In brief
In crowded offices and meeting rooms, the carbon dioxide level is a practical indicator of whether ventilation is adequate; it rarely reaches dangerous levels itself, but as it rises complaints of headache, fatigue and poor concentration increase. The legislation requires sufficient fresh air and annual maintenance of the ventilation system. Worker complaints should be recorded by the workplace physician by place and time and assessed together with measurements and checks of the installation.
Why is office indoor air quality an OHS issue?
It is 3 p.m., and twelve people have been discussing the budget for two hours in a meeting room whose windows do not open. Some complain of headaches, others of drowsiness; someone says "the air conditioning is on but the air still feels heavy". This picture is the most typical form of an indoor air quality problem in offices. There is no toxic substance involved; the air people are breathing is simply not being renewed fast enough to meet the room's fresh air needs.
Offices are usually in the less hazardous class, but the air quality obligation is independent of the hazard class. Annex 1 of the Regulation on Health and Safety Measures in Workplace Buildings and Annexes requires the following for enclosed workplaces:
- Sufficient fresh air for workers' needs; the working method, number of workers and the work done are taken into account in determining the air volume (item 15),
- If mechanical ventilation is used, the system must be in working order at all times; maintenance, repairs and filter changes must be carried out annually by competent persons (item 17),
- Air flow must not disturb workers or create sudden temperature differences (item 18).
These provisions give no numerical value; adequacy is demonstrated by the workplace's own measurements and observations.
Office CO2 level: what does it measure, and how is it read?
People release carbon dioxide into the air they breathe. In a room where the air is not diluted with fresh air, the CO₂ level rises with the number of people and time. Office CO2 level is therefore a practical indicator of whether ventilation is adequate. The CO₂ level in outdoor air is around 400 ppm.
There is no binding CO₂ value for office comfort in the legislation. In Annex 1 of the Regulation on Health and Safety Measures in Work with Chemical Agents, the 8-hour occupational exposure limit value for carbon dioxide is 5000 ppm; this value is far above office comfort and is not a target for offices. In practice, around 1000 ppm is used as a common threshold indicating that ventilation is starting to become inadequate.
| Reading | Practical interpretation | What to do |
|---|---|---|
| Close to outdoor air (about 400–600 ppm) | Fresh air is sufficient | Continue monitoring |
| Approaching 1000 ppm | Ventilation is starting to fall short for the number of people | Increase the fresh air flow rate or intermittent ventilation |
| Clearly above 1000 ppm | Ventilation is inadequate, complaints are to be expected | Examine occupancy and the system |
These ranges are not legal limits but interpretations that help decision-making. When measuring, pay attention to the following:
- The right instrument: CO₂ meters with infrared (NDIR) sensors measure actual CO₂. Some cheap "air quality" devices estimate CO₂ from other gases; their values may be misleading.
- The right place: At the head height of a seated person, at a point where no one's breath reaches directly, away from windows and supply diffusers.
- The right time: At the hours when the room is fullest; at the start and end of a meeting. Devices that record throughout the day give the best picture.
For temperature, humidity and air velocity measurements, which should be assessed together with thermal comfort, see our article on thermal comfort measurement. If a formal workplace measurement is needed, we plan it with authorised laboratories.
Meeting rooms and crowded offices: why does CO₂ build up?
Most office ventilation problems come down to a few common causes:
- Air conditioning does not bring in fresh air. Wall-mounted split units and many fan-coil units cool or heat the air in the room and return it; they do not take in outside air. "The air conditioning is on" does not mean ventilation is taking place.
- Design capacity is exceeded. Twelve people regularly gather in a meeting room designed for six.
- The fresh air damper has been turned down. The outside air ratio of the central system was lowered to save energy and then forgotten.
- The door is closed and the window does not open. Especially in buildings with glass facades, windows are never opened.
- Changes to the space. An open-plan office has been divided into small rooms with partitions, but the diffusers have stayed where they were.
The solution is to find the cause: adding a fresh air diffuser to the meeting room, demand-controlled ventilation operated by a CO₂ sensor, a short ventilation break between meetings and writing the room's capacity on the door are simple but effective steps.
Air conditioning maintenance and filters
Air conditioning maintenance is the second pillar of indoor air quality. A clogged filter reduces air flow; a dirty condensate tray and humidifier create a suitable environment for microorganisms to grow. Item 17 mentioned above requires maintenance and filter changes to be carried out annually by competent persons. In addition, Annex III of the Regulation on Health and Safety Requirements for the Use of Work Equipment subjects ventilation and air conditioning installations to an annual periodic inspection and states that the installation design will be requested during this inspection.
Ask for the following to appear in the maintenance record:
- The class of the filters and the date they were changed,
- Cleaning of condensate trays and drainage,
- The location and cleanliness of the fresh air intake; the intake should not be close to an exhaust outlet, a car park ramp or a smoking area,
- Adjustment of fans, dampers and the control system,
- Disinfection of any humidifiers and cooling towers.
Cooling towers and hot water systems carry a legionella risk; on this topic, see our article on legionella risk. When assessing periodic inspection reports, our article on how to read a periodic inspection report will guide you.
Sick building syndrome and assessing complaints
Sick building syndrome is when symptoms such as headache, irritation of the eyes, nose and throat, fatigue and difficulty concentrating seen in some of the people working in a building are linked to the time spent in the building without being attributable to a specific disease, and ease on leaving the building. It is distinguished from "building-related illnesses" with a known cause, such as Legionnaires' disease.
The workplace physician assesses complaints in the following order:
- Record: Who, which symptom, which room or floor, what time of day? A simple questionnaire form is enough.
- Pattern: Are symptoms concentrated in a particular area? Do they ease in the evening and at weekends?
- Measurement: CO₂, temperature and humidity are recorded throughout the day in the areas complained about.
- Source investigation: New furniture, carpets or paint, heavy printer and photocopier use, cleaning chemicals, signs of damp and mould.
- Installation check: Maintenance records, filter condition, fresh air ratio.
| Symptom pattern | Possible cause | First check |
|---|---|---|
| Headache and drowsiness increasing in the afternoon | Insufficient fresh air | CO₂ record, number of people |
| Dry eyes and throat, worse in winter | Low humidity, high temperature | Humidity and temperature measurement |
| Odour and irritation in a newly occupied or refurbished area | Volatile substances from furniture, carpets, paint | Increasing ventilation, identifying the source |
| Coughing and sneezing in a particular room | Damp, mould, dirty installation | Visual check, maintenance record |
The results are entered into the risk assessment and feedback is given to the workers who complained; questionnaires without feedback go unanswered next time. For other health aspects of screen work, see our article on working with display screen equipment.
A short checklist for the office manager
- Is the capacity of each meeting room written on the door?
- Is the fresh air source of the meeting rooms known?
- Is the last maintenance and filter change more than a year old?
- Is there an annual periodic inspection report for the ventilation and air conditioning installation?
- Are complaints recorded and passed on to the workplace physician?
- Has CO₂ been recorded for a week in the two most crowded rooms?
For an example assessment, see our article on the office risk assessment example. Through our workplace physician and risk assessment services, we assess complaints by place and time, plan measurements with authorised laboratories where needed and link the results to the action plan. For other risks in office and retail workplaces see our office and retail page, and to see your obligations, our OHS obligation calculator.
Frequently Asked Questions
Is there a legal limit for CO₂ in the office?
There is no binding value for office comfort. The 5000 ppm in the Regulation on Chemical Agents is the 8-hour occupational exposure limit and is not a target for offices. In practice, around 1000 ppm is used as the threshold indicating that ventilation is becoming inadequate.
How often should the air conditioning filter be changed?
The legislation requires maintenance and filter changes of mechanical ventilation systems to be carried out annually by competent persons. In buildings with a high dust load, the more frequent change interval recommended by the manufacturer should be applied.
Is sick building syndrome an occupational disease?
Sick building syndrome is not a single disease but a set of building-related symptoms occurring together. If a specific agent, such as legionella or a chemical exposure, is found to underlie the symptoms, the assessment is made according to that agent.
Is opening the window an adequate method of ventilation?
It may be adequate in small rooms with few people. In crowded offices and meeting rooms, window ventilation is irregular and is not used in winter; mechanical fresh air supply is needed in these areas.
A physician assigned for the time your hazard class requires: pre-employment and periodic examinations, fitness-for-work reports and health surveillance.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.