to 5 µm.** Air changes, pressure differentials, temperature, and humidity are handled elsewhere in the ISO 14644 series and in guidance such as EU GMP Annex 1.
The ISO 14644-1 Classification Table (ISO Class 1–9)
The table below gives the maximum permitted concentrations (particles/m³) per ISO class and particle size, from ISO 14644-1:2015 Table 1. A dash means no limit is specified for that combination.
| ISO Class | ≥0.1 µm | ≥0.2 µm | ≥0.3 µm | ≥0.5 µm | ≥1 µm | ≥5 µm |
|———–|———|———|———|———|——-|——-|
| ISO Class 1 | 10 | 2 | — | — | — | — |
| ISO Class 2 | 100 | 24 | 10 | 4 | — | — |
| ISO Class 3 | 1,000 | 237 | 102 | 35 | 8 | — |
| ISO Class 4 | 10,000 | 2,370 | 1,020 | 352 | 83 | — |
| ISO Class 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | 29 |
| ISO Class 6 | 1,000,000 | 237,000 | 102,000 | 35,200 | 8,320 | 293 |
| ISO Class 7 | — | — | — | 352,000 | 83,200 | 2,930 |
| ISO Class 8 | — | — | — | 3,520,000 | 832,000 | 29,300 |
| ISO Class 9 | — | — | — | 35,200,000 | 8,320,000 | 293,000 |
Reading the Table: 0.3 µm, 0.5 µm, and 5 µm
Most classification work happens at three sizes:
- **≥0.5 µm** is the reference size for most pharmaceutical cleanrooms. An ISO Class 5 room must not exceed **3,520 particles/m³ at ≥0.5 µm** — the limit EU GMP Annex 1 sets for Grade A areas in operation.
- **≥0.3 µm** is measured where finer contamination control is needed; it is the smallest size many portable counters can resolve — including the CSJ-D2, with its 0.3 µm sensitivity. ISO Class 5 at ≥0.3 µm is 10,200 particles/m³.
- **≥5 µm** captures large particles relevant to sterile manufacturing: ISO Class 5 allows 29 particles/m³, ISO Class 7 allows 2,930, and ISO Class 8 allows 29,300.
Two pitfalls: the limits are per cubic metre (per-cubic-foot data from the withdrawn Federal Standard 209E cannot be compared directly), and the ≥ sign covers every particle at or above the stated size.
Sampling Rules in ISO 14644-1
The standard specifies how many locations to sample and how much air to draw at each one (Annex A of the 2015 edition).
Number of Sampling Locations
The minimum number of locations is the square root of the room area in square metres, rounded up, with a minimum of one and a maximum of 500:
- 10 m² → 4 locations
- 20 m² → 5 locations
- 100 m² → 10 locations
- 400 m² → 20 locations
Minimum Sample Volume and Time
At each location, the minimum sample volume is Vs = (20 / Cn,m) × 1,000 litres, where Cn,m is the class limit for the largest particle size considered. The sample must be at least 2 litres and 1 minute and may be split into portions meeting those minimums.
Practical examples at 2.83 L/min (0.1 CFM):
- **ISO Class 5, largest size 0.5 µm:** Vs = 5.68 L → about 2 minutes per location.
- **ISO Class 7, largest size 5 µm:** Vs = 6.8 L → about 2.4 minutes per location.
- **ISO Class 8, largest size 5 µm:** Vs = 0.68 L, so the 2 L minimum applies → 1 minute per location.
How a Portable 2.83 L/min Counter Is Used for Classification
A portable counter is the practical tool for classifying ISO Class 5 and above — the range covering pharmaceutical cleanrooms and hospitals:
- **Configure** the counter for the target class and state and select the channels (commonly 0.3, 0.5, and 5.0 µm).
- **Set the sample time** per location so the required volume is drawn, or let the auto-classification routine calculate it.
- **Sample the grid** of locations at working height, then **review the results** and confirm or reject the class on the spot.
- **Compare per-location averages.** The 2015 edition dropped the 95% upper confidence limit calculation of the 1999 edition; each location’s average is compared directly with the class limit.
- **One location over the limit fails the class.** If any location’s average exceeds the limit, the room does not meet that class.
- **State the state.** At-rest and operational results can differ by orders of magnitude; certificates should record the state, sizes measured, and the counter and calibration used.
- **Classification is a snapshot.** It proves compliance at the moment of testing; continuous assurance comes from monitoring under ISO 14644-2 or the Annex 1 contamination control strategy.
- Construction, renovation, or relocation of the cleanroom
- Major changes to HVAC, filtration, or pressurization
- A contamination incident, failed excursion, or failed monitoring
- A change of use (for example, ISO 8 re-rated as ISO 7)
The GCC-CSJ-D2 Laser Airborne Particle Counter fits this workflow directly: six channels spanning 0.3–10 µm, 2.83 L/min sampling flow, 0.3 µm sensitivity, 246-group storage, and a built-in thermal printer. A 20 m² ISO Class 5 room (five locations, about two minutes each) can be sampled, evaluated, and documented in one visit, with printed records for the auditor. Its automatic evaluation covers ISO 14644-1 and Federal Standard 209E.
Interpreting the Results
When to Reclassify
ISO 14644-2:2015 sets a maximum interval of 12 months between classifications, with more frequent testing when a risk assessment calls for it. Reclassify sooner after any event that could change air cleanliness:
Conclusion
ISO 14644-1 classification is a measurement discipline: a class is only as credible as the counter, the sampling procedure, and the documentation behind it. A portable instrument with 0.3 µm sensitivity, six channels, and built-in ISO evaluation removes the practical friction — exactly what the CSJ-D2 laser particle counter was designed for. For help selecting a counter or planning a qualification, talk to GCC Cleanswan, a supplier of environmental monitoring instruments for pharmaceutical GMP laboratories, cleanrooms, hospitals, and research institutions, with more than 20 years of controlled-environment experience.
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Frequently Asked Questions
What are the ISO 14644-1 particle limits for ISO Class 5?
ISO Class 5 allows 3,520 particles/m3 at >=0.5 um and 29 particles/m3 at >=5 um.
How many sampling locations do I need?
Per ISO 14644-1, the minimum number of locations is the square root of the room area in m2. For example, a 100 m2 room needs at least 10 locations.
How long does classification sampling take?
Each location requires a minimum sample volume (2 L or 20/Cn,m x 1000 L, whichever is larger). At 2.83 L/min a 1,000 L sample takes about 6 hours; at 100 L/min it takes about 10 minutes.
How often must a cleanroom be reclassified?
ISO 14644-2 recommends particle count verification every 6-12 months, with the interval justified by risk. Reclassification is also required after major changes to the facility or HVAC system.