2. Assessing the risk of poor ventilation

As part of your legal duty to provide sufficient fresh air, your workplace risk assessment should identify poorly ventilated work areas:

  • look for areas where there is no natural ventilation (open windows, doors, or vents) or mechanical ventilation (fans or ducts bringing air in from outside)
  • identify areas that feel stuffy or smell bad
  • consider using a CO2 monitor to identify poor ventilation

It may help to list areas in your workplace or use floor plans to record how areas are ventilated. Remember to include changing rooms and areas used for breaks, such as canteens.

Understanding when to take action

The ventilation rate

The ventilation rate refers to the volume of air that is provided to a room over a period of time. What is necessary for adequate general ventilation will depend on several factors such as the amount of floor space per occupant, and the work activity.

HSE's Approved Code of Practice and guidance states that 'The fresh-air supply rate should not normally fall below 5 to 8 litres per second, per occupant.' A value of 10 litres per second per person is recommended in some building guides as a suitable value for most commercial buildings.

In some workplaces, like draughty workshops, it is obvious there is enough air. In other, more enclosed settings, it can be difficult to estimate the flow rate of air in a space, particularly for natural ventilation, but a useful way to do it when you think you may have a problem is by using CO2 monitors.

Complex ventilation systems

If your workplace has/requires a complex ventilation system, for example due to having multiple floors, more detailed guidance is available 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.

Desk or ceiling fans

You should not rely purely on desk or ceiling fans in poorly ventilated areas. They won't improve fresh air.

Local exhaust ventilation

You may use local exhaust ventilation (LEV) to control risks from workplace hazards such as dust or welding fumes. If an LEV system discharges the air outside, it will also improve general ventilation in the area.

Talk with your workers

Talking with your workers will help you assess the risk and put in effective measures to improve ventilation.

Questions to ask them

  • How do we bring fresh air (ventilation) into our workplace?
    • Think about natural ventilation through windows, doors and vents you can open fully or partially
    • If we use mechanical ventilation, is it set correctly and do we maintain it?
  • How can we improve ventilation?
    • Think about areas that feel stuffy or smell bad – open windows, air vents and doors (not fire doors)
    • If we have recirculating systems, do we bring in some fresh air?
    • Are temperatures in the workplace comfortable?

Discussing the outcome of your risk assessment and the measures identified will also help them understand how they can play their part in improving ventilation at work.

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