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Carbon Dioxide Levels Chart

dangerous co2 levels

Our carbon dioxide (CO2) levels chart shows the increasing danger of elevated levels of CO2 in enclosed spaces. 

Even a small increase of CO2 in the air by volume can be hazardous. While most people will never encounter CO2 levels above 1% indoors, the increased use of pressurized CO2 storage tanks in businesses has increased the likelihood of exposure to high levels of CO2. At 1% CO2, people can start to experience accelerated heart rate. At 4%, CO2 levels can be fatal.

What is an acceptable CO2 level in a room?

Normal CO2 levels in fresh air is approximately 400 ppm (part per million) or 0.04% CO2 in air by volume. The table below shows the effects of increased CO2 levels in an enclosed space as a percent of air by volume.



Normal outdoor air



Typical CO2 levels found indoors



 Common complaints of drowsiness or poor air quality



Headaches, fatigue, stagnant, stuffiness, poor concentration, loss of focus, increased heart rate, nausea

> 50,000ppm

> 5%

Toxicity due to oxygen deprivation occurs

> 100,000ppm

> 10%

Oxygen deprivation in seconds: convulsions, coma, and death


Click here to view a CO2 levels reference chart, you can print.

The acceptable level of carbon dioxide (CO2) indoors can vary depending on factors such as the purpose of the space, the number of occupants, and ventilation systems.

Generally, indoor CO2 levels are measured in parts per million (ppm). The following are some common guidelines:

  1. General indoor environments: In most indoor settings, a CO2 concentration of 400-1000 ppm is considered acceptable. This range is commonly used as a guideline for maintaining good indoor air quality in homes, offices, and public spaces.

  2. Offices and classrooms: In office spaces and classrooms, a common guideline is to maintain CO2 levels below 1000 ppm. This is because higher CO2 levels have been found to lead to decreased cognitive performance and reduced productivity.

  3. Workplace environments: Some workplaces are covered by ASHRAE or OSHA guidelines that mandate what the permissible CO2 limit over a 15 minute time limit or an 8 hour workday can occur.

  4. Building codes and standards: Different countries and regions have specific building codes and standards that dictate acceptable indoor CO2 levels. It's essential to check the local regulations for compliance.

In summary, keeping indoor CO2 levels within the acceptable range helps ensure good indoor air quality and the well-being and comfort of occupants.

Why do we measure CO2?

CO2 is often measured in indoor environments to quickly serve as an indication if additional ventilation is required. Because CO2 is a known indoor pollutant, too much CO2 can also affect overall employee performance, productivity, and overall health. 

When it comes to CO2 in the workplace, extreme levels of carbon dioxide exposure can create negative health effects particularly in enclosed spaces such as restaurants, breweries, beverage industries, agriculture facilities, laboratories, and many others. Overall, by measuring carbon dioxide in indoor areas you can have control over home, office, and workplace health and safety.

What is an unhealthy level of CO2?

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends an 8- hour TWA Threshold Limit Value (TLV) of 5,000 ppm and a Ceiling exposure limit (not to be exceeded) of 30,000 ppm for a 10-minute period. A value of 40,000 ppm is considered immediately dangerous to life and health (IDLH value).
Click the links below to see each organization's safe carbon dioxide levels and exposure limits:

What does high CO2 level exposure feel like?

Here's what it may feel like to be in an environment with high CO2 levels:

  1. Stale air: Rooms with high CO2 levels often feel stuffy and lacking in fresh air. This sensation occurs because CO2 accumulates when there is insufficient ventilation to bring in fresh outdoor air.

  2. Difficulty breathing: Some individuals might experience slight breathing discomfort or shortness of breath in areas with elevated CO2 levels. This is especially true for those with respiratory conditions or sensitivities.

  3. Drowsiness and fatigue: In environments with high CO2, people may feel more tired or experience difficulty staying alert. This can result in reduced productivity and concentration levels.

  4. Headaches: Prolonged exposure to elevated CO2 levels might trigger headaches in some individuals.

  5. Poor concentration and cognitive function: High CO2 levels have been associated with reduced cognitive abilities and impaired decision-making.

  6. Increased heart rate: In some cases, elevated CO2 levels may cause a slight increase in heart rate, particularly in sensitive individuals.

  7. Nausea and dizziness: In extreme cases of poor indoor air quality with very high CO2 levels, some people may experience nausea, dizziness, or other discomforts.

Example of a High CO2 level Incident

At CO2Meter, our own office encountered an actual CO2 incident and we wanted to share our story with others to provide further perspective on what to do should a potential CO2 leak occur and how CO2 monitors serve their purpose in being life-saving equipment.

It's important to know, that no emergency or medical personnel were dispatched to CO2Meter that morning. No employees were injured. But, thanks to the many leak detectors in our office, the CO2 alert warned our staff of potentially dangerous CO2 levels instantly. And yes, even the "gas detection people" can have an incident.

Here's what happened

Our technicians were studying the effects of extremely low temperatures on carbon dioxide sensors. By using dry ice (the solid state of carbon dioxide) they were able to push the temperature of the sensors and the air they were measuring down in order to test changes in accuracy.

After finishing their testing for the day, the techs placed the dry ice samples in the company refrigerator for temporary storage. Bad idea.

The first person to enter the building the next day heard the CO2 alert warning employees of dangerous CO2 levels. All the CO2 detector alarms in the building were signaling a problem. The LCD readout on the alarm nearest the door indicated the CO2 level was 1,500 ppm – safe but noteworthy.

While CO2 levels above 3% (30,000 ppm) are dangerous and would require the building be evacuated, 1,500 ppm only indicated a small problem. However, any CO2 level above 400 ppm in an unoccupied building was still cause for an alarm.

While several rooms showed elevated levels of CO2, none were unsafe to enter. All the outside doors were opened to ventilate the building. But it wasn’t until the first person opened the refrigerator to store their lunch that the CO2 levels jumped up again.

The staff realized it was the dry ice in the refrigerator’s freezer that was off gassing CO2. Our techs hadn’t realized that while the typical temperature in a freezer is 0 degrees Fahrenheit or -18 degrees Celsius, the freezing point of carbon dioxide is -109.2 degrees Fahrenheit, or -78.5 degrees Celsius. The dry ice was melting in the “warm” freezer.

Actually, the term melting isn’t quite accurate. As a solid block of CO2 warms it sublimates, turning directly into gas, rather than melting into a liquid. Other examples of solids that sublimate are iodine, arsenic, naphthalene (what mothballs are made of) and solid air fresheners. While water normally melts into a liquid, it can sublimate in special conditions of low temperature, low humidity and dry winds.

We were all happy that no one was injured and thankful that our devices worked as intended. As it turns out, even “the CO2 experts” can have a leak once in a while.

The Best CO2 Level Indoor Air Quality Monitors

 Best Carbon Dioxide Indoor Air Quality Monitor

CO2 Meter Indoor Air Quality Monitor (RAD-0302)

Our pick for the best air quality monitor is the IAQ Mini CO2 Monitor. This device can monitor indoor air environments by measuring CO2, Relative Humidity and Temperature from a sleek LED Display. The device provides information in an organized and user-friendly way; allowing the user to measure air instantly and modify ventilation as needed.

The addition of the 3 emotions and traffic light indicators on the main display screen also makes it very easy to view indication of poor, moderate, and good CO2 levels in any indoor environment.

For more information in indoor air quality monitoring, CO2 levels indoors, or indoor air quality detectors - please visit our contact us or call us at 877-678-4259.


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