When a volunteer from the Naltic Industrials came to the White House Correspondents dinner with a CO2 sensor to measure the air quality, most of the general public had little to no understanding of the importance of air quality in indoor settings. 

Scientists who have been saying since the beginning of the pandemic that COVID is airborne got deeply concerned when they saw that the CO2 levels at the WHCA dinner were at 2063 parts per million (PPM). They were right.

Before we knew it, journalist after journalist, network executive after network executive got infected with COVID.

To make things even riskier, the President of the United States was in the room sitting on the same stage with those who got infected.

Why is CO2 important?

COVID is airborne. The virus particles exit the infected person’s mouth or nose, then float through the air like smoke, and you can get infected when you breathe enough of them in.

Ventilation is when indoor air is replaced with outdoor air, so when you have good ventilation, it removes those virus particles and replaces them with virus-free outdoor air.

When you are indoors, the amount of air you have exhaled will build up and the CO2 levels will start rising. Photo credit: SAF Tehnika JSC

Just like how COVID travels from one person to another, CO2 or carbon dioxide can too. CO2 is a gas that we are always breathing in and out. Unlike carbon monoxide, it isn’t deadly in small concentrations, but allows you to measure how much air is being rebreathed from other people instead of breathing clean air – it’s gaseous backwash.

Outdoor air CO2 levels are now around 420 parts per million (ppm) or 0.042%. This has slowly been climbing over the decades as we release more CO2 into the atmosphere by burning fossil fuels.

The CO2 levels in exhaled breath are much higher and are closer to 40000 ppm or 4%.

COVID is airborne.

When you are indoors, the amount of air you have exhaled will build up and the CO2 levels will start rising. Good ventilation can keep CO2 levels low. As a rough guideline, starting at 400 ppm, every additional 400 ppm is another 1% of rebreathed air, so 800 ppm means 1% rebreathed air, 1200 ppm is 2% rebreathed air and so on. 

That dinner had levels above 2000 ppm, so one out of every twenty-five breaths came from someone else’s lungs.

Why is ventilation important?

We have known from before COVID that students in schools with better ventilation had better test scores, lower absence rates, and fewer asthma and respiratory symptoms.

Other studies show that for every dollar an employer spends on improving ventilation, they make more than $160 in return through improved employee productivity and fewer sick days. This was all from before COVID and now it is even more important.

Mustafa shehadeh from Pixabay 

Quite often the ventilation equipment we rely on to provide fresh air stops working and no one notices. By monitoring CO2 levels with CO2 sensor, you will be able to see if it needs to get fixed right away.

What should the CO2 levels be?

There is no official cut-off between good and bad CO2 levels. ASHRAE, the organization that has been responsible for setting ventilation rates in buildings, has stated that CO2 levels below 1000 ppm has long been considered an indicator of good air quality.

The French High Council of Public Health recommends a threshold of 800 ppm in all public buildings. Levels above 800 ppm require action improving ventilation or reducing occupancy.

Photo credit: SAF Tehnika JSC

CO2 levels in properly ventilated spaces should stay below 1000 ppm. Unfortunately, many places with poor ventilation have CO2 levels between 1500 ppm to 2000 ppm.

Be careful when relying on CO2 as an indicator if a place is safe. It can be misleading if there are few people there. CO2 tells you the ventilation per person, but not the total amount of ventilation.

If you have a space with poor ventilation, but a window cracked open and low occupancy, then the CO2 levels might be low, even though the ventilation is poor. Sometimes low CO2 just indicates that there are not many people in the space instead of indicating good ventilation.

How to use CO2 sensor and ventilation to protect yourself from COVID?

If you care about protecting yourself from COVID, CO2 is one piece of the puzzle. Ventilation, filtration and UV all can work together to clean the air. Usually, ventilation is the most significant of the three and CO2 levels can tell you if it is working properly.

The easiest way to improve ventilation is to open windows and doors as much as possible. You can place fans in the windows or doors to further increase the airflow.

In most commercial spaces, the units that heat and cool the space also provide ventilation, so make sure the thermostat is set to “on” or “fan” and never leave it in “auto” when there are people there. You can put it in “auto” at night when everyone leaves.

Be careful when relying on CO2 sensor as an indicator if a place is safe. It can be misleading if there are few people there.

The furnace in your home is usually not connected to outdoor air unless you have a heat recovery ventilator (HRV) or energy recovery ventilator (ERV) connected to it, so running your furnace all the time will not help reduce the CO2 levels in your home.

If you put a MERV-13 filter in your furnace and run it all the time, it can still filter any virus particles from the air.

Photo credit: SAF Tehnika JSC

If you have a ventilation unit from the past 20 years in a commercial space, CO2 levels should be around 800 ppm (depending on the number of people).

Older units might leave you with levels around 1200 ppm. If the CO2 levels get too high, contact an HVAC professional to check if the ventilation is working. You could also ask them to increase the amount of outdoor air being brought in to lower the CO2 levels.

You could always add a stand-alone HEPA filter to clean the air, even though it won’t reduce the CO2 levels.

When you buy a CO2 sensor, make sure it has a non-dispersive infrared (NDIR) sensor. There are cheaper ones on the market, but they aren’t reliable.

CO2 sensor with CO2 levels should be displayed in all buildings. It sends a clear message that the person responsible for the space cares about the health and safety of everyone who enters.

Displaying CO2 levels isn’t about airing your dirty laundry. It’s laundering your dirty air.

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Joey Fox is a professional engineer, has worked in the HVAC industry for more than 10 years and is the chair of the Indoor Air Quality Advisory Group for the Ontario Society of Professional Engineers.

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