The Dangers of High Carbon Dioxide (CO2) Levels

Although carbon dioxide (CO2) is a byproduct of many natural processes, high levels of CO2 can cause a variety of health effects on humans. This article explains at what levels CO2 becomes dangerous and the negative health effects of these high CO2 levels. Also, how do CO2 levels become high in the first place?

How Carbon Dioxide (CO2) Levels Become High

Carbon dioxide (CO2) gas is produced by both natural processes (respiration, volcanoes) and human activity (fossil fuels/deforestation). Indoor spaces are more at risk of high CO2 levels due to the lack of fresh air. Fresh air helps dilute high concentrations of CO2. 

Indoor spaces are at risk of high CO2 levels when large amounts of people occupy small spaces or have poor ventilation. This is because the CO2 produced through respiration by the occupants builds up over time and has nowhere to go.

Dangers of high CO2 levels
Humans are CO2 spewing machines

Even larger spaces such as grocery stores can have higher CO2 levels with enough occupants.

CO2 monitor in grocery story
Barrow’s original tweet thread on CO2 levels in public places

Homes can also be at risk when CO2 levels in the soil below are high and the gas seeps through the cracks in the basement floor and foundation. 

Carbon dioxide levels typically are not a concern outside but can reach dangerous levels during a volcanic eruption. Volcanoes emit large amounts of CO2 during eruptions.

The Danger of Carbon Dioxide to Humans

Unlike dangerous PM2.5 pollution, low levels of CO2 are not dangerous. But at higher levels, CO2 can displace oxygen resulting in a variety of negative effects on humans.

Typical outdoor carbon dioxide levels range from 350-450 ppm (parts per million). But carbon dioxide will build up if people are in an enclosed, unventilated room.

At moderate levels, CO2 makes people tired, affects cognitive skills, and causes headaches. Studies show even moderate increases in CO2 levels from 600 ppm to 1000ppm decrease cognitive ability and decision making.

At very high levels, CO2 can make people sick or even die.

How to Track CO2 Levels

To ensure CO2 levels do not reach dangerous levels in crowded areas, use a CO2 monitor. At Smart Air, our tests show simple CO2 monitors are very accurate.

How to Reduce CO2 Levels

To reduce CO2 levels in a room, ventilation needs to improve by introducing new fresh air into the room. This can be achieved by opening windows, and doors, or using central air and HVAC systems. Reducing the number of people in a room or finding a larger gathering space can also help lower CO2 levels.

Read More: Will Air Purifiers Work With Windows Open?

Bottom Line: When Do CO2 Levels Become Dangerous and What are the Health Effects?

Studies show even moderate increases in CO2 levels from 600 ppm to 1000ppm decrease cognitive ability and decision making. CO2 levels of 5000ppm can cause headaches, and levels of 70000ppm can kill you.

Smart Air


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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.