Annex 1 grades A, B, C and D: four letters that decide where you may fill a sterile vial, how you gown up to enter the area and how many environmental samples you will take every year. The 2022 revision of EU GMP Annex 1, in operation since 25 August 2023, updated the particle limits of the four grades, moved the Grade A microbial action levels to “no growth” and clarified the relationship with ISO 14644-1 classes. This guide gives you the updated tables, the ISO equivalences, the difference between classification and monitoring, and the mistakes inspectors challenge most often.
Annex 1 grades A, B, C and D: what they define
The grades are the cleanliness levels that Annex 1 assigns to contamination-controlled environments according to the risk of the operations performed in them:
- Grade A: the critical zone for high-risk operations such as aseptic filling, aseptic connections and container closure. It is maintained by unidirectional airflow and, in conventional set-ups, has a Grade B background; with isolators, the Contamination Control Strategy (CCS) may justify a lower-grade background.
- Grade B: the background environment surrounding the Grade A zone for aseptic preparation and filling.
- Grades C and D: areas for less critical stages of sterile manufacturing, such as preparation of solutions to be filtered (C) or washing of components and equipment (D).
The methodological point introduced by the 2022 revision is that grades are not labels on a floor plan: they are an outcome of the site CCS, which must justify where each operation is performed, with which protections and with which monitoring.
Particle limits: the classification table
Classification is performed according to ISO 14644-1, measuring particles ≥0.5 µm and ≥5 µm both at rest and in operation (including simulated operations). These are the maximum total particle concentration limits per m³ from Table 1 of Annex 1 2022:
| 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 |
Two practical notes: for Grades A and B, classification at ≥5 µm is no longer required but may be considered where indicated by the CCS or historical trends; for Grade D in operation, limits are not predetermined and must be set by the manufacturer based on a documented risk assessment.
Equivalences with ISO 14644-1 classes
On ≥0.5 µm counts, the practical correspondences are: Grade A equivalent to ISO 5 (at rest and in operation), Grade B ISO 5 at rest and ISO 7 in operation, Grade C ISO 7 at rest and ISO 8 in operation, Grade D ISO 8 at rest. Be careful though: the equivalence only applies to particle classification. An ISO 5 certificate does not “promote” a room to Grade A, because a GMP grade also carries microbial limits, continuous monitoring, gowning requirements and airflow dynamics that ISO 14644-1 does not cover. Confusing the two systems is the root cause of many audit gaps.
Topics like this change with every regulatory revision: with The Pragmatic GMP, GuideGxP's free weekly newsletter, you get updates on Annex 1, cleanroom classification and contamination control every week, already translated into operational actions.
Microbial limits: the action levels of Table 6
Alongside physical classification, Annex 1 sets action levels for microbial contamination during qualification:
- Grade A: no growth – for all methods (air sample, settle plates, contact plates, glove print). Any recovery requires an investigation.
- Grade B: 10 CFU/m³ in the air sample; 5 CFU/4 hours on a settle plate (90 mm); 5 CFU per contact plate (55 mm); 5 CFU per glove (5 fingers).
- Grade C: 100 CFU/m³; 50 CFU/4 hours; 25 CFU per contact plate.
- Grade D: 200 CFU/m³; 100 CFU/4 hours; 50 CFU per contact plate.
The move of Grade A from “<1 CFU” to “no growth” is one of the most cited changes in post-2023 inspections: environmental monitoring SOPs still quoting the old limit are an easy finding.
Classification and monitoring: two different exercises
Classification (and periodic requalification) demonstrates that the room is capable of meeting its grade; routine environmental monitoring demonstrates that it actually does so during production. Annex 1 dedicates separate tables to the two exercises: in-operation monitoring of Grade A and at-rest monitoring of Grade B include, for example, a limit of 29 particles/m³ at ≥5 µm, intended as an early warning signal rather than a classification criterion. In Grade A, particle monitoring must also cover the full duration of critical processing. Mixing up the two tables – or using the wrong one in the monitoring system specifications – is a recurring mistake.
Operational requirements per grade: airflow, pressures and requalification
Beyond particle counts, each grade carries dynamic requirements. In the Grade A zone, unidirectional airflow must maintain a homogeneous air speed within the guidance range of 0.36–0.54 m/s at the working position, verified through airflow visualisation studies. A minimum pressure difference of 10 Pa (guidance value) should be maintained between adjacent rooms of different grades. Periodic requalification has a defined maximum frequency: every 6 months for Grades A and B, every 12 months for Grades C and D, and after significant changes to rooms or systems. Finally, each grade imposes its own gowning standard, up to full sterile gowning with hood, goggles and sterile gloves for operating in Grade A/B.
Typical audit findings
- Declaring a room “Grade A” based solely on an ISO 5 certificate, without microbial limits, continuous monitoring and airflow studies.
- SOPs and specifications still quoting Annex 1 2008 limits (e.g. “<1 CFU” in Grade A or 20 particles ≥5 µm).
- Requalification treated like initial classification, without respecting the 6/12-month maximum intervals.
- Grade D “in operation” limits missing or copied from other sites without a local risk assessment.
- No documented link between assigned grades and the CCS: the grade map exists, but it is not justified.
GuideGxP recommendation
Treat the grade map as a living CCS document: for each room, record the grade, the ISO equivalence used for classification, the applicable limits (classification, monitoring, microbiology), the date of the last requalification and the next due date. A simple register structured this way answers inspectors' most frequent question in minutes: “why is this operation performed in this grade?”.
If you are designing, qualifying or requalifying your classified areas, the GuideGxP Operational Guide to Cleanrooms and HVAC Systems in GMP supports the whole journey – from URS and zoning to ISO 14644 testing and requalification – with ready-to-use toolkits and checklists.
Official sources
- EudraLex Volume 4 – Annex 1: Manufacture of Sterile Medicinal Products (2022 revision, European Commission)
- EudraLex Volume 4 – EU Guidelines for Good Manufacturing Practice (European Commission)
- ISO 14644-1:2015 – Cleanrooms and associated controlled environments – Part 1: Classification of air cleanliness by particle concentration
- PIC/S – Guide to GMP PE 009, Annex 1 (PIC/S harmonised version)
