How do I protect myself?

Ventilation

Knowing the CO₂ level is one thing. But then you need to do something about it.

First, let outside air in, wherever possible. Open windows, doors and get a draught flowing through. A standalone fan really helps.

You can see the dramatic effect on air quality which that simple intervention had in a pharmacy. And here you can see just how quickly switching OFF recirculate in a car improves the CO₂ level: In the car.

The Germans, who have always been keen on fresh air, have been stressing ventilation (or “Lüften”) for months. Click on the image from the Guardian for more info:

Filtering

But what if opening the window isn’t enough?

If you can’t get the CO₂ level down sufficiently by increasing ventilation then you can filter the air to remove dangerous particles, such as coronaviruses, and also dust and allergens.

There are many air filters on the market. They can be quite expensive, but it is easy to build an effective one yourself very cheaply.

Here are some terrific resources on the subject:

Wired: Could a Janky, Jury-Rigged Air Purifier Help Fight Covid-19?
Medium: Air Purifiers, Air Filters, and the Best DIY Hacks to Reduce the Coronavirus Risk
How to improve the air quality in your home (Includes short video with Dr Richard Corsi)

Remember that if you are filtering the air, the CO₂ level will become an unreliable indicator of how contaminated it is. This is because the filter removes the particles, but not the CO₂.

Even if you are filtering, though, it’s a good idea to try and get the CO₂ level down as much as you can, because a high CO₂ affects your cognitive function and makes you sleepy.

If your building has an integrated ventilation system, then talk to your ventilation engineer about improving the air quality.
​

More resources and national guidance

This Google doc has been created by the world's leading aerosol scientists and is regularly updated and maintained. It is the leading source of information on the Internet:

For a superb presentation on how to reduce airborne exposure risk, Karen Cohn MS CIH, an industrial hygienist from California has produced a terrific presentation. You can view the slides here.

Or this is the full narration by Karen, lasting 32 minutes. Watch it. It is excellent:

A number of governments have produced excellent guidance on ventilation during the pandemic. (Not Australia, unfortunately!)

Canada: COVID-19: Guidance on indoor ventilation during the pandemic
USA (CDC): Ventilation in Buildings
USA (OSHA): COVID-19 Guidance on Ventilation in the Workplace
European Union: Heating, ventilation and air-conditioning systems in the context of COVID-19: first update
UK: Ventilation and air conditioning during the coronavirus (COVID-19) pandemic
USA (ASHRAE): ASHRAE Position Document on Infectious Aerosols
USA (AIHA): Joint Consensus Statement on Addressing the Aerosol Transmission of SARS CoV-2 and Recommendations for Preventing Occupational Exposures

Here are two calculators to estimate the risk of covid transmission. The first can be viewed here and is by Professor JL Jimenez at the University of Colorado.

The second calculator gives you some idea of what the individual risk of infection is with different room parameters and ventilation conditions. They are both interesting to play around with, as long as you don't take them too literally, but are probably beyond the scope of the casual user. Click on the image to open it in a new window:

Follow these Twitter accounts to keep up to date with developments on aerosol transmission and ventilation:

Want to learn more? Follow the experts. @kprather88 @jljcolorado @HuffmanLabDU @ShellyMBoulder @BarryHunt008 @j_g_allen @JimRosenthal4 @akm5376 @PrasadKasibhat1 @healthyheating @DavidElfstrom

— EndCoronaVirus.org (@endCOVID19) February 3, 2021

A clearly written Twitter thread explaining technical aspects of the Clean Air Delivery Rate by Dr Richard Corsi and how to calculate required ventilation rates for a typical classroom:

1/ Clean Air Delivery Rate (CADR). The CADR of a portable filtration system is:

CADR = f x Q.

f is the fractional removal efficiency of particles that pass through a device (value = 0 to 1). Q is the volumetric flow rate of air through the device (e.g., m3/hr, ft3/min). ...

— Richard Corsi, PhD, PE (Texas) (@CorsIAQ) February 6, 2021