General ventilation and air quality
Good air quality in the workplace is crucial for employee well-being and productivity. The task of general ventilation is to remove polluted air that can have a negative effect on health. General ventilation is used where air pollution mainly comes from people, building materials and furnishings.
Ventilation means that the polluted indoor air is replaced with fresh outdoor air. If the outdoor air is polluted, it may need to be filtered before being supplied to the premises.
General ventilation is used where contaminants are spread throughout the premises
General ventilation is used where the entire premises need to be ventilated, where air pollution mainly comes from people, building materials and furnishings. The contaminants can be body odours, perfumes, skin particles, dust, pollen, allergens from animals and various chemical contaminants. Typical premises include offices, schools, etc., where employees mainly perform their tasks with low intensity while sitting.
In such premises, only general ventilation is needed. By considering the air temperature and speed when placing supply and exhaust air, the entire premises can be ventilated.
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The air must be supplied to the premises in such a way that it does not cause draughts that could have a negative effect on health. It is also necessary to preheat the supply air in winter. Fan-controlled ventilation is normally needed therefore to provide sufficient airflow without creating troublesome draughts, and to be able to preheat the air.
The illustration shows supply and exhaust air as well as diffuse pollutants in an office.
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General ventilation is needed even when there is process- or protective ventilation in a room. This is needed so as to take care of the pollutants from the processes that the process ventilation does not capture, as well as the pollutants emitted from people and building materials.
Adjust the airflow according to the activity
In sedentary occupations such as in schools and offices, ventilation flows should be at least 7 litres of fresh outdoor air per second per person plus at least 0.35 litres per second per square metre of floor area.
The first airflow is needed so that most people accept the pollutants and odours that come from people. The second flow, of 0.35 litres per second per square metre of floor area, is needed to ventilate away pollutants coming from building materials and furnishings.
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By measuring the carbon dioxide content in a room, it is possible to get an idea of whether the amount of outside air supplied is sufficient to ventilate the pollutants. During a work shift or a lesson at school, the level of pollutants and carbon dioxide coming from the people in the room increases.
If both the number of people and the ventilation airflow are constant, the levels of pollutants and carbon dioxide will stay at an equilibrium level. In a school, where people sit relatively closely together, that level is around 1,000 ppm (one thousand parts per million) of carbon dioxide.
If the people in the room increase their physical activity, they will emit both more pollutants and more carbon dioxide. A higher outdoor air flow is then needed to ventilate the pollutants.
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Provisions on outdoor airflow in the Swedish Work Environment Authority's provisions and general guidelines (AFS 2023:12) on the design of workplaces apply provided that the ventilation is also effective. The carbon dioxide content in the air where there are people depends on the efficiency of ventilation.
Mixing ventilation is effective
Mixing ventilation means that the supply air dilutes the polluted room air. If there is complete mixing ventilation in the room, the carbon dioxide content in the occupied zone will be the same as in the exhaust air. The so-called air exchange efficiency is then 50 per cent. The air exchange efficiency should be at least 40 per cent for the ventilation to be called effective.
If the carbon dioxide level is high despite high airflow, it may be because the supplied air is poorly dispersed. This in turn may be due to a "short circuit", meaning that a large part of the supplied outdoor air goes directly out with the exhaust air without benefiting the room.
It may also be because the supply air and exhaust air vents are too close to each other or that the supply air is not supplied at a sufficient speed. High levels of carbon dioxide can also be because the supplied air is so warm that it rises towards the ceiling and never sinks into the occupied zone. The air exchange efficiency will then be low.
To solve the problem of low air exchange efficiency, outdoor air can be supplied at floor level at a slightly lower temperature than the room air. The polluted, warmer air will then rise and end up in a layer under the ceiling. If the exhaust air vent is also up by the ceiling, the air exchange efficiency can be higher than 50 per cent.
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During the time that work is in progress in the workplace, the air quality must be satisfactory. It is therefore important to start up the ventilation well in advance before work begins for the day. At least one hour of ventilation is normally needed to remove the pollutants that have accumulated overnight.
It is also a good idea not to turn off the ventilation completely at night when work is not in progress. It can continue to run, but with reduced flow.
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After new construction or interior renovation of a workplace, ventilation should run continuously for the first year to ventilate contaminants from building materials, furnishings and paints. Only then can you start to lower the airflow when the premises are not in use.
The employer is responsible for the risks of poor ventilation
As an employer, you are responsible for reducing risk from poor ventilation, just as you are responsible for all aspects of the work environment. You must be familiar with the Work Environment Act and other work environment regulations.
Get a better work environment through working systematically
As an employer, you must manage the work environment systematically, so as to improve it. Our provisions for systematic work environment management apply to all employers – regardless of the activities or the risks that you and your employees could be exposed to.
Employees and safety representatives are important for a good work environment
Employees and safety representatives have an important role in work environment management. As an employer, you must give all employees the opportunity to participate in work environment management. For example, you can let employees suggest measures or provide feedback on measures you have implemented.
Employees' participation in work environment management
As an employee, you must participate in work environment management and participate in implementing the measures needed to achieve a good work environment. You must follow the employer's instructions. You must also report to your employer or your safety representative if the work involves immediate and serious danger to life or health.
Last updated 2025-11-26