Carbon dioxide (CO2) is present in every environment around us. Detection devices are available to deal with this pollutant in enclosed spaces. Since COVID-19, this subject has come up more and more. A containment index called “ICONE” was created to execute the appropriate air renewal strategies according to the intensity of the index.

In this article, you’ll find a quick reminder of the basics of CO2, what the “ICONE” index is, and the thresholds that derive from it. To conclude, you’ll find our solutions for dealing with carbon dioxide in a room.

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Published on 8 January 2024

CO2 and the “ICONE” containment index

In this article:

A quick reminder of the basics

Carbon dioxide is an odorless, colorless gas invisible to the naked eye. Unlike carbon monoxide, CO2 is non-toxic to the human body. It also plays a crucial role in maintaining the Earth’s temperature. Carbon dioxide emissions have risen in recent years. They are due in particular to the excessive use of fossil fuels.

Depending on the amount of CO2 inhaled, various symptoms are experienced. They vary according to three criteria:

  • Exposure time
  • The amount of CO2 in the air
  • The person’s state of health and sensitivity

CO2 is measured in Parts per Million (PPM). Low carbon dioxide levels in the home mean healthy air. On the other hand, if this level is too high, it can have an adverse effect on a person’s health. It should be noted that, because of the increase in respiratory rate during physical effort, symptoms appear more quickly.


How to avoid carbon dioxide

In enclosed spaces, there are a few things you can do to limit your exposure to CO2. They will help you improve Indoor Air Quality:

  • Insulate your home as well as possible
  • Get a direct-reading CO2 sensor
  • Ventilate premises by opening doors and windows for at least 10 minutes a day
  • Limit consumption of fossil fuels such as natural gas, oil and coal
  • Use energy-efficient heating and air-conditioning equipment

In any environment, CO2 travels both indoors and outdoors. Its sources are numerous, such as :

  • Wood, oil, gas or electric heaters
  • Appliances and household equipment
  • Tobacco smoke
  • Fossil fuels, agriculture and human activities

One of the best ways to prevent CO2 in confined spaces is with a direct-reading detector. It is capable of monitoring the level of containment in the air.

ICONE CO2 containment index

The ICONE index (Indice de CONfinement d’air dans les Ecoles) is a benchmark for assessing indoor air confinement. It is divided into six categories ranging from 0 (no containment) to 5 (extreme containment). The average concentration in an enclosed space, calculated by the CO2 sensor, determines the containment index. In fact, the carbon dioxide sensor and the ICONE index are one and the same. The higher the air concentration, the more confined the air, so the figure is higher. In this case, the air is polluted and needs to be renewed. Consequently, a low CO2 level will bring the index closer to 0.

It is calculated over a period of 4.5 non-consecutive days in order to be more precise about the situations observed. What’s more, only the usual occupancy conditions are recorded, to avoid taking into account exceptional occupancy situations.

In some elementary classes, values of 4 (very high containment) and 5 (extreme containment) can be found. For example, a value of 5 indicates peak CO2 concentrations in excess of 4,000 ppm. It also corresponds to average occupancy values above 2,000 ppm.

Depending on WHO and ANSES regulations, thresholds may differ from one country to another. In France, regulations require an ICONE index of less than or equal to 1.5, i.e. 1500 ppm, for ERP (Etablissements Recevant du Public) buildings. In addition,ANSES recommends keeping CO2 levels below the 1000 ppm threshold.


Carbon dioxide thresholds

Regulations require ERP to monitor Indoor Air Quality. It is all the more necessary to examine this closely in schools and other facilities catering for a young public. Children are the most vulnerable to air pollutants because their immune systems are not fully developed to cope with them.

CO2 detectors are capable of measuring pollution levels in a closed environment over a wide range. The latter varies between 400 and 5,000 ppm. Thanks to on-board technology, you’ll be able to see whether your indoor air is healthy. This will enable you to implement corrective actions to improve Indoor Air Quality.

It can be difficult to interpret thresholds and their effects. To make things easier for you, here’s a quick summary:

  • <800 ppm: low CO2 content. It corresponds to a containment index of 0. No health risk
  • >800 ppm: CO2 content is average and is classified in categories 1 to 2. Symptoms such as fatigue, headaches, loss of concentration or drowsiness are possible.
  • >1500 ppm: high CO2 level. The containment ICONE is upgraded from category 2 to 3. More serious effects include dizziness, sleep disorders, nausea and breathing difficulties.

When the CO2 level exceeds 1700 ppm, the benchmark changes to 4 or 5. In this case, it is imperative to ventilate the premises immediately to reduce the concentration and avoid endangering the occupants of a room.

These thresholds are general indications. In fact, the consequences vary according to the type of individual, his or her sensitivity and the space in which he or she evolves.


Nexelec solutions help you renew the air at the right time

Nexelec offers a wide range of detectors capable of measuring and analyzing Indoor Air Quality. CO2 sensors are designed to make your life easier. On-board technologies allow you to precisely analyze the CO2 level in the room. The precision of the data collected helps you to act accordingly.

Connected, they offer reliability and stable connectivity. What’s more, CO2 thresholds can be configured in our Nexelec TOUCH application. The latter uses NFC technology to personalize carbon dioxide thresholds. The application alerts you when the rate becomes too high. Nexelec solutions also enable you to detect a wide range of indoor pollutants, as well as temperature and humidity.


Since the COVID-19 pandemic, CO2 concentration in confined spaces has been a major concern. The “ICONE” containment index has been developed to help you implement appropriate air renewal strategies based on the CO2 concentration measured. It is important to keep CO2 levels below regulatory thresholds. These indicators are all the more important in schools and ERP. Nexelec’s CO2 detectors and application offer an effective way of monitoring and improving Indoor Air Quality. Measures help you contribute to the health and well-being of occupants in schools and other facilities.