Detailed Interpretation of Cleanroom Grades A/B/C/D

Detailed Interpretation of Cleanroom Grades A/B/C/D

When it comes to the production of sterile pharmaceuticals, cleanroom classification is fundamental knowledge. However, do you truly understand the characteristics and applicable scenarios of Grades A, B, C and D? Article 14 of the new regulation provides clear definitions, yet definitions are static while practical applications are dynamic. Today we will thoroughly discuss this topic.

I. Official Definitions

Original text of Article 14 of the new regulation:

“The cleanrooms required for sterile pharmaceutical production are divided into four grades as follows:

Grade A: Critical areas for high-contamination-risk operations, where unidirectional airflow shall be maintained.

Grade B: For high-contamination-risk operations, Grade B serves as the background environment for Grade A cleanrooms (excluding isolators). The differential pressure of Grade B cleanrooms shall be continuously monitored.

Grades C and D: Cleanrooms for operational steps with relatively low contamination risks in sterile pharmaceutical production.”

Concise memory formula: Grade A = Core Operation Zone, Grade B = Supporting Background Zone, Grades C & D = Peripheral Support Zones.

II. Grade A: Highest Grade, Absolute Critical Zones

The core keyword of Grade A is “unidirectional airflow”.

Concept: Supply air filtered by HEPA filters flows downwards in an even, parallel pattern to remove particles and microorganisms generated during operations. The airflow velocity is generally maintained at around 0.45 m/s to guarantee airflow remains undisturbed before reaching the working surface.

Typical application scenarios for Grade A:

• Aseptic filling areas

• Internal working zones of open isolators

• Operating areas of open RABS

• High-risk operation points such as stopper washing and hopper feeding

A confusing distinction exists between Grade A inside isolators and Grade A inside RABS/open cleanrooms, specified in Articles 25 to 27 of the new regulation:

• The background environment of open isolators shall be at minimum Grade C

• The background environment of closed isolators shall be at minimum Grade D

• The background environment of RABS shall be at minimum Grade B

Therefore, it is insufficient to simply refer to “my Grade A area”; the background grade must also be specified.

III. Grade B: The Protective Barrier for Grade A

The definition of Grade B: “For high-contamination-risk operations, Grade B serves as the background environment for Grade A cleanrooms (excluding isolators).”

Key points of this clause:

1. Excluding isolators – isolators can adopt Grade C or D as background without requiring Grade B.
2. Background zone – the primary function of Grade B is to protect Grade A from contamination, so differential pressure must be continuously monitored to ensure air flows outwards from Grade B and prevents reverse flow.
3. High-contamination-risk operations – Grade B background is only required for high-risk operations using RABS or open cleanrooms, not all production activities.

Personnel gowning requirements for Grade B are the most stringent: sterile coveralls, double gloves, goggles, etc., are mandatory. Separate changing rooms shall be designated for personnel entering/exiting Grade B zones (Article 105 of the new regulation).

IV. Grades C and D: Low-Risk Zones That Cannot Be Neglected

Definition of Grades C and D: “Cleanrooms for operational steps with relatively low contamination risks.”

Note the wording “relatively low” rather than “zero risk”. Grades C and D remain integral parts of sterile production with merely controllable risks.

Typical applications:

• Grade C: Formulation areas for non-terminally sterilized products, peripheral environments of BFS equipment, late-stage changing rooms, etc.

• Grade D: Formulation areas for terminally sterilized products, material preparation areas, cleaning areas, etc.

There are obvious differences in environmental monitoring standards between Grade C and D. For airborne particles under dynamic conditions: Grade A requires virtually zero particles ≥5.0μm; Grade B limits particles ≥5.0μm to no more than 29 per cubic meter; standards for Grades C and D are far more lenient.

V. Common Confusion: Relationship Between Grades and Equipment

Many people ask: “Which grade should the sterilizer be placed in? Which grade for the RABS?” This question itself is incorrect.

The correct framing: “Which grade corresponds to a specific part of the sterilizer (e.g., the opening where vials are exposed)? What is the background grade of the RABS?”

Equipment does not equate to a fixed cleanroom grade. Different sections of a single piece of equipment may correspond to distinct grade requirements.

Article 137 of the new regulation provides detailed risk assessment guidance for isolator background environments, covering the following factors:

• Microbial decontamination procedures
• Automation level
• Impact of glove operations on first-pass air at critical process points
• Risks arising from compromised barriers or glove integrity
• Material transfer systems in use

VI. Airflow Design: Unidirectional vs. Non-Unidirectional Flow

Article 22 of the new regulation stipulates: Airflow pattern studies shall be performed for unidirectional airflow systems; such studies shall also be conducted for non-unidirectional airflow systems when necessary.

Grade A zones must adopt unidirectional airflow. Airflow pattern studies shall be visualized to verify the airflow design does not cause contamination retention or cross-contamination.

Grade B zones typically adopt turbulent or mixed airflow. Large-area Grade B zones would incur excessive energy consumption and costs with full unidirectional flow, yet turbulent airflow designs still require validation to confirm effective contaminant removal.

VII. Differential Pressure Control: Invisible Contamination Barriers

Article 23 of the new regulation: Differential pressure monitoring points shall be determined based on Contamination Control Strategy (CCS). Differential pressure indicators shall be installed at minimum between adjacent different-grade zones and between isolators and their background environments.

The essence of differential pressure lies in airflow direction. Grades A and B shall maintain positive pressure relative to external areas to ensure air flows outward only and block external contamination infiltration.

A widespread misconception: higher differential pressure equals better protection. Excessively high differential pressure causes difficult door operation, excessive stress on sealing components and increased energy consumption. A reasonable differential pressure range (typically 10–15 Pa) shall be determined via risk assessment of adjacent zones, with continuous monitoring implemented.

VIII. Practical Suggestions for Rational Grade Allocation

1. Avoid over-grading: Grade A is not mandatory for all operations. Isolator technology allows certain operations to be carried out under lower background grades, cutting costs while mitigating contamination risks.
2. Prioritize airflow organization: Cleanroom grades represent static standards, while airflow organization governs dynamic contamination control. Two Grade B zones with different airflow designs can deliver vastly different contamination control performance.
3. Align grades with process risks: Process risk assessment results shall determine which grade each operation is assigned to. Grades cannot be arbitrarily set before process planning.
4. Regular re-evaluation: When product formulas, production processes or facility equipment are modified, the original cleanroom grade layout shall be reassessed for rationality.