3. Assessment of fresh air (ventilation) in the workplace
There are several factors to consider when deciding on the ventilation needed in your work areas.
You must make sure there is an adequate supply of fresh air in any workspace. You can do this by using:
- natural ventilation - fresh air comes in through open windows, doors or air vents. This is also known as ‘passive air flow’
- mechanical ventilation - fans and ducts bring in fresh air from outside
There may already be different types of ventilation around your workplace.
It may help to make a list of areas in your workplace and how they are ventilated. Floor or design plans may help with this.
Alternatively, you could walk around the building and make a note of each area and how it is ventilated.
Remember to include changing rooms and areas used for breaks, such as canteens. If you can’t tell easily how an area is ventilated, it may be because it is poorly ventilated.
How many people use or occupy the area?
The more people who use or occupy an area, the greater the risk that an infected person is there, increasing possible exposure to aerosol transmission.
The risk increases if an area is poorly ventilated and occupied by more than one person.
Consider how many people use or occupy an area at any one time. Is there a set number of people each day or do numbers fluctuate?
How large is the area?
The larger the area, the lower the risk. This is because larger areas:
- have more air to help dilute the virus
- tend to be designed with ventilation rates in mind
- take longer for aerosols to build up in them
What tasks or activities take place in the area?
Activities that make you breathe deeper, for example physical exertion or shouting, will increase:
- generation of aerosols
- risk of transmission
Activities like these increase transmission risk even where there’s adequate ventilation.
If possible, avoid or redesign these activities to reduce the risk. This could include moving some activities outside or working alone where possible.
Are there any features in the workplace that affect ventilation?
You may have large machinery, equipment or other features that could prevent air circulating in your premises. These features could include things like pillars or posts.
Large machinery or physical features could make the air stagnant. Consider how to improve airflow in the area.
Do you use desk or ceiling fans?
You should not use desk or ceiling fans in poorly ventilated areas.
Does your workplace use local exhaust ventilation?
You may use local exhaust ventilation (LEV) to control risks from other workplace hazards such as dust or welding fumes. If an LEV system discharges the air outside, it will improve ventilation in the area.
Is there a complex ventilation system?
Workplaces that may have complex ventilation systems include:
- some old buildings
- buildings with multiple floors and rooms using different ventilation systems
- systems designed for product manufacturing as these can include additional recirculation
If your workplace has a complex ventilation system, there is guidance from the Chartered Institution of Building Services Engineers (CIBSE).
You may need a ventilation engineer to provide expert advice on the best system for your workplace.
How will you tell your employees about the outcome of your assessment?
You should tell your workers about the outcome of the risk assessment.
This will help them understand how they can play their part to reduce the risk of spreading COVID-19.
Find out more
The British Occupational Hygiene Society has worked in collaboration with the Health and Safety Executive to develop a freely available tool for assessing general ventilation and COVID-19 transmission.
The tool supports employers, building users and building owners by using a simple scoring system to indicate the effect their ventilation arrangements are likely to have on reducing COVID-19 transmission. It also provides recommendations for taking action, where appropriate.
We review and update this page regularly to reflect any changes in guidance.
Page last reviewed: 06 October 2021
Next review due: 31 October 2021