Permissible CO2 Content in Rooms

There is increasing talk about how elevated carbon dioxide levels in the air negatively affect human well-being. But how do you determine air quality? What measures should be taken to improve it? What is the acceptable CO2 level indoors? We will discuss this, starting with how carbon dioxide affects the human body and why it is dangerous.

Why Carbon Dioxide is Dangerous for Humans

We inhale oxygen and exhale carbon dioxide, which is well known. In one hour, an adult at rest consumes about 25 liters of oxygen and exhales approximately 22 liters of carbon dioxide, and during exercise or active movement, this amount increases to 36 liters. The air we exhale contains 100 times more of this component than the atmosphere. However, many do not realize that CO2 accumulates in poorly ventilated rooms, altering the composition and quality of the air. Essentially, it is a byproduct of our vital activity, and when we are indoors, we are forced to breathe it again. Polluted air causes a deterioration in people’s well-being. The most common "symptoms" are drowsiness, apathy, loss of concentration, and headache.

Effects of Carbon Dioxide

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Carbon dioxide is an integral part of the air mixture, but its concentration outdoors is low – about 400-450 ppm (parts per million), which corresponds to 0.04% by volume. The more industrial enterprises located in a residential area, the higher the concentration of pollutants and carbon dioxide. Therefore, such areas typically have elevated standards, while zones with favorable environmental conditions have lower ones. The indoor CO2 level standard exceeds outdoor values by about 1.5 times, i.e., up to 600 ppm.

A concentration of 800 ppm is already considered unsafe, and at 1000 ppm, or 0.1% by volume, the first signs of "poisoning" appear (unexplained lethargy, difficulty breathing). However, these values are still within the norm: exceeding sanitary standards is considered at levels above 1400 ppm. At such levels, it becomes difficult to concentrate on tasks at work and hard to fall asleep normally at home.

Critical values are above 3000 ppm (0.3%). In this case, signs of oxygen deprivation develop rapidly, nausea occurs, and pulse rate increases.

Symptoms of Carbon Dioxide Exposure

Numerous studies conducted in Asian and European countries show that indoor CO2 levels (ppm) indeed affect the well-being of students, residents, and workers. Among them:

1. Indian scientists from Kolkata determined that CO2 is a dangerous toxin that at elevated concentrations causes biochemical changes up to the cellular membrane level and provokes acidosis. They studied about 600 people from industrial areas and suburbs and found that those living in polluted atmospheres have on average 60% higher bicarbonate levels in their blood serum.
2. British scientist Robertson calculated that adverse changes in the human body begin at CO2 levels around 426 ppm. More significant excesses provoke short-term overexcitement, persistent anxiety, and reduced desire for physical activity.
3. A group of Finnish scientists led by Olli Seppanen involved over 30,000 people in their experiment and found that in offices where CO2 concentration does not exceed 800 ppm, people work with greater concentration, complain less about headaches, and suffer less from respiratory infections.
4. In Italy, scientists (members of the European Commission DG SANCO under the "Health Effects of School Environment" program) studied the effect of CO2 on children (experiment conducted in 2006) and found that exceeding 1000 ppm doubles the risk of rhinitis in children, and dry cough occurs 3.5 times more often. Children who spend long periods in polluted rooms have more vulnerable nasopharynxes.
5. Korean specialists studied the link between asthma and CO2 concentration in apartments where sick children live. They found that CO2 levels directly affect the number of attacks.
6. The audit group "KPMG" (Netherlands) and scientists from Middlesex University (UK) conducted an experiment among office workers. They proved that exceeding 800 ppm reduces attention by 30%, at 1000 ppm people begin to experience headaches, at 1500 ppm most (80%) feel fatigue, and at 2000 ppm 60% of workers could not concentrate on their usual tasks.

All these studies more or less confirm that stuffiness, dizziness, decreased productivity, and other general malaise symptoms arise not from lack of O2 but from excess CO2.

When is Carbon Dioxide Level Monitoring Necessary

There are 4 classes of air quality (according to GOST R EN 13779):

• IDA 1 or high quality, less than 400 ppm
• IDA 2 or medium quality, about 400-600 ppm
• IDA 3 or acceptable, from 600 ppm to 1000 ppm
• IDA 4 or low, above 1000 ppm

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It is impossible to reduce carbon dioxide emissions: it is produced by breathing, comes from outside (especially if windows face a highway), is released when a fireplace is burning, or when a gas stove, boiler, or water heater is operating.

However, it is possible to monitor the amount of CO2 in a room using special sensors and provide timely ventilation, preventing the worsening of negative processes and not harming people's health. Such measuring devices are especially necessary in rooms where children study, asthmatics are treated, or technical processes requiring increased concentration from employees take place. It is clear that these values cannot be determined "by eye," and people have different sensitivity thresholds.

Sensors are usually integrated with ventilation system equipment. It is important that the ventilation has sufficient capacity. Standards prescribe the following typical air exchange rates: for conference halls and classrooms, 25.5 m³/h of fresh air; for restaurants and offices – 34 m³/h; for hospitals and residential premises – at least 42.5 m³/h per person.

Carbon Dioxide Standards in Residential Premises

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Building standards for CO2 concentration apply to residential premises according to GOST 30494-2011, but physiologists have differing opinions (they believe the standards are too high and do not actually ensure safety). The following levels of "pollution" are distinguished:

• Atmospheric air, good energetic well-being: 400-600 ppm by standards and 300-400 ppm according to physiologists;
• Normal quality: 800 (600);
• Medium quality – 800-1000, but in practice at the upper threshold every second person feels sluggishness, stuffiness, drowsiness;
• Permissible norm 1000-1400. These values are considered maximum allowable, but in practice many people already experience reduced attention, impaired perception and information processing ability, breathing difficulties, and dryness of the nasal mucosa;
• Poor air quality – above 1400 – causes strong fatigue, people become unmotivated, cannot concentrate on routine tasks, and have difficulty falling asleep. When exceeding 2000 ppm, 70% of people make mistakes at work.

Standards in Schools

The higher the carbon dioxide level in the classroom, the harder it is to absorb information and cope with the academic load. In the USA, recommendations state that CO2 concentration in educational premises should not exceed 0.06%. In Russia, current standards allow a volume fraction of up to 0.08%. In practice, such values are rarely met – there may be a 2- or even 3-fold excess, causing sweating, nasal congestion, and high fatigue. Sealed plastic windows significantly worsen natural ventilation: in a classroom with 25-30 students, carbon dioxide levels double the norm in just half an hour, i.e., even before the lesson ends. Therefore, it is recommended to ventilate the room during every break (if a comprehensive ventilation system upgrade is not possible).

Standards in Offices

Elevated carbon dioxide levels in offices cause the same problems as in schools: productivity decreases and the number of errors increases. According to SanPiN, acceptable levels range from 800 to 1400 ppm, but in practice signs of "overdose" appear already at 1000 ppm (0.1%).

In rooms with air conditioning, the problem only worsens. Cooled air feels comfortable, windows remain closed, but lowering the temperature does not reduce CO2 concentration. Therefore, it is important to install a special sensor, improve the ventilation system, and ensure that employee density complies with current building standards – from 4 to 6.5 m2 per person.

Conclusions

The problem with ventilation is most pronounced in apartments, office buildings, and children's educational institutions. It is exacerbated by significant discrepancies between building and sanitary-hygienic standards. While GOST allows CO2 levels up to 1400 ppm, physiologists consider 800-1000 ppm as the upper limit.

The situation is also strongly influenced by construction violations: insufficient ventilation, installation of plastic windows, and air conditioners without ensuring adequate fresh air supply. In rooms where people are constantly present and windows cannot be kept open continuously, CO2 control sensors and compact supply ventilation should be installed to consistently reduce carbon dioxide levels, preventing its harmful effects on health.