Last reviewed 20 April 2021

The HSE has issued updated guidance on how to use ventilation as a control measure to reduce the risk of aerosol transmission of Covid-19 in enclosed spaces. 

The guidance states that risk of transmission is greater in spaces that are poorly ventilated.

Poorly ventilated areas may be identified by:

  • looking for areas where people work and where there is no mechanical ventilation or natural ventilation such as open windows, doors or vents

  • checking that mechanical systems provide outdoor air, temperature control or both. If a system only recirculates air and has no outdoor air supply, the area is likely to be poorly ventilated

  • areas that feel stuffy or smell bad

  • using carbon dioxide (CO2) monitors (monitors are less effective in areas used by few people).

According to the guidance there are different ways of providing ventilation, including mechanical ventilation using fans and ducts, natural ventilation which relies on passive flow through openings (doors, windows, vents) or a combination of the two. Note that ventilation will not reduce the risk of droplet or surface transmission, so other control measures such as cleaning and social distancing are also required.

Before restarting operations, mechanical ventilation systems (including air conditioning systems) may need to be serviced or adjusted so they do not automatically reduce ventilation levels as a result of lower than normal occupancy levels. Positive pressure systems and extractors can operate as normal.

Mechanical ventilation brings fresh air from outside into a building and should be maintained in line with manufacturers’ instructions. They will provide adequate ventilation if they are set to maximise fresh air and minimise recirculation.

Where it is not possible to provide adequate ventilation through the measures above, it is possible to use local air cleaning and filtration units, such as high-efficiency filters or ultraviolet-based devices, to reduce airborne transmission of aerosols.

Carbon dioxide detectors are not suitable for use in areas that rely on air cleaning units to provide ventilation.

The Government has updated its Covid-19 secure guidance to reflect this.

Meanwhile, the Trades Union Congress is urging businesses not to drop their guard on workplace safety. If workplaces are not Covid-secure, coronavirus cases could spiral out of control again.