Directional Airflow

What, Where, & When?

J. Paul Jennette, MS, PE, RBPDirector of Biocontainment OperationsCornell College of Veterinary Medicine

The Purpose of Directional AirflowTo mitigate the risk of airborne contaminants being released from a high-containment laboratory, as a fundamental component of the laboratory’s (secondary) barrier function.

“mitigate”“secondary”

What is Directional Airflow?Directional Airflow is *not*the same as Differential Pressure

Airflow and DP

Q2

DP =(2610*A)2

DP = differential pressure (inches of water) Q = air flow (cfm) A = total leak area (square feet) 2610 = conversion factor

- ASHRAE Handbook of Fundamentals

Where Can We Have Directional Airflow?

• Within Rooms• Between Rooms• Across the Whole

Facility

WHO Biosafety Manual 3rd Ed., 2004

Where Can We Have Directional Airflow?

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corridor

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When Do We Need Directional Airflow?

(Note that “secondary barrier” implies the context for this question - that the lab is occupied, and that the directional airflow is not the first line of defense)

• Normal, steady state, conditions-?• Upset conditions-?

– External– Internal

External Upset: Airflow Reversal• Power failure &

transition to backup generator

• Exhaust Fan failure & transition to backup fan

External Upset: Airflow Reversal

Airflow Reversal Testing

Airflow Reversal – Before Tuning

Airflow Reversal – After Tuning

Internal Upset: Aerosol Release

• Equipment Failure

• Accident

• (Bad Behavior)

Aerosol Release Testing, 1

Aerosol Release Testing, 2

Aerosol Release Testing, 3

ante

corridor

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culture

Coincident Events for High Risk

• External Upset:

Airflow Reversal + Internal Upset

• Internal Upset:

Internal Upset + Open Door

Relative Probabilities

• External Upset:

(Airflow Reversal) (Internal Upset)

• Internal Upset:

(Internal Upset) (Open Door)`

Relative Probabilities

ResponseAt Cornell, we:1. Design and control containment HVAC systems

based on airflow offsets at critical doorways2. Verify containment performance by using smoke or

fog to test directional airflow at critical doorways3. Include multiple door transitions in designs4. Train containment lab users to open doors

efficiently5. Avoid lead/lag fan redundancy6. Tune our HVAC systems to minimize reversals