covid 19 aerosols: how airflow affects transmission
TRANSCRIPT
Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
3FLOW Copyright © 2020 1
Copyright © 2020
Covid 19 Aerosols: How Airflow Affects Transmission
Session 1B - Ventilation Safety Performance
www.3flow.com
Thomas C. Smith
President / CEO
Copyright © 2020
Improve Safety, Minimize Waste and Achieve Better Outcomes in Critical Workplace Environments
Experts in Ventilation Where Safety Counts
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Universities
Government
PharmaceuticalChemical
Biotechnology Industry
3Flow - 25 years of working with clients committed to safe, efficient
and sustainable facilities
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Labs and critical workspaces are specially designed to
protect people working with airborne hazards
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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“Poor ventilation imperils the lives of people”
This fact is well-documented!
Is the ventilation okay?
How do you know?
Commercial HVAC Systems are not intended to protect
people from exposure to aerosolized pathogens
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Poll 2
How many air changes per hour
(ACH) are required for safety?
It Depends
No One Knows
2 ACH
3 ACH
7 ACH
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Infected People are Mobile Emission Sources
Healthy People are Potential Receptors
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How do we safely occupy indoor spaces?
What factors influence the risk?
How do we determine risk?
What can be done to mitigate risk?
Can we provide an assurance of safety?
Risk Spectrum
Negligible
Extreme
Low
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HVAC systems condition and move air through the building
°T
Above Ceiling
Below Ceiling
Communal Air Space
Exhaust/Return
Air Supply
Recirculated Airvs.
Fresh Air
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Infections occur primarily within the
communal air space (below the ceiling)
°T
Are you downwind?
Infectious DOSE = Concentration x Duration
Infected People can emit more than 40,000 particles every 15 minutes
Infectious Dose for Influenza approximately 1900 – 3000 viable particles.
Infectious Dose for Coronavirus is currently unknown.
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HVAC Systems can serve multiple spaces with
different functions and operating requirements
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VFD%
100
°T
Waiting Areas &Conference Rooms
Procedure Rooms Offices Labs
How much flow is required, where is it required and when?
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Numerous Factors Influence Risk of Covid-19 Transmission
Numerous Factors Influence Covid-19 Risk
Occupant Type and Density
Occupant Proximity and Duration
Airflow Quantity and Distribution
Available Exposure
Control Devices
Design and Operation of
HVAC Systems
Filtration, Recirculation
and Re-entrainment
Potential for Aerosol GenerationOccupant Activities
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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We are committed to safe, healthy and sustainable facilities.
But … is my office safe?
A101
Training
Center
RestroomA102
Office
C107
Lab
B101
Conference
Room
A103
Server
Room
B106
Mechanical
Room
D110
Warehouse
A105
Support
Space
D106
Break
Area
Restroom
Restroom
Restroom
A104
Break
Area
D109
Support
Space
B102
Office
B104
Office
B105
Office
B103
Office
C104
Office
C103
Office
C106
OfficeC105
OfficeD108
Office
D107
Office
D105
Office
D104
Office
D103
Office
D101
OfficeC102
Reception
C101
Office
D102
Employee
Entrance
&
Staging
Restroom
160 SF
105 SF
105 SF
105 SF
345 SF100 SF
450 SF
185 SF145 SF
125 SF
85 SF85 SF
100 SF 135 SF
35 SF
35 SF
35 SF
35 SF
130 SF
130 SF50 SF
70 SF100 SF
190 SF
345 SF700 SF
215 SF
445 SF
725 SF750 SF630 SF625 SF
Offices
Break Area
Conference Room
TrainingCenter
Lab and Support Spaces
Warehouses
Reception
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Drawing from on our experience in labs, we conducted a
Covid-19 Risk of Transmission Investigation
The Investigation included:
• Part 1 – Evaluate Risk and Demand for Ventilation
– Survey and Identify Spaces of Concern
– Document HVAC and Other Safety Measures
• Part 2 – Inspect and Measure HVAC Operation
– Air Handling and Return Air Units Operational
– Measure Flow and Calculate Air Change Rates
• Part 3 – Conduct Airflow Visualization Tests
– Generate visible smoke
– Observe airflow patterns note areas of accumulation and stagnation
• Part 4 – Conduct Aerosol Tracer Tests
– Generate air tracer to simulate contaminant release
– Measure concentration accumulation, dispersion and decay
– Determine Ventilation Effectiveness
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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A Risk Assessment was developed to identify spaces of
concern and help prioritize our efforts
Risk Band Description Attributes
0 Negligible
• Vacant Space
• ≤ 1 Occupant
• Very Limited Access
• Proper HVAC Operation
1 Low• ≤ 1 Known Occupant
• Limited to no Visitors
• Proper HVAC Operation
2 Moderate
• Known Occupants
• Limited Visitors w/Short Duration
• Adequate Spacing
• Proper HVAC Operation
3 High
• Known Occupants
• Limited Visitors w/ Extended Duration
• Mixed Social Space and Close Contact
• Ventilation Issues
4Extreme(Special)
• Known Occupants
• Numerous, Frequent Visitors w/Extended Duration
• Close Personal Contact
• Aerosol Generating Procedures
• Ventilation Issues
Spectrum of
Risk
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We evaluated space occupancy and where people congregate
A101
Training
Center
RestroomA102
Office
C107
Lab
B101
Conference
Room
A103
Server
Room
B106
Mechanical
Room
D110
Warehouse
A105
Support
Space
D106
Break
Area
Restroom
Restroom
Restroom
A104
Break
Area
D109
Support
Space
B102
Office
B104
Office
B105
Office
B103
Office
C104
Office
C103
Office
C106
OfficeC105
OfficeD108
Office
D107
Office
D105
Office
D104
Office
D103
Office
D101
OfficeC102
Reception
C101
Office
D102
Employee
Entrance
&
Staging
Restroom
Known Occupant - Long Duration (> 1 hr )
Transient – Long Duration (> 1 hr )
Transient – Moderate Duration (< 1 hr )
Transient – Short Duration (< 15 mins )
Multiple Known Occupants
Long Duration
Multiple Known Occupants
Short to Moderate Duration
Multiple Transient Occupants
Long Duration
Aerosol Generating Activities
Known Occupant – Short Duration (< 1 hr )
Multiple Transient Occupants
Short to Moderate Duration
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Risk Profiles helped identify areas that may require greater scrutiny
and possible application of special safety measures
A101
Training
Center
RestroomA102
Office
C107
Lab
B101
Conference
Room
A103
Server
Room
B106
Mechanical
RoomD110
Warehouse
A105
Support
Space
D106
Break
Area
Restroom
Restroom
Restroom
A104
Break
Area
D109
Support
Space
B102
Office
B104
Office
B105
Office
B103
Office
C104
Office
C103
Office
C106
OfficeC105
OfficeD108
Office
D107
Office
D105
Office
D104
Office
D103
Office
D101
Office
C102
Reception
C101
Office
D102
Employee
Entrance
&
Staging
Restroom
160 SF
105 SF
105 SF
105 SF
345 SF100 SF
450 SF
185 SF145 SF
125 SF
85 SF85 SF
100 SF 135 SF
35 SF
35 SF
35 SF
35 SF
130 SF
130 SF50 SF
70 SF100 SF
190 SF
345 SF700 SF
215 SF
445 SF
725 SF750 SF630 SF625 SF
0 Negligible
1 Low
2 Moderate
3 High
4 Extreme/Special
Risk Scale:
Training Center
ConferenceRoomReception
Office
Lab
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We documented the type and location of air supply and exhaust
device in each space
A101
Training
Center
RestroomA102
Office
C107
Lab
B101
Conference
Room
A103
Server
Room
B106
Mechanical
Room
D110
Warehouse
A105
Support
Space
D106
Break
Area
Restroom
Restroom
Restroom
A104
Break
Area
D109
Support
Space
B102
Office
B104
Office
B105
Office
B103
Office
C104
Office
C103
Office
C106
OfficeC105
OfficeD108
Office
D107
Office
D105
Office
D104
Office
D103
Office
D101
OfficeC102
Reception
C101
Office
D102
Employee
Entrance
&
Staging
Restroom
Exhaust Hood
Lab Supply Diffuser
Exhaust Device
Return Air Grille
Air Supply Diffuser
Trane
3 Ton
Carrier
5 Ton
Rudd
3 Ton
Trane
4 Ton
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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We documented the type and configuration of HVAC systems
to focus on the Areas of Concern First
TrainingCenterRCB-3
Trane
4 Ton
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Investigation Part 2 – We Inspected and Measured HVAC Operation
AHU- ASupply – 1276 cfmExhaust – 1117 cfmOutside Air – 159 cfmFilter: MERV 8
131 cfm
Air Change Rate4.6 ACH
151 cfm156 cfm
98 cfm
540 cfm
76 cfm
45 cfm
62 cfm
142 cfm
188 cfm
101 cfm
101 cfm
42 cfm
247 cfm
134 cfm
137 cfm
137cfm107 cfm
540 cfm
AHU-A
Training Center Size = 700 ft2
Supply – 536 cfmExhaust – 540 cfmOutside Air – ? CfmTemp – 69 dFRH - 46%
Module A
Air Supply Flow
Thermostat Return Flow
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Investigation Part 3 – Airflow Visualization Tests
*** WARNING ***
The following may be disturbing to some Viewers.
Viewer Discretion is Advised!
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Investigation Part 3 – Airflow Visualization Tests
If you can keep your head when all about you are losing theirs ….RKWe generated smoke from the mouth of each mannequin
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Investigation Part 3 – Airflow Visualization Tests
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Investigation Part 3 – Airflow Visualization Tests
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Investigation Part 3 – Airflow Visualization Tests
Can you say Super Spreader?
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Investigation Part 3 – Airflow Visualization Tests
Yikes!
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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S3
S1 S4
S2
G
S5
S3
S1 S4
S2
S5
G
S3
S1 S4
S2
S5G
Investigation Part 4 – Quantitative Air Tracer Tests
VEFF Test - Aerosol Emission Challenge• Generation Rate: 2 to 4 lpm
• Record Concentration and Particulate Data (60 minute Cycles)
Test 4- Cycle 1 Test 4 - Cycle 2 Test 4 - Cycle 3
Generation Locations
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Investigation Part 4 – Quantitative Air Tracer Tests
Air Tracer Generator
Array of Particle Counters and Photoionization Detectors (PIDs)
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Covid 19 Aerosols: Investigation & Utilization of Ventilation to Improve Safety Indoors
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Concentrations accumulate during generation and reduce
when generation stops. Dose is the total exposure.
Accumulation Dilution / Removal
DOSE
Generation Stops(i.e. Infected Person Leaves)
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Investigation Part 4 – Quantitative Air Tracer Tests
VEFF Test – Generation at Mannequin A
S3
S1 S4
S2
S5
G
Concentrations throughout the space increased by 20%
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Investigation Part 4 – Quantitative Air Tracer Tests
VEFF Test – Generation at Center of Room
S3
S1 S4
S2
G
S5
Avg. Dose
S1-S5
Theoretical
Dose
4.45 1.28
VEFF Test – With Filters
Building 3Flow Room Training Center ACH 4.6
3.5VEFF Factor
0
5
10
15
20
25
30
35
40
0 500 1000 1500 2000 2500 3000
Co
nce
ntr
atio
n -
pp
m
Time - seconds
VEFF Test - Room Ventilation Effectiveness S1-S5 Aggregate Concentration and Theoretical Concentration
S1-S5 Agg Theoretical
Ventilation Effectiveness is 3.5 times worse than Theoretical Well-Mixed Case
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Topics for Session 2
• Conducting a proper site investigation
• Methods to identify spaces of concern
• Evaluating Airflow Patterns and Air Change Rates
• Evaluation of Ventilation Effectiveness
• Diagnostics and Troubleshooting
• Methods and Measures to Improve Performance
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Submit Your Questions
Thank You!
Thomas C. Smith919-319-4290
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