What Should the CO2 Level Be In a Classroom?

The CO2 level in the classroom should be close to the outdoor CO2 level, which is about 413 ppm. However, achieving this means leaving all doors and windows open for air exchange, which is not always practical.

Indoor CO2 levels below 1100ppm are considered acceptable.

What Is the CO2 Level In the Outdoors?

You may have heard that the outdoor CO2 level has slowly been creeping up due to global warming. In 2021, the amount of carbon dioxide in the atmosphere was about 413 ppm. In other words, the air surrounding us is roughly 0.0413% CO2.

How Does CO2 Build Up In the Classroom?

As students exhale, carbon dioxide accumulates in the classroom. With time, the CO2 level starts to increase beyond the nominal 413 ppm.

The amount of carbon dioxide indoors can be well over 1000 ppm and can even approach 3000 ppm. The absolute CO2 level reached depends on the classroom's ventilation, fresh air intake, number of students, and volume.

A high CO2 concentration is generally unsafe as it has debilitating effects on students. See the video below.

How Does CO2 Relate to Airborne Virus Infection?

Along with exhaling CO2, students spray out micro droplets when talking, singing, or breathing. For sick students, these dispersed particles may contain pathogens that can remain suspended in the air for hours. 

As we exhale more and more, CO2 levels and airborne virus concentrations begin to rise within our surrounding environment.

How Can CO2 Be Reduced In the Classroom?

The CO2 levels can be reduced by controlling three key variables:

• Ventilation. The ventilation system controls the air change rate, or how much fresh air is getting into the classroom.
• Classroom volume. The larger the classroom, the longer it will take for CO2 levels to increase due to dilution effects.
• Student count. More students in the classroom leads to more carbon dioxide being exhaled and greater CO2 levels.

In the post-pandemic world, it is common to see schools upgrade ventilation systems, control student count, and hold classes in larger spaces.

What About Air Sterilization to Kill Airborne Pathogens?

Yes, air sterilization is a legitimate approach to disinfect airborne pathogens in the classroom. 

One commonly used approach is ultraviolet light, which zaps the virus and kills it in the air. The YouTube clip below explains more.

Has the Link Between CO2 Levels and Virus Infection Risk Been Scientifically Proven?

Yes it has. This relationship has been shown by research from the University of Colorado, Harvard School of Public Health, and MIT researchers.

The Technical University of Berlin showed that increasing uncontaminated air reduces indoor concentrations of CO2 and other aerosols. In turn, this strategy of fresh air ventilation lowers one's infection risk.

After considerable research effort, academics have concluded that keeping CO2 levels as low as possible will help reduce infection risk. Aerosol monitoring is an important first step, as seen by many school districts across the world adopting CO2 monitoring in the classroom.

How Do You Measure CO2 Levels In a Classroom?

Carbon dioxide is measured through a carbon dioxide monitor. This device has a sensor cell and works by detecting CO2 molecules via infrared light.

The infrared light is absorbed by CO2 molecules, an effect similar to the greenhouse gas effect warming up the Earth. Due to the light absorption from the CO2 molecules, this change can be detected electrically. A photodetector detects the decrease in infrared light received and the output signal is proportional to the CO2 gas concentration. 

Do Classrooms Require CO2 Monitors?

Monitor requirements depend on your state, city, and county. For example, Californian classrooms are now required to have a carbon dioxide monitor to track proper ventilation. This also ensures minimum risk in virus distribution, inhalation, and contraction.

In 2021, the California legislature passed AB841AB-841, requiring all classrooms to monitor CO2 levels.

What Are the Requirements for CO2 Monitors In Californian Classrooms?

• AB841 mandates that CO2 monitors must be mounted to the wall between three and six feet above the floor and at least five feet away from the door and operable windows.

• The monitor must display the carbon dioxide readings to the teacher through a display on the device.

• The monitor must provide a notification through a visual indicator or other alert system when the carbon dioxide levels in the classroom exceed 1100 ppm.

• The monitor must maintain a record of previous data, including the maximum carbon dioxide concentration measured.

• The monitor must have a range between 400 ppm and 2000 ppm.

• The monitor must be certified by the manufacturer to be accurate within 75 ppm at 1,000 ppm of carbon dioxide. The device must also function properly with calibration every five years or more.

What Is the Recommended Indoor CO2 Level?

We have collected a few interesting recommended indoor CO2 levels. These include the following:

• The California State legislature passed AB841 that requires classrooms to monitor CO2 and alarm at 1100 ppm.
• Washington State requires CO2 monitoring in restaurants and for the monitor to alarm at 450 ppm.
• The American Society of Heating, Refrigerating, and Air-Conditioning Engineers recommends indoor CO2 concentrations be maintained below 1000 ppm in schools and 800 ppm in offices.
• The Federal Environment Agency of Germany recommends classrooms and offices to not exceed 1,000 ppm.
• In Ireland, CO2 monitors are being installed in classrooms with poor ventilation.
• Germany’s Federal Environment Agency’s general guidelines for carbon dioxide in indoor air classifies any CO2 concentration between 1,000 and 2,000 ppm as questionable; anything above 2,000 is unacceptable.

Which Is the Best CO2 Monitor for Classrooms?

A monitor should ideally meet the AB841 requirements to be used within a classroom. There are some CO2 monitors that have been specifically designed for this purpose and are used in classrooms across California. See the video below for more information.

Final Words

Since the pandemic, school districts are improving indoor air quality through proper ventilation and CO2 monitoring. These actions are critical to keep our teachers and students safe in the classroom. 

You may like to ask your school district if any action has been taken to improve the air quality in the classroom. It is imperative to understand any new protocols, ventilation systems, or CO2 monitoring devices they have adopted or plan to implement.