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:

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.

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.

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.

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

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.

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

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.