Controlling Airborne Virus with Ventilation and Masks

Beating the Surge
with Control of
Airborne Exposure
PRACTICAL TOOLS TO PREVENT AIRBORNE VIRUS
TRANSMISSION RISK
KAREN COHN, MS, CIH | @COHNKAREN | #COVIDISAIRBORNE | JANUARY 2021

Learning Objectives:
1. Explain how the virus is airborne and
how to control it as part of a case
investigation
2. Be able to inform and clarify public
health messaging

Why the surge in the U.S.?
►Seasonal, Economic and Behavioral Factors
►Absent or Confused Public Health Messaging

What’s been learned?
ALL people who have COVID-19 are contagious
to others up to two days prior to having symptoms
(that is while either asymptomatic or still pre-
symptomatic)
https://medical.mit.edu/covid-19-updates/2020/07/how-long-symptom-onset-person-contagious
and UCSF/UCLA COVID-19 Virtual Training Academy

Transmission is happening in homes &
social gatherings
https://www.governor.ny.gov/news/governor-cuomo-announces-updated-zone-metrics-hospital-directives-and-business-guidelines
► Transmission means
people becoming newly
infected after being
exposed to others who
are already infectious
► In New York State, three
months of case
investigation & contact
tracing interviews
revealed that 74% of
exposures were from
Household & Social
Gatherings

David Elfstrom @DavidElfstrom #WeAddAerosols
Public service announcement from Health Canada and
Public Health Agency of Canada originally showing
potential fomites, altered to show sharing exhaled
breath as a more urgent source of viral exposure
Note: Artistic plumes shown are for relatively still air...air flows created by HVAC systems, open windows, natural convection from
body heat or other surfaces will influence both the direction and speed of the exhaled plumes

…and at super-spreader events
► Many super-spreader events around the world
have been studied to look at transmission
pathways and possible controls, most notably the
Skagit Valley Chorale case
► In these events, a large number of bystanders
breathed the exhaled air of a highly contagious
person(s) in an indoor space, over an extended
time period (e.g. weddings, funerals, religious
services, call centers, restaurants, prisons)
https://www.cdc.gov/mmwr/volumes/69
/wr/mm6919e6.htm

Shelly L. Miller, University of Colorado Boulder, Aerosol Society Superspreading and how to minimize transmission.pdf
Control strategies are additive -
considered as layers of protection

No single public health strategy
can control all viral transmission
Multiple layered interventions cumulatively add protection
https://t.co/JqnTYDuTrR?amp=1

AIRBORNE TRANSMISSION
SCIENTIFIC PROOF HAS BEEN ESTABLISHED
MODULE 1

COVID is Airborne
“As long as we are
sharing an airspace
with someone else,
breathing in the air
that they exhale,
airborne transmission
is possible” -Virologist Julian
Tang, University of Leicester, UK

Maarten De Cock @mdc_martinus #WeAddAerosols
Unmasked officials at work with exhaled
breath visualized

What is airborne transmission?
► Airborne transmission occurs when we
inhale the air breathed out by an
infected person
► Exhaled breath contains particles
which are most concentrated in close
range to the person breathing or
speaking
► When everyone wears masks, keeps
socially distant and limits time spent in
shared airspace, we reduce breathing
in the exhaled breath of others

“The reach of exhaled air can be effectively reduced using a face mask as shown in
our video. A simple Schlieren imaging technique is applied to visualize the air flow
caused by a person breathing and coughing. Using a face mask the exhaled air flow
is blocked reducing effectively the risk of infection. Also nicely shown is the heat
transfer from the body to the cooler ambient air.”
More information about the Schlieren imaging technique is given here:
https://www.lavision.de/en/news/2020/4302/ https://www.lavision.de/cms_images/news/bos-
covid19.gif?m=1585647199
Imaging technique shows masks restrict exhaled air
Note how the
mask reduces
emissions,
causing smaller,
slower
exhalations
which gradually
rise up, also
reducing risk to
others

Maarten De Cock @mdc_martinus #WeAddAerosols | Singers exhaled breath visualized
Face shields can’t do the job of stopping exhaled breath!!!

David Elfstrom @DavidElfstrom #WeAddAerosols
Exhaled breath of political leaders visualized
“New York State Governor Andrew Cuomo to Protesters:
Wear a Mask, Not a Chin Guard” (June)
Jean-François Roberge, Minister of Education, Quéçbec (August)

Small group breakout exercise #1
►Role play a case investigator speaking
with a newly-identified case to request
their isolation from others, explaining
how virus-laden particles are exhaled
when they breathe or speak

INHALATION OF AEROSOLS
LEARN HOW AEROSOL EXPOSURE OCCURS AT NEAR AND FAR DISTANCE

Virus is carried by mucus-like particles -
Microscopic size particles predominate
1. Breath is exhaled as mucus-
like particles of varied size
and mass, both:
• Large visible particles
(droplets), and
• Microscopic particles
(aerosols)
2. Breathing, talking, coughing,
and other activities produce
~100-2000x more aerosols
than large droplets
Linsey C. Marr, https://www.nationalacademies.org/event/08-26-2020/docs/D24841CDA33D2FD785F6284AF128E7DE8EB1F56C7B4F

https://healthygibraltar.org/campaigns/
preventing-infection/transmission-of-
infection-droplets-and-aerosols/
Aerosols are light
enough to stay
afloat many hours,
accumulate and
stay infectious in
an enclosed
space

Smoke analogy to aerosols
Just like when a person blows out a puff of smoke, the particles are more
concentrated close up. Eventually these particles disperse throughout
the room. Even outdoors, you can smell someone’s exhaled smoke from
a distance. Viral particles travel and linger in air the same way.
http://cires1.colorado.edu/jimenez/COVID/2020_10_28_COVID_Aerosols_Jimenez_UnivZaragoza.pdf

Orla Hegarty @Orla_Hegarty #WeAddAerosols
Restaurant: Exhaled breath in shared air visualized

https://www.usatoday.com/in-depth/graphics/2020/07/16/why-bars-hotspots-covid-19-transmission/5389988002/ and
van Doremalen, N. et al. N. Engl. J. Med. http://doi.org/ggn88w (2020)
Shared air in a bar
► The blue shading shows exhaled
air in a bar that has no air
replacement from outdoors, when
occupied by 100 people
breathing normally for one hour
► Scientists in the United States have
shown in the laboratory that the
virus can survive in an aerosol and
remain infectious for at least three
hours

►Role play a contact tracer’s request
to a newly-identified contact to
begin quarantine, explaining to them
the risk from shared air at parties, bars
and restaurants

MEASURING CARBON DIOXIDE
CO2 MEASUREMENT INDICATES CONCENTRATION OF EXHALED BREATH

Elevated CO2 = Inadequate Ventilation
► Carbon dioxide (CO2) is generated when
we breathe. You can measure the room
concentration of carbon dioxide in units of
parts per million (ppm), using a simple meter
costing about $150. See #covidco2 for
examples of how to share your data with
friends and others.
► In well-ventilated spaces, CO2 should stay
below 700 ppm to reduce COVID-19
infection risk. Keeping the CO2 below that
level ensures that room air contains less than
1% of others’ exhaled breath.
https://tinyurl.com/FAQ-aerosols |
https://pubmed.ncbi.nlm.nih.gov/12950586/ |
https://theconversation.com/how-to-use-ventilation-and-air-filtration-to-
prevent-the-spread-of-coronavirus-indoors-143732

Ventilate to Reduce Elevated CO2
1. When the CO2 level is elevated, fresh
outdoor air must be added to dilute the
virus in room air (i.e. ventilation).
2. Preferably, change the mechanical
system (HVAC) to bring in more outside
air, which is then filtered and
temperature-adjusted. If no HVAC exists,
open the windows!
3. For schools and other shared indoor
spaces, the key is that the windows need
to be open all the time while people are
present at some level. This allows that
any continuously-exhaled virus is
constantly diluted and expelled
outdoors, and not allowed to
accumulate indoors.
https://tinyurl.com/FAQ-aerosols
https://theconversation.com/how-to-use-ventilation-and-air-
filtration-to-prevent-the-spread-of-coronavirus-indoors-143732
http://www.asahi.com/ajw/articles/13832094?s=09

https://threadreaderapp.com/thread/1334676863323660288.html
Elementary
school
classroom

See #covidco2 for more examples
Two adults
and one child
inside a
moving car

Even in non-pandemic times, properly ventilated buildings should have CO2 levels with a
floor or building average of 800 ppm or less (per International WELL Being Institute and
ASHRAE Standing Standard Project Committee 62.2)
Ventilation effectiveness | WELL Standard
https://www.ashrae.org/technical-resources/bookstore/standards-62-1-62-2
https://www.flandersinvestmentandtrade.com/invest/en/news/kraainem-flanders-issues-co2-meters-fight-covid-19

REDUCING AIRBORNE VIRUS INDOORS
TOOLS FOR AIRBORNE TRANSMISSION CONTROL

Dilute or entrap airborne virus to
reduce the risk of transmission
1. An infected person’s virus-laden exhaled
breath will become more concentrated in
room air unless it is diluted with fresh air or
entrapped on a high-efficiency filter.
2. Measured carbon dioxide goes down
when windows are opened.
3. Improving ventilation and/or filtration are
as important as wearing as mask.
CDC update of 12/8/20 on airborne spread and need for ventilation,
https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation.html

We can also make decisions that
reduce the risk of transmission
We can also limit the concentration of exhaled breath
in the room by:
1. Less people in the room (reduced capacity)
2. People in the room for shorter time periods,
allowing the room to be aired out in between
3. Limit occupancy and increase ventilation
wherever people take masks off to eat and drink
Richard L. Corsi, https://corsiairquality.wordpress.com/slides/

►Role play a health educator speaking
to a school principal on ways they
could control airborne transmission of
coronavirus in their school, explaining
the use of occupancy and duration
limits, carbon dioxide monitoring, and
opening windows

CONTROLLING ROOM AIR CONDITIONS
STRATEGIES TO BRING IN OUTSIDE AIR, FILTER AND HUMIDIFY ROOM AIR
MODULE 2

What are ventilation & filtration?
► Ventilation means adding outdoor air. Adding outside air dilutes the concentration
of virus-laden particles in indoor spaces. There are two ways to improve ventilation:
► Ventilation can be achieved mechanically, if there is an HVAC system
► The other is passive, which is letting outdoor air in through open windows and doors
► Filtration means a mechanism to entrap virus-laden particles onto high-efficiency
filters, such as a MERV-13 or HEPA filters
► These filters are specifically designed to entrap microscopic viruses
► Typically, homes and office buildings do not have this level of filtration
https://theconversation.com/keeping-indoor-air-clean-can-reduce-the-chance-of-spreading-coronavirus-149512

Mechanical ventilation strategies
Some buildings and homes have Heating, Ventilation & Air Conditioning
(HVAC) systems that bring in a portion of outside air to dilute the
recirculating air in the system. These are strategies to improve HVAC:
► Open the dampers to bring in a greater proportion of outside air
► Change the timers on HVAC systems to last a longer portion of each
day, such as before and after occupancy
► Upgrade HVAC filters to MERV 11 or greater so they can entrap
microscopic particle sizes
► Upgraded filters cause more resistance when pushing the air through,
so a HVAC professional should decide how much resistance the fan
motor can handle

Passive ventilation strategies
Without HVAC, fresh air can still enter a home
through open windows and doors and thus dilute
the exhaled breath in an indoor space (called
passive or natural ventilation).
► In the winter, heated air wants to escape
towards the colder air outside, which is another
reason that opening windows and doors can
dilute exhaled breath in an indoor space.
► Anytime of year, we can push air through the
room by creating cross-ventilation. This refers to
a fan placed to pull outdoor fresh air “in” at one
window, and another fan to push room air “out”
at a second window across the space.
► A single fan can also be used to either “push”
inside air outside or “pull” fresh air inside. Fans and exhaust vents can further increase ventilation
by pushing inside air outside. Makoto Hara/iStock/Getty
Images Plus via Getty Images

Ventilation by infiltration
https://www.colorado.edu/today/2020/10/28/ask-expert-staying-safe-winter-and-holiday-season-during-covid-19
Some homes have local exhaust fans in bathrooms and
over the stove in kitchens, which will remove indoor air.
Consider keeping those fans running continuously, for
example if you have visitors/workmen inside the home.
That exhaust (negative air pressure) will cause outside
air to infiltrate your home through uninsulated areas
and thereby increase your ventilation.
► For safety, you must ensure that windows are open
before creating this exhaust, so that carbon
monoxide from natural draft gas-burning
appliances and wood-burning fireplaces/stoves is
not drawn into the living quarters.
“In most homes, when you turn on the heat, you're
recirculating the indoor air through a coarse filter and it
can also increase the infiltration of air outside coming
in. So, in general, running your heat is going to be a
helpful thing to do to keep your indoor environment
clean.” -Dr. Shelley Miller, Professor Mechanical Engineering, CU Boulder

Temperature & humidity affect virus
Conditioning the air means changing the temperature of
room air. Germ-free humidifiers (with UV disinfection) safely
add moisture to room air. Relative humidity (RH) is the
measure of how much water vapor is in the air (relative to
how much it could hold at that temperature).
► Where climate and building envelope performance
permit, maintain 40-60% RH to reduce airborne
transmission. In colder climates, water may condense
from the air at that RH and lead to mold growth.
https://www.buildingscience.com/documents/reports/rr-0203-relative-humidity/view
► Cold, dry air keeps the virus alive. Keeping particles
moist prevents them from drying out and shrinking in
size. Smaller particles penetrate more deeply into the
lungs, causing more severe disease. Humidity also
improves the ability of our respiratory linings to counter
infections. https://www.dhs.gov/science-and-technology/sars-airborne-calculator

An air conditioner is not ventilation!
1. A window-mounted or room AC does not bring
outside air into the space, as that would create a
need to extract even more heat and humidity.
2. Using refrigerant, the AC extracts heat and moisture
from the room air, expels the extracted portion
outside, and blows the cooled and dehumidified
air back into the room. That air is 100% recirculated.
3. Furthermore, when the AC is on, it draws room air
through an air inlet grille with a very insufficient filter.
The filter removes larger airborne dust and particles,
which is not enough to prevent airborne infection.
4. If air conditioning is part of a building-wide HVAC
system, it’s possible to mix in outside air with the
recirculated air, but it’s not typically done because
of the energy costs which would be required to
reduce the temperature and humidity of the
outside air.

Known outbreaks caused by
air conditioner recirculated air
https://documentcloud.adobe.com/link/review?uri=urn:aaid:scds:US:630c042a-9c75-4950-9bad-9c40f6686fc0, Maarten De Cock

What’s a Portable Air Cleaner?
1. A Portable Air Cleaner is a stand-alone device
with a fan continuously drawing room air
through a high-efficiency filter (usually a HEPA
filter), and then adding the filtered air back into
the room
2. HEPA is acronym for "high efficiency particulate
air [filter]" which is designed to remove at least
99.97% of dust, pollen, mold, bacteria and any
airborne particles, from the microscopic size of
0.3 microns up to visible particles
3. AHAM Verifide portable air cleaners have been
tested and rated by the Association of Home
Appliance Manufacturers (AHAM) for their
ability to clean tobacco smoke, dust, and
pollen from a room, with a CADR (Clean Air
Delivery Rate) score for how well they remove
those pollutants from a room compared to
other models.
https://covidstraighttalk.org/air-cleaner-guide
Harvard-CU Boulder Portable Air Cleaner Calculator for Schools:
https://tinyurl.com/portableaircleanertool

Which Portable Air Cleaner is best?
1. Only purchase an air cleaner designed for the room size
where it will be used, to effectively clean the room air at the
rate described by the manufacturer.
2. The Clean Air Delivery Rating (CADR) measures how efficient
that equipment is at removing particulates over time. The
highest possible (i.e. most efficient) rating scores are 450 for
smoke and pollen, while 400 is the highest score for dust.
3. Choose an air cleaner with the highest CADR score for
smoke, due to its similarity in particle size with viral-loaded
aerosols.
4. Avoid air cleaner models with unnecessary add-on features
such as ozone generators, UV light beams or other
germicidal claims. CARB-certified air cleaners have been
tested and cannot emit more than 0.050 parts per million
(ppm) of ozone.
https://ww2.arb.ca.gov/our-work/programs/air-cleaners-ozone-products/air-cleaner-
information-consumers

Low Cost (DIY)
Portable Air Cleaner
1. Building scientists have designed their own
portable air cleaners using MERV-13 furnace
filters attached to portable box fans. They have
measured the effectiveness of these DIY devices
against wildfire smoke particles.
2. For the purpose of stopping microscopic
particles, the MERV-13 filter rating is almost the
same effectiveness as a HEPA filter. It can also
stop virus-laden particles.
3. Here is the best known DIY air cleaner, the “Corsi
Box Fan with 5 MERV 13 Filters”
https://www.texairfilters.com/a-variation-on-the-box-fan-with-merv-
13-filter-air-cleaner/
https://covidstraighttalk.org/boxfanairfilter

►Collectively as a small group,
summarize what you understand about
using ventilation and filtration to
protect day-to-day room occupants
from potential virus-laden exhaled
breath in the room’s shared air.

Ideal room interventions to keep an
infected person isolated
An infected person in an isolation room with these interventions can have good air
hygiene, with heated and humidified air. Ideally, the isolation room should be under
negative pressure relative to the rest of the home using this combination:
1. Sealing the room (including taping covers over any return air grills)
2. Using own bathroom, especially with an exhaust fan and/or operable window
3. Keeping the windows in room and bathroom open, along with running the
exhaust fan, to maintain a maximum 700 ppm CO2
4. Placing either a stand-alone commercial HEPA air cleaner or a DIY air
cleaner (MERV-13 filter/fan assembly) in the room
5. Adding a humidifier with UV-water treatment
6. Adding an electric space heater -Notes from Robert Bean, @healthyheating

►Collectively as a small group, recall
several isolation room interventions
which can keep an infected person’s
exhaled breath from infecting others
in the same living space

Sept. 29...8-year-old
daughter watched a
video of @kprather88
explaining airborne
transmission on CBS News
with @DrLaPook.
She said, "Wow...So when
we talk we make lots of
invisible spit-balls that
float in the air? And
that's how COVID gets
around? It floats around
in invisible spitball
spaceships?"

MORE RESOURCES
● WORKER PROTECTION STANDARDS
● FAQs ON PROTECTING YOURSELF FROM COVID-19 AEROSOL
TRANSMISSION
● ADDITIONAL CONTROL STRATEGIES RELATED TO GERMICIDAL UV &
FECAL TRANSMISSION
● AEROSOL TRANSMISSION RISK ESTIMATORS

https://covidstraighttalk.org/
https://www.dir.ca.gov/dosh/coronavirus/general-industry.html
Worker protection standards

Additional control strategies from the FAQs
Germicidal UV light
“Germicidal ultraviolet light (gUV,
also UVC) is an effective
technology to use to supplement
ventilation. It is especially useful for
increasing effective air change
rates in spaces that are heavily
occupied, and have the potential
for unsuspected infectious persons
inside...Dr. Shelly Miller has been
studying gUV for over 20 years and
here is a link to slides from a
presentation she gave in April 2020.
For a summary and additional
citations, see section 2.4 of the
following paper that was published
by some of the authors of this FAQ:
How can airborne transmission of
COVID-19 indoors be minimised? “
Fecal aerosols pathway
“Virus can potentially spread via
aerosols from toilets in two ways.
First, flushing a toilet can
generate aerosols: almost none
for gravity-fed toilets used at
home to millions for commercial
flushometer toilets found in many
public buildings in the US. The
total volume of aerosols
generated by a commercial
toilet is low, comparable to the
amount produced when a
person says “Hello, world!”...That
said, it’s still a good idea to close
the lid, if present, before flushing“
“Second, it is possible for fecal
aerosols to spread through
the plumbing system that
connects units in a high-rise
building, as occurred with the
original SARS in the Amoy
Gardens apartment buildings
in Hong Kong, and several
similar outbreaks in China and
Hong Kong for COVID-19. In
this case, the problem is
bathroom floor drains (not
common in the US) with dry
traps that allow air from the
vent stack, which might be
contaminated with fecal
aerosols from other units, to
flow into your bathroom.”

Controlling Airborne Virus with Ventilation and Masks

Controlling Airborne Virus with Ventilation and Masks

Recommended

Recommended

More Related Content

Similar to Controlling Airborne Virus with Ventilation and Masks

Similar to Controlling Airborne Virus with Ventilation and Masks (20)

More from Iklimlendirme Sogutma

More from Iklimlendirme Sogutma (20)

Recently uploaded

Recently uploaded (20)

Controlling Airborne Virus with Ventilation and Masks