<img height="1" width="1" style="display:none" src="https://www.facebook.com/tr?id=1843732482513221&amp;ev=PageView&amp;noscript=1">

When is it necessary to purify indoor air?


Indoor air should be purified if the quality of indoor air causes symptoms to someone staying in the premises. Typical symptoms include, for example, stuffiness of the nose, redness and itchiness of the eyes, headaches and even symptoms of asthma.


Constant exposure of employees to symptom-producing impurities often makes the situation worse and leads to absences from work that can be very expensive for the employer. Symptoms caused by indoor air problems are often treated with asthma medication or simply by transferring the person with symptoms to other premises. However, asthma medication only treats the symptom and not the cause, when the cause should naturally be eliminated as well.


Studies have shown that even a single substance or very small concentrations of particulate impurities or their combinations may be harmful to health.

As a result, health authorities, such as Valvira* (the Finnish National Supervisory Authority for Welfare and Health), have determined threshold values for several harmful substances and the concentration of respirable particles (PM10) in indoor air.


People are the best indicators of indoor air quality


The best indicators of indoor air quality are people who spend most of the time indoors. The human nose can smell several substances – even in very small quantities.  The quality of indoor air can also be measured, providing reliable data concerning the concentration of several particles.


The results contain terms, such as TVOC, MVOC and VOCs, and the unit is commonly µg/m3. VOCs are volatile organic compounds, and MVOC stands for microbial volatile organic compounds.  TVOC  stands for total volatile organic compound.


For example, in Finland, Valvira has set the following action limits* for various compounds:


  • 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (TXIB) 10 µg/m3.
  • 2-ethyl-1-hexanol (2-EH) 10 µg/m3.
  • No naphthalene odour is allowed, and the action limit is 10 µg/m3.
  • The action limit for styrene is 40 µg/m3.
  • The concentration of respirable particles (PM10) in indoor air should not exceed 50 µg/m3 during a 24-hour measurement.


There are several types of VOCs, and there is no clear evidence that any one substance is harmful to health. Several harmful substances as well as fine particles from combustion that travel from outdoors to indoors or fine particles from the structures of the building often co-exist in the air, and their combined effect causes symptoms to people who stay in the premises.

How to temporarily restrict conditions that have an adverse effect on health?


In Valvira guideline12/2018** on controlling the conditions in schools and daycare centres, and preventing and investigating adverse health effects, Senior Officer Pertti Metiäinen gives very detailed instructions for protecting the people against harmful substances during investigations. He writes, for example, that “air purifiers can be used to reduce the impurities in the air” and that “air purifiers can be used, mainly temporarily, before or during repairs to protect the people in adjacent premises or after repair work when waiting for the conditions to stabilise.”


Air purifiers as first-aid in conditions that cause adverse health effects


Air purifiers are an efficient first-aid when investigating the source of indoor air problems, preparing repair plans and even during repair work. It should be noted, however, that air purifiers don’t eliminate the cause of the problem and repairs might be necessary. Air purifiers allow extra time for repair projects if several premises in the municipality are awaiting large-scale renovations at the same time. It might not be possible to repair everything at once, let alone to have the money for it. Air purifiers can be used to protect problem sites that are waiting for a renovation until the work in more urgent sites have been completed.



*Asumisterveysasetuksen soveltamisohje Osa 3 Asumisterveysasetus 14-19 Ohje 8/2016 nro 2731/06.10.01/2016 (Implementing measures for the Decree on Health-related Conditions of housing, part 3). (pp. 3 and 9).

** Ohje koulun ja päiväkodin olosuhdevalvontaan, terveyshaitan ennaltaehkäisemiseen sekä selvittämiseen Ohje 12/2018 nro 13377/2018 (p. 40) (Guideline on controlling the conditions in schools and daycare centres, and preventing and investigating adverse health effects).


Download our free guide to learn more about good indoor air quality: