What are the core considerations for differential pressure gradient design in animal laboratories?

I. Core Design Principles

Irreversible Unidirectional Airflow: Airflow must flow from the clean area → feeding area → experimental area → waste area; reverse flow is strictly prohibited.

Pressure Differential Controlled Only by Supply and Exhaust Ventilation: Airflow must not rely on natural convection through door openings to prevent pressure differential reversal caused by personnel/animal entry and exit.

24-Hour Stability: Under dynamic disturbances (door opening and closing, personnel movement), pressure differential fluctuations should be ≤ ±5Pa.

Airtightness Priority: The enclosure structure (color steel plates, door seams, through-wall pipes, pass-through windows) must meet airtightness standards; otherwise, gradient failure will occur.

II. Standard Pressure Gradient Setting (SPF Barrier Environment)

Following the order: Clean Corridor > Feeding Room > Laboratory Operation Room > Waste Corridor:

Clean Corridor relative to outdoors: +10～+15Pa

Clean Corridor → Feeding Room: 5～10Pa

Feeding Room → Laboratory Operation Room: 5～10Pa

Laboratory Operation Room → Waste Corridor: 5～10Pa

Biosafety/Infected Animal Laboratory (Negative Pressure Core):

Gradient: Outer Buffer → Feeding/Experimental Area (Negative Pressure) → Waste Corridor (Even More Negative Pressure)

Core Area relative to outdoors: -20～-60Pa; Adjacent Areas ≥-25Pa

III. Supply and Exhaust Air Linkage Control Strategy

Start/Stop Logic: Exhaust air starts first, then supply air; shutdown is the reverse to prevent instantaneous positive pressure from spreading contamination.

System Selection:

VAV (Variable Air Volume) (Recommended): Dynamically adjusts airflow, adapts to door opening and closing, personnel disturbance, low energy consumption, and good stability.

CAV (Constant Air Volume): Simple structure but high energy consumption and poor disturbance resistance; only suitable for low-disturbance scenarios.

Interlocking and Alarm: Automatic alarm and interlock protection in case of fan failure or differential pressure exceeding the threshold (±5Pa) to prevent gradient reversal.

IV. Airlock/Buffer Room and Traffic Flow Design

Buffer Room Differential Pressure: The differential pressure between the two areas must not be equal to or lower than the contaminated side, forming a "pressure step" to block cross-flow.

One-Way Traffic Flow: Strict separation of personnel, materials, and animals; clean → contaminated flow in one direction to avoid cross-contamination.

Pass-through Window: Equipped with an airlock and disinfection function; both sides cannot be opened simultaneously to maintain gradient stability.

V. Enclosure Airtightness Assurance

Sealing Nodes: Strict sealing of color steel plate splicing, door seams (sealing strips), wall penetrations (sealing adhesive), and pass-through windows/doors (airtight structure).

Airtightness Test: With all passages closed, pressurize to 500Pa; pressure should decrease to <250Pa within 20 minutes to be considered合格 (qualified).

Leakage Control: Regular leak checks to prevent leakage from causing differential pressure establishment failure or frequent alarms.

VI. Regulations and Compliance Key Points

National Standards: GB 14925-2023 "Laboratory Animal Environment and Facilities", GB 50346 "Technical Specifications for Biosafety Laboratory Construction".

International Standards: ISO 14644 (Cleanroom), AAALAC certification requirements.

Acceptance: Static/dynamic differential pressure testing, airflow balance, air tightness testing; operation is only permitted after third-party verification.

VII. Common Problems and Mitigation

Pressure Reversal: Poor air tightness, malfunction of supply and exhaust air linkage, short circuit at air outlets (supply and return air outlets too close).

Large Fluctuations: Slow VAV response, poor door sealing, frequent personnel/animal entry and exit.

High Energy Consumption: CAV system, excessive differential pressure setting (>15Pa), exceeding air change rate limits.

In summary, the key to differential pressure gradient design is unidirectional airflow + stable layers + airtight enclosure + intelligent control. It strictly follows GB 14925 and biosafety standards, and sets the gradient according to the differences in SPF/infection risk to ensure reliable barriers, stable experiments, and controllable biosafety.