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Ventilation open window wearing mask covid safety

SARS-CoV-2, the virus that causes Covid-19, can float in the air like smoke. Aerosolized particles can linger in poorly ventilated indoor spaces, spreading farther than 6 feet from its source. We need to think about controlling the source of the virus indoors, about ventilation (mixing more outdoor air with indoor air), and about air filtration and cleaning devices.

Bring in as much outside air as you can thru the HVAC system. Avoid re-circulating air. Important to measure CO2 levels when people are present. Levels need to be <800 ppm. ARANET4 is a great sensor that can be used to assess. If you can’t ventilate through HVAC, open windows and doors for a cross breeze.

New research also shows the importance of keeping CO2 levels low because high CO2 concentration can actually create an environment that keeps airborne virus particles infectious for a longer amount of time. So it isn’t only about dilution of particles, but also about the chemistry of the air contributing to either decay of the virus (low CO2) or prolonging infectivity in a space (poor ventilation, high CO2)

This video is a great 5 minute explainer:

How Carbon Dioxide Increases a Virus’s Lifetime in the Air – Al Haddrell

The study: Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk
source: (visit for more languages)


The White House Office of Science and Technology Policy: Let’s Clear The Air On COVID

“The most common way COVID-19 is transmitted from one person to another is through tiny airborne particles of the virus hanging in indoor air for minutes or hours after an infected person has been there. While there are various strategies for avoiding breathing that air – from remote work to masking – we can and should talk more about how to make indoor environments safer by filtering or cleaning air.”

“Ventilation: Bringing in clean outdoor air is key. Indoor air moves less than outdoor air, so virus particles hang in the air in greater concentrations. Ventilation strategies that bring in more outdoor air can disperse viral particles and lower the risk of people inhaling them or getting infected through their eyes, nose, or mouth. Fans and HVAC systems can help make open windows more effective by pulling in clean outdoor air, and can send clean air into rooms without windows or good ventilation. New buildings are often constructed to seal air in for energy efficiency, so their HVAC systems must be on or their windows opened to clear the air. Older buildings may be less well sealed, but have outdated air handling systems or lack them altogether. An HVAC expert can help with this; more resources are available here.”

EPA: Clean Air in Buildings Challenge
Guidance to Help Building Owners and Operators Improve Indoor Air Quality and Protect Public Health

CDC: Ventilation in Buildings

CDC website now emphasizes coronavirus spreads in the air

Coronavirus is in the air. Here’s how to get it out.

How to stop student COVID spread as school year kicks into gear

The Plan to Stop Every Respiratory Virus at Once

Vehicle ventilation

Covid study: How to avoid catching virus in a shared car

“For driving below 30mph (48kph), opening all four windows is most beneficial.
But on faster roads, opening two on a diagonal can have an even bigger impact.”

more to come…