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Directional Airflow
What, Where, & When?
J. Paul Jennette, MS, PE, RBPDirector of Biocontainment OperationsCornell College of Veterinary Medicine
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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”
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What is Directional Airflow?Directional Airflow is *not*the same as Differential Pressure
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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
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Where Can We Have Directional Airflow?
• Within Rooms• Between Rooms• Across the Whole
Facility
WHO Biosafety Manual 3rd Ed., 2004
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Where Can We Have Directional Airflow?
ante
support
culture
corridor
culture
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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
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External Upset: Airflow Reversal• Power failure &
transition to backup generator
• Exhaust Fan failure & transition to backup fan
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External Upset: Airflow Reversal
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Airflow Reversal Testing
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Airflow Reversal – Before Tuning
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Airflow Reversal – After Tuning
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Internal Upset: Aerosol Release
• Equipment Failure
• Accident
• (Bad Behavior)
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Aerosol Release Testing, 1
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Aerosol Release Testing, 2
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Aerosol Release Testing, 3
ante
corridor
Xsupport
culture
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Coincident Events for High Risk
• External Upset:
Airflow Reversal + Internal Upset
• Internal Upset:
Internal Upset + Open Door
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Relative Probabilities
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• External Upset:
(Airflow Reversal) (Internal Upset)
• Internal Upset:
(Internal Upset) (Open Door)`
Relative Probabilities
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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