Why ventilate interior spaces?

Numerous scientific studies have focused on the quality of the air in closed spaces, and in particular within the framework of professional spaces (offices, public places, schools, etc.). Most national laws have also integrated criteria on indoor air pollution, and on optimal temperature and humidity conditions, depending on the type of activity of the places and the characteristics of the indoor environment. . These criteria are often the basis for defining and adjusting the ventilation of the premises.

Air pollution: exterior and interior

The quality of outdoor air is measured by local or national authorities at different points in the territory. We measure the different constituents of outdoor air pollution:

Result of incomplete combustion of carbon compounds. This colorless and odorless gas is the cause of many household poisonings, often fatal.

Colorless, dense and toxic gas, the inhalation of which is strongly irritating. It is released into the Earth’s atmosphere by volcanoes and certain industries, as well as from the combustion of certain non-desulfurized oils, coals and natural gases.

Suffocating poisonous reddish-brown gas with a characteristic pungent pungent odor. A major pollutant of the Earth’s atmosphere produced by internal combustion engines (Diesel) and thermal power stations

The famous greenhouse gas. It irritates the eyes and lungs, and affects breathing capacity. Combined with oxides of sulfur and nitrogen, the effect is worsened, especially with prolonged physical exertion.

Particles suspended in the air, of natural origin or linked to human activity. They are categorized according to their size:

  • particles with an aerodynamic diameter greater than 10 micrometers are retained by the upper airways (nose, mouth)
  • PM10, so-called “breathable” 24 particles, include fine, very fine and ultrafine particles and can enter the bronchi
  • PM2.5 includes very fine and ultrafine particles and enters the pulmonary alveoli
  • PM1.0 includes ultrafine particles and can pass the alveolar-capillary barrier.

On average, we spend 80% of our time in closed places. While you might think that indoor air quality is better than outdoors, it’s actually quite the opposite!

The reason is simple. Indoor spaces are not sufficiently ventilated. Pollution is produced there and accumulates there.

Indoor air pollution and CO2 concentration

In addition to the pollution of the outside air trapped inside by a lack of ventilation, there are all the internal sources of air pollution, such as kitchen fumes and fumes, household products, paint, cosmetics, etc. the use of printers and other machines, dust, possible cigarette smoke if you are a smoker, candles and incense sticks …

If CO2 is not, strictly speaking, a pollutant. It is nevertheless dangerous at high concentrations. It is estimated to be fatal at a concentration of 3% (or 30,000 µm). But this concentration is almost impossible to achieve.

Numerous scientific studies have shown that measuring the CO2 concentration indoors gives a good approximation of the level of indoor air pollution. This is why most legislators have set indoor pollution criteria (and therefore ventilation rules) based on the measurement of the CO2 concentration.

Lack of ventilation and indoor air pollution

The consequences of poor indoor air quality are numerous:

  • Loss of concentration
  • Nausea
  • Headache
  • Nasal irritation
  • Difficulty in breathing
  • Dryness in the throat
  • Spread of respiratory viruses

In the workplace, this means LOSS of PRODUCTIVITY and INCREASED ABSENTEEISM.

At European level, a 2011 study (Promoting Actions for Indoor Healthy Air (IAIAQ), showed that 2 million citizens suffered from diseases linked to poor indoor air quality! According to another study (EEA – European Agency for Environment), air pollution caused the death of 400,000 people in 2016.

CO2 concentrations in ppm (part per million)

The concentration of CO2 in ambient air is measured in parts per million. In outdoor air, the level is generally between 350ppm and 500ppm, depending on the location. In general, the average value of 400 ppm is taken. Up to 800 ppm, the air quality is considered to be good. Above 1200 ppm, the air quality is considered poor.


National and local regulations on CO2 levels in business premises may vary. But in general, the recommendation is to keep the CO2 concentration below 900 – 1000 ppm.

Human presence (respiration) is one of the main sources of indoor CO2 production. It is therefore necessary to ventilate, all the more frequently as the number of people is high, and their activity is intense.

Coronavirus – COVID19

The risk of contamination with COVID19 (respiratory virus) is all the greater, in indoor spaces, as the virus concentration (viral load) is high. This concentration will increase with the lack of regular ventilation.

This is why we can use the measurement of the CO2 concentration to estimate the quality of ventilation, and therefore limit the risk of COVID19 contamination in confined spaces.

The right combination of Temperature - Relative Humidity

The ideal temperature in an enclosed space obviously depends on the type of activity taking place there. The same temperature is not necessary for static people, seated at a desk, and personnel in constant movement. There are also differences between summer and winter. It is important to properly define the comfort temperature.


Relative humidity indoors

Too dry air can cause throat irritation, and is not good for allergy sufferers. In addition, air that is too humid will encourage mold and the development of fungi, which will also pollute the ambient air.

The scientific and legal consensus is to maintain a relative humidity between 40% and 70%.



Ventilate, Ventilate!

Regular manual ventilation of the premises, 3 to 5 times a day, summer and winter, is essential, if mechanical ventilation (which renews the air) is not available. It is only by renewing the air that indoor pollution can be limited.

The frequency of ventilation will obviously depend on the size of the premises, the number of occupants, their types of activity and the production of pollutants inherent in the place concerned.

It is in this context that it is recommended to measure this air quality continuously, in order to ensure that the set thresholds are not exceeded.

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