Beating the Surge with Control of Airborne Exposure

PRACTICAL TOOLS TO PREVENT AIRBORNE VIRUS TRANSMISSION RISK

�KAREN COHN, MS, CIH | @COHNKAREN | #COVIDISAIRBORNE | JANUARY 2021

https://youtu.be/8sz604vriAM

Learning Objectives:

1. Explain in your own words how the virus is airborne and how to control it
2. Be able to inform and clarify public health messaging from others

​

​

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

Control strategies are additive - considered as layers of protection

Shelly L. Miller, University of Colorado Boulder, Aerosol Society Superspreading and how to minimize transmission.pdf

No single public health strategy can control all viral transmission

�

​

​

Multiple layered interventions cumulatively add protection

​

Full article and diagram, https://www.bmj.com/content/370/bmj.m3223

​

AIRBORNE TRANSMISSION

SCIENTIFIC PROOF HAS BEEN ESTABLISHED

​

​

https://its-airborne.org/covid19-timeline.html#event-fact-the-principal-mechanism-of-covid-19-infection-is-aerosol

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

​

​

https://science.sciencemag.org/content/sci/368/6498/1422.full.pdf

​

​

​

​

Imaging technique shows masks restrict exhaled air

“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

​

Note how the mask reduces emissions, causing smaller, slower exhalations which gradually rise up, also reducing risk to others

Ensure the mask fits well, or

it won’t do its job effectively!

https://www.fixthemask.com/

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 during breathing and speaking�-OR-
• Role play telling a family member who balks at wearing a mask about short-range airborne exposure

​

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 travel and 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

Scientists in the US have shown in the laboratory that the virus can survive in an aerosol and remain infectious for at least three hours

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�
• This is an illustration of long-range aerosol exposure, meaning at room-scale. In this setting, people can become infected without being in close contact with the infected person

​

​

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)

Let’s say the room lacks adequate air circulation and they stay for 1 hour, breathing normally.

100 people breathing for 60 mins. = 100 x 600L = 60,000 liters of air total per hour

Small group breakout exercise #2

• Role play a contact tracer’s request to a newly-identified contact to begin quarantine, explaining to them the risk at parties, bars and restaurants from shared air, at both short and long-range -OR-
• Role play telling your friends why you won’t dine out indoors and why you think 60-90 minutes at the table is unsafe

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 Twitter #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

http://cires1.colorado.edu/jimenez/COVID/2020_10_28_COVID_Aerosols_Jimenez_UnivZaragoza.pdf

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 http://cires1.colorado.edu/jimenez/COVID/2020_10_28_COVID_Aerosols_Jimenez_UnivZaragoza.pdf

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

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. �

1. Measured carbon dioxide goes down when windows are opened.�
2. Improving ventilation and/or filtration are as important as wearing as mask, because we need to protect at both room-scale and close contact.

​

​

​

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/

Small group breakout exercise #3

• Role play a health educator speaking to a school principal on ways they could control airborne transmission in their school, explaining the use of occupancy and duration limits, carbon dioxide monitoring, and opening windows.�-OR-
• Have this same conversation with your office manager at work.

CONTROLLING ROOM AIR CONDITIONS

STRATEGIES TO BRING IN OUTSIDE AIR, FILTER AND HUMIDIFY ROOM AIR

MODULE 2

What are ventilation & filtration?

Ventilation means adding outside air. Adding outdoor air dilutes the concentration of virus-laden particles in indoor spaces. There are two ways to improve ventilation:

1. Ventilation can be achieved mechanically, if there is an HVAC system
2. 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

1. These filters are specifically designed to entrap microscopic viruses
2. Typically, homes & 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.
• A single fan, as shown here, can be used to either “push” inside air outside or “pull” fresh air inside.
• Anytime of year, we can push air through the room by creating a cross-ventilation wind tunnel: 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.

https://covidstraighttalk.org/indoorwindtunnel

​

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

Small group breakout exercise #4

• 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

See http://healthyheating.com/

for emergency isolation room guidance

​

-Shared by Robert Bean,

ASHRAE Distinguished Lecturer, motto: Design for People, Good Buildings Fellow, retired member of APEGA & ASET. Life Member RPA, @healthyheating

See http://healthyheating.com/ for emergency isolation room guidance

Small group breakout exercise #5

• 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

An 8-year-old girl watched a video of @kprather88 explaining airborne transmission on CBS News with @DrLaPook

Along with this drawing, 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?"

Later, she wrote this poem:�

In The Air

COVID can be anywhere

Spreading in the air we share

Breathing, talking, singing, shouting

Sends the virus on an outing

Outside it will fly away

Inside it will stay all day

Clean the air and wear a mask

Stop the virus, that’s our task!

​

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 ESTIMATOR�

RESOURCES ON TRANSMISSION & PREVENTION OF COVID-19

Worker protection standards

https://covidstraighttalk.org/

​

https://www.dir.ca.gov/dosh/coronavirus/general-industry.html

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? “

https://tinyurl.com/FAQ-aerosols

​

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“

https://tinyurl.com/FAQ-aerosols

​

“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.”

​

Resources on transmission & prevention of COVID-19

https://bit.ly/3fzmB16