Cleanroom design and air quality

Cleanroom Design and Air Quality

Sterile and hazardous compounding must happen in a controlled environment that limits contamination from particles, microorganisms, and chemical hazards. USP <797> (sterile compounding) and USP <800> (hazardous drugs) set specific engineering and environmental standards. Understanding cleanroom layout and air quality is essential before you ever enter a compounding suite.

The ISO Classification System

The International Organization for Standardization (ISO) classifies cleanrooms by the number of airborne particles allowed per cubic meter at a defined particle size. The lower the ISO number, the cleaner the air.

• ISO 5 is the cleanest classification required in pharmacy compounding. It permits the fewest particles and is where the actual compounding work takes place inside the primary engineering control (PEC).
• ISO 7 describes the buffer room (also called the buffer area), the room surrounding the PEC where pharmacists and technicians work and store compounding supplies.
• ISO 8 describes the anteroom, the transitional space between the general pharmacy and the buffer room.

Think of these zones as a series of nested clean bubbles: the anteroom is cleaner than the general pharmacy, the buffer room is cleaner than the anteroom, and the PEC inside the buffer room is the cleanest point of all.

The Anteroom (ISO 8)

The anteroom serves as an airlock and gowning area. Personnel don personal protective equipment (PPE) here before entering the buffer room. Supplies are often decontaminated or unpacked in the anteroom to reduce particle and contamination loads brought in from outside. For hazardous drug compounding under USP <800>, the anteroom must maintain negative pressure relative to the general pharmacy to keep hazardous vapors from migrating outward.

The Buffer Room (ISO 7)

The buffer room houses the PEC and is where most sterile compounding activity occurs. For non-hazardous sterile compounding, the buffer room is maintained at positive pressure relative to the anteroom so that any air movement flows outward, pushing contaminants away from the clean space. For hazardous sterile compounding, the buffer room is maintained at negative pressure relative to the anteroom, containing any hazardous drug particles or vapors within the room.

USP <797> specifies minimum air changes per hour (ACPH) for buffer rooms to continuously dilute and remove airborne particles. Actual requirements depend on room classification and whether the space is cleanroom-grade or segregated; always follow current USP <797> and your facility's standard operating procedures for the specific number in your setting.

Primary Engineering Controls (ISO 5)

The PEC is the device or workstation that provides the ISO 5 environment where compounding actually occurs. Four main PEC types are used in pharmacy:

1. Laminar Airflow Workbench (LAFW) — Horizontal or vertical laminar flow workbench. HEPA-filtered air flows over the work surface toward the operator. Used for non-hazardous sterile compounding. Never use an LAFW for hazardous drugs because contaminated air blows toward the compounder.

2. Biological Safety Cabinet (BSC) — Draws air inward and exhausts through a HEPA filter, protecting both the product and the operator. Used for hazardous sterile compounding (e.g., chemotherapy).

3. Compounding Aseptic Isolator (CAI) — A closed, glove-box style unit for non-hazardous sterile compounding. Provides ISO 5 air inside an enclosed chamber without requiring a full ISO 7 buffer room in some configurations, subject to USP <797> conditions.

4. Compounding Aseptic Containment Isolator (CACI) — A closed, glove-box style unit for hazardous sterile compounding. Maintains negative pressure inside the isolator to contain hazardous drug vapors and particles.

HEPA Filtration

High-Efficiency Particulate Air (HEPA) filters remove at least 99.97% of airborne particles 0.3 micrometers in diameter or larger. Every PEC and every cleanroom HVAC system uses HEPA filtration to maintain ISO standards. Filters must be certified and tested at installation and on a regular schedule thereafter. A damaged or improperly seated HEPA filter immediately compromises the entire ISO classification of that area.

Air Pressure Relationships

Pressure differentials between zones are critical safety controls. The general rule is:

• Positive pressure rooms push air out — used for non-hazardous sterile compounding buffer rooms to keep contaminants out.
• Negative pressure rooms pull air in and exhaust through filters — used for hazardous drug areas to contain dangerous particles and vapors.

Pressure gauges (magnehelic gauges or electronic monitors) are installed between zones. Staff must check and document pressure readings at the start of each shift. If pressure falls outside the acceptable range, compounding must stop and the issue must be reported and corrected before work resumes. This is a direct patient and worker safety requirement.

Safety Points

• Never bring items from the general pharmacy directly into the buffer room without decontamination in the anteroom.
• Always verify pressure readings before beginning any compounding session.
• Never use an LAFW for hazardous drugs — it puts you and others at risk.
• Report any HEPA filter damage, unusual particle counts, or pressure deviations immediately.
• Proper gowning before entering the buffer room is not optional; skin and hair shed particles that contaminate the ISO 7 environment.
• USP <800> requires additional containment measures (such as closed-system transfer devices) even inside the correct PEC when working with hazardous drugs.