"WHO" Indoor Air Quality in Schools survey in Latvian schools for the 2015/2016 school year

From 14 September 2015 to 8 January 2016, the Health Inspectorate carried out a survey of indoor environmental quality, including indoor air quality, within the framework of the World Health Organisation (WHO) study "Indoor Air Quality in Schools". 14 schools took part in the survey: nine urban schools, two suburban schools and four non-urban (i.e. rural) schools. Three schools were surveyed in the Kurzeme region, three schools in the Zemgale region, four schools in the Vidzeme region, two schools in the Latgale region and two schools in Riga city and suburbs.

Pētījums "Skolu iekštelpu gaisa kvalitāte" apsekojuma rezultāti

Photo: StockPhoto.com, majaelpo.lv

The study was launched in Latvia in 2013 on the basis of the Declaration on Environment and Health adopted by the Parma Conference of European Ministers of Environment and Health on 11 March 2010 (hereinafter - the Parma Declaration) with achievable targets for a safe and healthy environment for children*. To achieve the objectives set out in the Parma Declaration, WHO developed a set of indicators that will reflect the quality of the school environment (especially indoor air) in European countries. The first study was carried out in Croatia and Albania. A similar survey has been carried out in the Baltic countries.

The survey has so far examined the following factors:

  1. The signs of mould and damp in some school rooms and their impact on indoor air.
  2. Carbon dioxide (CO2) concentrations in classrooms measured in indoor air.
  3. Access to, proper operation and maintenance of sanitation facilities in schools, and student satisfaction.

Mould and moisture measurements

The survey examined the presence of mould and damp in three classrooms in each school and in the sanitary facilities (toilets) provided for students. The signs of damp and mold were evaluated visually and by measuring the total area (m2) affected by damp using non-invasive diagnostic methods to measure the moisture content of the building materials.

In total, 49 classrooms were measured for humidity. No signs of mould were observed in any classroom. Minimal signs of moisture damage on surfaces of 0.7-2 m2 (of the total room area) were observed in three classes, and in one class slight moisture condensation on the window panes. In contrast, surface moisture measurements showed that all surfaces in 45 classes (92% of cases) were completely dry, while four classes (8% of cases) showed moisture in the area 0.7 - 41.7 m2 , including one class where the entire floor surface was damp (probably a consequence of a recent renovation).

In four classes (8% of cases) odors were detected: mold odor in one class, chemical odor (probably from the flooring) in one class and stale air odor in the remaining classes.

Moisture measurements were also carried out in sanitary facilities - a total of 118 toilets and 120 hand-washing facilities were surveyed. Four rooms (4% of the total) ranging from 0.5 to 1.5 m2 showed signs of mould, while 12 rooms (10% of the total) ranging from 0.3 to 3.5 m2 showed signs of moisture damage on surfaces. However, the moisture measurements of the surfaces showed that the majority (90%) of the surfaces were completely dry, with only 12 toilet rooms (10% of cases) ranging from 0.5 - 12.5 m2 showing moisture. The odours detected were typical of boys' toilets (15% of all rooms) and attributed to poor hygiene skills.

CO2 concentration measurements

 It should be noted that the CO2 concentration in a room is the most objective measurable indicator of the effectiveness of ventilation - sufficient fresh air supply, as the occupants are the main source of CO2. CO2 is released by human life processes. Indoors, CO2 levels range from 400 to 2000 ppm (ppm - parts per million - the ratio of the number of particles to the volume in which those particles are located), while outdoor air CO2 levels range from 350 to 450 ppm.

Indoor CO2 concentrations above 1000 ppm indicate insufficient ventilation and also that the room is not large enough for the number of school children. Thus, the higher the CO2 concentration in the indoor air, the greater the need for increased fresh air supply to the room. The amount of fresh air to be supplied in a given period of time depends on the volume of the room (m3), the number of people and the type of work to be done.

Poor ventilation in schools is associated with adverse health effects including general fatigue, increased risk of infectious diseases, restlessness at the desk, reduced work capacity, however CO2 concentrations of up to 5000 ppm are considered to be a health risk (Prill R., It should also be noted that an average CO2 concentration of 5000 ppm is considered to be the maximum occupational exposure limit (OEL)** in workplace air 1,2. Study (Satish et al., 2012) 2 shows that mental performance decreases at CO2 concentrations of 2500 ppm.

In each school, CO2 measurements were taken in three classrooms simultaneously and continuously during one week. In each classroom, on each day of the study, the teacher filled in a classroom occupancy diary, which included the start time of each lesson, the age and number of pupils (how many children were in the classroom during the lesson and how many during the break), and the type of ventilation (windows open, doors open). Three indoor air quality monitors with CO2 logging and data recording and storage function were used for CO2 measurements.

A total of 42 classrooms in 14 schools were surveyed. Of the 14 schools surveyed, seven have natural ventilation, five have natural ventilation combined with passive ventilation (air supplied through specially designed ducts and devices but without a mechanism to move the air) and seven have mechanical ventilation throughout the school building or in individual rooms (of these, one school has no provision for room ventilation through windows). Of the 42 classrooms surveyed, 26 have natural ventilation and 16 have mechanical ventilation.

The analysis of the CO2 concentration measurements showed that:

  1. CO2 concentrations in 28 classrooms (67% of cases) reached 1000 ppm and above in the presence of students (average concentrations during the 5 days of classes), indicating insufficient ventilation of the classrooms in question.
  2. In 14 classrooms (33%), ventilation was considered adequate because the CO2 concentration (the average concentration during the five school days) was below 1000 ppm when the students were present.

    It should be noted that the CO2 concentration in a room where people are present is variable and for simplicity can be compared to the colors of a traffic light - green (CO2 concentration up to 1000 ppm), yellow (1000-1500 ppm), red (>1500 ppm). The results of the school survey, grouped by traffic light colors (taking into account the average CO2 concentration during lessons over the five school days), are as follows:

    - green - good air in the classroom, no urgent ventilation - 33% of the time,
    - yellow - classroom air quality deteriorates, ventilation is needed - 48% of the time,
    - red - classroom air quality is poor, ventilation is urgent - 19% of cases.

  3. It should be noted that there are descriptions of the traffic light principle, for example in some classrooms in Germany, where students can monitor CO2 concentrations by observing the color changes in a device placed in the classroom and signaled by a traffic light that the room needs to be ventilated.
  4. According to observations and the class teachers' records in the classroom occupancy diary for the study, ventilation was provided during breaks and, in some cases, at a minimum during lessons (window open in one of the two positions provided for ventilation). The problem is that the classrooms are often occupied by pupils during breaks and therefore are not fully ventilated with at least two windows fully open.
  5. CO2 concentrations increased rapidly at the beginning of each day's activities when the students were in the classroom (one person is known to release 20-50 l of CO2 per hour, and this amount varies depending on age, weight and activity).
  6. CO2 concentrations are rising rapidly, both naturally and in mechanically ventilated rooms. The more people in the classroom, the faster the CO2 concentration rises and the higher the CO2 concentration.
  7. The CO2 concentration in the classroom increases in proportion to the number of students, as humans are the source of CO2 release, so it is important to maintain at least a minimum room area of 2m2 per student (79% of all classrooms in the study had the maximum room area for the number of students).

Access to sanitation facilities, proper operation and maintenance, student satisfaction

118 toilet facilities were surveyed in schools. In almost all (96%) of the toilet rooms, the equipment was in working order, all areas (walls, floors, toilets) were clean and tidy, waste bins were available 97% of the time, lighting was in working order 96% of the time, and toilet paper was available in all toilets. In 15% of the toilets (boys), there was an odour, mainly attributed to lack of hygiene skills - the water in the toilet bowl was not flushed.

According to the methodology of the study, the areas where students can wash their hands after using the toilet were examined. 120 such places were surveyed, next to or near to toilets. In all the facilities, the equipment (sinks and taps) was in working order, the rooms (walls and floor) were tidy, clean and waste bins were accessible. Almost all (98%) rooms had facilities for drying hands.

Recommendations for safe and healthy environment

  1. Schools with CO2 concentrations (measured while students are in the classroom) above 1500 ppm are advised to responsibly and carefully consider the measures to be taken to ensure fresh indoor air for students. Measures schools could take include increasing the frequency and duration of ventilation, thoroughly airing rooms without pupils present during breaks, and matching the size (volume) of the room to the expected number of children.
  2. In all schools, classrooms should be ventilated at the start of the school day, with opening windows and, if possible, doors wide open.
  3. In all schools, classrooms must also be ventilated at every break, for at least five to ten minutes (depending on the length of the break), with several windows wide open. Students should not be in the classroom during each break for safety reasons and because ventilation can create draft if doors and windows are open at the same time.
  4. During classroom time, the school corridors and recreation rooms should be ventilated (at least 10 minutes) by opening several windows wide.
  5. In all schools, all windows must be opened wide (for at least 10 minutes or more) to ventilate the classroom, even at the end of the school day when there are no students in the classroom. Doors can also be opened, but it is important to bear in mind that corridors also accumulate CO2 during the day, and if the corridor is not ventilated, the classroom also exchanges air from the corridor, which may have elevated CO2 levels.
  6. In classrooms with mechanical ventilation, where possible, adjust its operation to provide fresh air for the maximum number of students expected in the classroom.
  7. If possible, partial ventilation can be provided during the lesson if the window design allows it (windows open at a slight angle). However, there is no conclusive evidence that such ventilation has a significant effect on air quality, especially in crowded areas.
  8. It is recommended to organise the work in such a way that the classroom area is at least 2 m2 per pupil.
  9. Ventilation of sanitary and hygiene areas, including forced ventilation (when not occupied by students), is recommended to promote moisture removal and reduce conditions conducive to mold growth.
  10. It would be useful for schools to measure CO2 repeatedly or, if possible, regularly.

Please note that ventilating rooms soon after they have been occupied not only removes CO2, but also several organic and inorganic chemicals that are released into the room as a result of the human body's life processes (ammonia, mercaptans, skatole, indole, etc.), as well as microbes that are released when people breathe, talk, cough or sneeze. Subjectively, all these substances and micro-organisms create an unpleasant odour in the room. Ventilating the room at the end of the day prevents chemical and bacteriological contamination of the air during the night.

* The Parma Declaration's targets for a safe and healthy environment for children:

  1. Safe drinking water and sanitation at home, school, kindergarten (by 2020);
  2. A safe, healthy environment and opportunities to get to school and kindergarten on foot, by bike, etc. (by 2020);
  3. Healthy indoor environments for every child in schools and other children's facilities by meeting the World Health Organization's indoor air quality guidelines and making children's environments smoke-free (by 2015).

**AER - Occupational exposure limit value means the concentration of a chemical substance in the air of the working environment which, during the whole working time, working 8 hours per day (or for a different period, but not more than 40 hours per week), when applied intermittently or continuously to the body of a worker, does not cause in him or in his offspring somatic or mental illness or health abnormalities beyond the adaptability which are detectable immediately or at a later period by modern methods of investigation.


  1. Prill R.Why Measure Carbon Dioxide Inside Buildings. Washington State University Extension Energy Program. 2000
  2. Satish et al. Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance. USA:National Institute of Environmental Health Scieneces. 2012
  3. Eglīte M. Environmental health. Riga Stradiņa University. Riga: 2008, pp. 96, 240-246.
  4. World Health Organization. Parma Declaration on Environment and Health: http://www.euro.who.int/__data/assets/pdf_file/0011/78608/E93618.pdf

Article reprinted from the LV MoH Health Inspectorate homepage. Link to original source: https://www.vi.gov.lv/lv/pvo-petijuma-skolu-iekstelpu-gaisa-kvalitate-apsekojuma-rezultati-latvijas-skolas-20152016macibu-gada