Clean room classification is the way a controlled room is ranked by how many airborne particles each cubic metre of its air may contain. The room is given filtered supply air, pressure differences against its neighbours and limited access for people and materials, but its rank is earned by counting particles, not by pointing at the drawings. In pharmaceutical manufacturing two ranking systems are used side by side: the ISO 14644-1 classes that apply across many industries, and the grades A to D set out in Annex 1 of the EU GMP guide for sterile medicines.
Two systems: ISO classes and GMP grades
The US Food and Drug Administration’s guidance on aseptic processing describes ISO 14644-1 designations as providing uniform particle concentration values for cleanrooms in multiple industries. Annex 1 of EudraLex Volume 4, revised in 2022 and fully applicable since 25 August 2024, points to the ISO 14644 series for qualifying cleanrooms and to ISO 14644-1 for the minimum number and position of sampling locations. Its grades, however, are defined in its own terms, with separate limits for a room at rest and in operation, and with microbial limits alongside the particle counts.
What the four grades mean
Annex 1 describes four grades of cleanroom or zone for sterile manufacture:
- Grade A: the critical zone for high-risk operations, such as the filling zone, open primary packaging or making aseptic connections. It is normally provided by unidirectional airflow within barrier systems or isolators.
- Grade B: the background cleanroom for grade A during aseptic preparation and filling, where grade A is not an isolator.
- Grades C and D: cleanrooms for less critical stages in making aseptically filled sterile products, or backgrounds for isolators. They can also be used to prepare and fill terminally sterilised products.
Particle limits for classification
For classification, Annex 1 requires counting total particles of 0.5 µm and larger and of 5 µm and larger, both at rest and in simulated operations, against the limits in its Table 1 (particles per cubic metre):
| Grade | ≥0.5 µm at rest | ≥0.5 µm in operation | ≥5 µm at rest | ≥5 µm in operation |
|---|---|---|---|---|
| A | 3,520 | 3,520 | Not specified | Not specified |
| B | 3,520 | 352,000 | Not specified | 2,930 |
| C | 352,000 | 3,520,000 | 2,930 | 29,300 |
| D | 3,520,000 | Not predetermined | 29,300 | Not predetermined |
For grade D the manufacturer sets its own in-operation limits based on a risk assessment and routine data. Classification is also separate from routine monitoring, which uses its own maximum action limits for total particles (Table 5) and for viable particles (Table 6).
At rest versus in operation
“At rest” describes the room without normal production activity; “in operation” describes it while work, or a simulation of that work, is going on. The table shows why the distinction matters: grade B allows 3,520 particles of 0.5 µm per cubic metre at rest but 352,000 in operation, and grade C moves from 352,000 to 3,520,000. Annex 1 asks that appropriate cleanliness levels be maintained in both states. Grade A is the exception, with the same limit in both states, because it is the critical zone.
Rough ISO equivalents
Comparing only the 0.5 µm figures with the ISO designations listed in the FDA guidance (ISO 5 = 3,520, ISO 7 = 352,000 and ISO 8 = 3,520,000 particles per cubic metre) gives this approximate mapping:
| EU GMP grade | At rest (0.5 µm) | In operation (0.5 µm) |
|---|---|---|
| A | about ISO 5 | about ISO 5 |
| B | about ISO 5 | about ISO 7 |
| C | about ISO 7 | about ISO 8 |
| D | about ISO 8 | Set by the manufacturer |
The FDA guidance itself says an ISO 5 concentration approximately equals EU grade A. The word approximately matters: a GMP grade also carries 5 µm limits, microbial limits and state-specific requirements that an ISO class number alone does not.
Classification is measured, and repeated
Annex 1 treats classification as one part of cleanroom qualification, assessed by measuring total particle concentration. It also requires periodic requalification, which at a minimum includes classification, integrity testing of final filters, airflow volume measurement and verification of pressure differences between rooms. Adjacent rooms of different grades should have a pressure difference of at least 10 pascals, given as a guidance value.
What it means for medical cannabis processing
Annex 1 is written for sterile products, but it states that some of its principles, including cleanroom classification, may be used to support the manufacture of products not intended to be sterile where control of microbial and particle contamination is important. A manufacturer that chooses to do this should document which principles it applies and accept that compliance with them has to be demonstrated.
For non-sterile manufacture, the general GMP rules ask for production areas to be effectively ventilated, with air control including filtration where necessary, appropriate to the products and operations. The herbal annex adds that sampling, weighing, mixing and processing of herbal substances need specific provisions whenever dust is generated, such as dust extraction or dedicated premises, and that equipment and filters used in extraction must be compatible with the extraction solvent. The general guide also names the packaging of dry products as a dust-generating step that needs measures against cross-contamination.
So for a flower packing room or an extraction suite, these texts do not by themselves name a required A to D grade. If a manufacturer chooses to work to one, the choice, its limits and its monitoring plan need to be documented and justified, and the room must actually be classified by measurement. Whether that approach is acceptable is decided by the inspecting authority, not by the facility designer.
Common mistakes
- Saying “ISO 7 equals grade C”. That holds only at rest. In operation grade C allows the ISO 8 figure, while grade B in operation matches ISO 7.
- Quoting a limit without its state. A number without “at rest” or “in operation” is incomplete.
- Assuming filters make a cleanroom. The grade is shown by classification tests and requalification, not by an equipment list.
- Confusing classification with monitoring. Classification qualifies the room; routine monitoring uses separate action limits.
- Ignoring the 5 µm and microbial limits. They are part of a GMP grade even when the 0.5 µm count passes.
Before designing or buying against a grade, read the current Annex 1 and ask the authority that will inspect the site how it expects the choice to be justified.