Workplace ventilation

Last updated: 17 Jun 2024

Employers must ensure there is adequate ventilation in enclosed areas of the workplace. Well-ventilated buildings are more healthy and comfortable, and provide a more productive working environment. This guidance summarises the standards members can expect of their employers.

What is ventilation, and why is it important?

Ventilation is the process of bringing in fresh air from outside the building and removing indoor air. This process helps moderate internal temperatures and humidity, replenish oxygen, remove contaminants such as fumes or viruses, and create air movement which improves comfort.

Some viruses, such as COVID-19 and influenza, are spread by inhaling tiny saliva particles, or aerosols, which stay buoyant in the air and can travel large distances. A well-ventilated space reduces the concentration of viruses in the air and hence the probability of infection.

Ventilation systems and functionality can vary widely, and will often incorporate systems to heat and cool the building. Broadly speaking, buildings will utilise:

  • Natural ventilation, which relies on doors, windows and other openings such as trickle vents, air bricks or grilles to provide fresh air, or
  • Mechanical ventilation, which uses fans, ducts and control systems to move air into and out of rooms, or
  • A mixture of natural and mechanical ventilation, with either or both systems in different spaces.


What must employers do?

Regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992 states: “Effective and suitable provision shall be made to ensure that every enclosed workplace is ventilated by a sufficient quantity of fresh or purified air.”

Employers must consider whether ventilation in their enclosed workplaces is “effective and suitable” by carrying out a risk assessment. Because ventilation systems can be complex, employers’ assessments may require competent, professional expertise.

Where dust, fumes and vapours are produced, employers must carry out a COSHH risk assessment.

The amount of fresh air that is provided to a room in a given period of time is known as the ventilation rate, or fresh-air supply rate. What is necessary for adequate general ventilation will depend on factors, such as the amount of floor space per occupant and the work activity.

The HSE says the fresh-air supply rate should not normally fall below 5 to 8 litres per second, per occupant. The Building Regulations states a rate of 10 litres per second, per person in an office setting.

If an area does not have any means of mechanical or natural ventilation, such as windows or vents that can be opened, or if the area feels stuffy, has stale air or smells, then it is likely to have poor ventilation and should be prioritised for remedial action.


Monitoring workplace CO₂

It is possible to use a CO₂ monitor to assess an areas ventilation. Because ventilation dilutes CO₂ exhaled by a room’s occupants, a high CO₂ concentration indicates poor ventilation. According to the Chartered Institute of Building Service Engineers (CIBSE), indoor air at 600 to 800 parts per million (ppm) CO₂ indicates a relatively well-ventilated room. CO₂ concentrations greater than 1,500 ppm are indicative of a very poorly ventilated space. However, in low occupancy or large volume spaces, a low level of CO₂ cannot necessarily be used as an indicator that ventilation is sufficient. The HSE has more information on using CO₂ monitors to identify poor ventilation.

Mitigation measures should be specific to the environment, taking into account the nature of the building and users, the ventilation type and activities that are carried out.

Improving ventilation in a room might be as simple as opening air vents and doors. If the room is ventilated via a mechanical system, maintenance of the system may need to be addressed or the settings changed.

If ventilation is still inadequate, it may be necessary to change how the space is used, for example restricting the length of time people spend in it or reducing the number of people using it at any one time. Ultimately, it may be necessary to install mechanical ventilation in the room.