Cleanroom Airborne Particle Classification
Determining airborne-particle concentration at defined sampling locations, under a stated occupancy state, for the selected cleanliness class and particle-size threshold — and choosing an instrument that can actually resolve it.
Classification Requirements and Particle-Size Thresholds
Classification answers one question: at the selected particle size, does the airborne concentration at the defined sampling locations meet the limit for the selected class, in the stated occupancy state? The sampling plan, instrument configuration, measurement sequence and reporting method all follow from that requirement.
Classification Plan Inputs
- Cleanliness classSet by the process requirement, not by the instrument available.
- Particle-size thresholdThe standard addresses thresholds from 0.1 µm to 5 µm. The chosen threshold drives everything downstream.
- Occupancy stateAs-built, at-rest and operational are recognised, distinct conditions and are not interchangeable.
- Sampling locationsDistributed across the area, with additional weight where exposure risk is highest.
- Sample volumeSufficient volume at each location for the concentration being measured.
- Instrument capabilityMinimum resolvable size and sample flow adequate for the threshold and the concentration.
Governing references
ISO 14644-1Classification of air cleanliness by airborne particle concentration ISO 21501-4Performance and calibration of light-scattering airborne particle countersISO 21501-4 governs the measurement instrument; ISO 14644-1 governs the cleanroom classification. They are frequently cited together and are not interchangeable.
Cleanroom Classification Measurement Method
A light-scattering optical particle counter draws a known air volume through a laser beam and sizes each particle by the light it scatters. Counts accumulate into cumulative size channels, which is why a result is always stated as “at or above” a threshold size.
At low airborne-particle concentrations, higher sample flow can reduce the time required to collect the specified sample volume. Instrument selection must nevertheless balance minimum measurable particle size, concentration range, sample flow and the requirements of the classification plan.
ISO 14644-1 particle concentration reference
Maximum cumulative concentrations in particles/m³ for particles equal to or larger than each stated size. The six threshold sizes are shown in micrometres (µm); a dash means that ISO 14644-1 does not specify a classification limit for that class-and-size combination.
| ISO Class | ≥0.1 µm | ≥0.2 µm | ≥0.3 µm | ≥0.5 µm | ≥1 µm | ≥5 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 |
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“—” indicates that no classification concentration is specified for the selected class and particle-size combination. It does not mean zero particles. In the standard these cells carry notes explaining that a limit is inappropriate either because the concentration is too low for meaningful sampling, or too high for the measurement method.
Instrument capability alone does not establish an ISO cleanliness class. Classification also depends on particle size, sampling locations, sample volume, occupancy state, measurement plan and applicable project specification.
Ultra-clean measurement at 0.1 µm
Semiconductor facilities can require extremely low airborne-particle concentrations, with measurement strategy determined by process sensitivity, selected cleanliness class, particle-size threshold and facility contamination-control requirements.
Where the governing requirement sets a 0.1 µm threshold, the instrument itself must resolve that size — no amount of sampling time compensates for an instrument whose smallest channel is larger than the threshold being claimed.
Kanomax 3950 — 0.1 µm Particle Measurement
A two-channel optical particle counter measuring at 0.1 µm and 0.3 µm with a 2.83 L/min sample flow, with particle-counter performance according to ISO 21501-4 and JIS B9921, and Ethernet, RS-485 and USB interfaces for integration into fab monitoring networks.
Kanomax specifies it for measurement in ultra-clean semiconductor environments. Instrument capability is one input to a classification; the class itself is established by the classification plan and the method, not by the counter alone.
View the Kanomax 3950 →Equipment suitability
ISO 14644-14 · 2026 (Edition 2) — Assessment of suitability for use of equipment by airborne particle concentration.
Use this reference when assessing machinery, measurement equipment, tools and process equipment introduced into a cleanroom. Whether an item is suitable for use in an environment of a given cleanliness is a different question from classifying the room, and this reference does not belong in the class-limit table above.
Semiconductor Contamination-Control Attributes
The applicable reference follows the failure mechanism. Airborne particle class should not be used as a substitute for nanoscale-particle monitoring, airborne molecular contamination, surface cleanliness, deposition or equipment-emission assessment.
| Contamination attribute | Reference | Engineering role |
|---|---|---|
| Airborne particles, 0.1–5 µm | ISO 14644-1:2015 | Classification by cumulative airborne-particle concentration. |
| Nanoscale particles | ISO 14644-12:2018 | Monitoring air cleanliness at a lower size limit of 0.1 µm or below, mainly in operation. |
| Airborne chemical contamination | ISO 14644-8:2022 | Assessment of air cleanliness by chemical concentration where chemicals are a process risk. |
| Surface particles | ISO 14644-9:2022 | Assessment of particle cleanliness on solid surfaces. |
| Surface chemical contamination | ISO 14644-10:2022 | Assessment of chemical compounds or elements on solid surfaces. |
| Particle deposition | ISO 14644-17:2021 | Application and interpretation of particle-deposition-rate evidence on vulnerable surfaces. |
| Equipment and materials | ISO 14644-14:2026 / -15:2026 | Suitability by airborne particle concentration and airborne chemical concentration. |
| Cleanroom-surface cleaning | ISO 14644-13:2026 | Guidance for cleaning surfaces to specified particle and chemical cleanliness levels. |
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Ultra-Clean Particle Measurement Routes
| Requirement | Technology route |
|---|---|
| 0.1 µm | Kanomax 3950 View product → |
| High-flow 0.3 µm | Kanomax 3905 / 3910 View products → |
| High-flow 0.5 µm | Kanomax 3920 View product → |
| Portable spot verification | Kanomax 3888 / 3889 View products → |
| Integrated cleanroom measurement | Topas CPA 341 View product → |
| Continuous monitoring | Kanomax remote sensors View products → |
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Graded-area classification
Sterile-manufacturing environments combine cleanroom classification with facility-specific qualification and requalification requirements. Classification of the graded area is one input to that programme, performed in the occupancy state the applicable guidance specifies and repeated at the interval the facility's contamination control strategy sets.
The approved protocol, sampling locations, occupancy state, data review and acceptance remain within the facility's pharmaceutical quality system and contamination control strategy.
Pharmaceutical priorities →
Grade A, B, C and D airborne-particle limits
For sterile pharmaceutical manufacture in India, revised Schedule M to the Drugs Rules, 1945 defines the Grade A–D particle limits below and requires ISO methodology for cleanroom classification. Formal classification remains distinct from the operational environmental-monitoring programme.
| Schedule M grade | At rest | In operation | ||
|---|---|---|---|---|
| ≥0.5 µm | ≥5.0 µm | ≥0.5 µm | ≥5.0 µm | |
| Grade A | 3,520 | 20 | 3,520 | 20 |
| Grade B | 3,520 | 29 | 352,000 | 2,900 |
| Grade C | 352,000 | 2,900 | 3,520,000 | 29,000 |
| Grade D | 3,520,000 | 29,000 | Not defined | Not defined |
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Regulatory source: CDSCO, Drugs Rules 1945 consolidated through 2024, revised Schedule M →. Confirm the applicable notified text and facility licence conditions for each project.
Standards & regulatory context
| Reference | Edition / status | Role |
|---|---|---|
| ISO 14644-1 | 2015 (Edition 2) — Current published reference | Classification of air cleanliness by airborne particle concentration |
| ISO 21501-4 | 2018 (Edition 2) + Amendment 1:2023 — Current published reference | Performance and calibration context for airborne optical particle counters |
| ISO 14644-14 | 2026 (Edition 2) — Current published second edition | Semiconductor contextual reference — equipment suitability, not a cleanliness class |
| ISO 14644-2 | 2015 (Edition 2) — Current published reference | Risk-based monitoring plan providing evidence of continued cleanroom performance |
| ISO 14644-3 | 2019 (Edition 2) — Current published reference | Cleanroom and clean-zone test methods used in qualification |
| Revised Schedule M | G.S.R. 922(E), 28 December 2023 — Current Indian regulatory requirement | Indian GMP requirements for pharmaceutical manufacturing, including sterile-area classification and monitoring |
| EU GMP Annex 1 | 2022 revision — Current published reference | EU sterile medicinal-product context only; it is not the Indian statutory requirement |
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ISO 21501-4 is not the cleanroom classification standard. It governs the performance and calibration characteristics of the counting instrument. Classification of air cleanliness by airborne particle concentration is the role of ISO 14644-1.
Particle-Counter Selection by Measurement Requirement
Selection is driven by the smallest particle size you must resolve and the sample flow you need to reach the required volume in a workable time.
| Measurement requirement | Technology route |
|---|---|
| 0.1 µm ultra-clean measurement | Kanomax 3950 — 0.1 / 0.3 µm at 2.83 L/min |
| 0.3 µm high-flow portable | Kanomax 3905 / 3910 — 28.3 and 50 L/min |
| 0.5 µm very-high-flow | Kanomax 3920 — 100 L/min |
| Handheld verification | Kanomax 3888 / 3889 — 0.3 µm at 2.83 L/min; 3 channels on the 3888, 6 on the 3889 |
| Qualification ecosystem | Topas CPA 341 — 0.3–10 µm in five size classes at 28.3 L/min |
| Fixed monitoring | Kanomax remote particle sensors — see Continuous Monitoring |
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The 3905, 3910 and 3920 are distinct models and are not interchangeable: the 3905 and 3910 measure from 0.3 µm while the 3920 measures from 0.5 µm, and each runs a different sample flow. Low-flow handheld measurement is a verification and spot-check route, not a universal equivalent to a higher-flow classification method.
3950Ultra-clean 0.1 µm particle measurement for semiconductor cleanrooms.- 0.1 / 0.3 µm
- 2.83 L/min
- Portable
- ISO 21501-4
3900 SeriesPortable high-flow particle-counter family with model-dependent minimum particle size and sample flow.- 3905 — 0.3 µm, 28.3 L/min
- 3910 — 0.3 µm, 50 L/min
- 3920 — 0.5 µm, 100 L/min
- 6 channels · ISO 21501-4
3888 / 3889Portable spot verification and supporting particle measurement where the sampling requirement and instrument capability are appropriate.- 0.3 µm
- 2.83 L/min
- 3 or 6 channels
- Battery
CPA 341Particle measurement across the cleanroom qualification workflow.- 0.3 – 10 µm
- 28.3 L/min
- 5 size classes
- Touchscreen
Cleanroom Classification Measurement Configuration
Share the cleanliness class, the particle-size threshold, the occupancy state, the room area and the applicable project or regulatory reference.