Which ISO Class is common to both buffer room and anteroom?

• A. Class 7
• B. Class 5
• C. Class 3
• D. Class 9

Answer: (A)

The concept here is how air cleanliness is structured in a sterile environment. ISO classifications measure how clean the air is, with lower numbers meaning fewer particles. In sterile compounding, the most critical work happens in the ISO 5 zone inside the primary engineering control (the hood or isolator). The spaces surrounding that zone—the buffer room and the anteroom—are transitional areas that must maintain a consistent level of cleanliness to protect the ISO 5 zone.

Having both the buffer room and the anteroom at the same ISO Class (Class 7) provides a stable barrier as personnel move in and out. The anteroom acts as an airlock for donning, doffing, and reducing entrainment, while the buffer room serves as the last before entering the ISO 5 area and supports the workflow. Keeping these spaces at Class 7 helps prevent contaminants from moving from outside into the clean environment and ensures the integrity of the sterile work area.

Other ISO levels would either be too stringent for routine transitions or not clean enough to protect the ISO 5 zone, which is why Class 7 is the common designation for both spaces.