Skip to content Skip to navigation menu


Working safely during Coronavirus (COVID-19)

The HSE has updated its advice on keeping workplaces safe during the pandemic by identifying poorly ventilated areas using CO2 monitors. This ventilation update and expert advice has been written in line with The World Health Organisation (WHO) and government recommendations and guidelines.

Why Ventilation is Important

When people breathe out, small particles (aerosols) and droplets are released in exhaled breathe. If that person carries a virus, they will transmit aerosols of the virus into the air which can build up. This is most likely to happen in enclosed spaces that have poor ventilation and from activities that require people to breathe out more small particles, for example singing, loud talking or high intensity exercise1.

Residual virus can remain in the air after an infected person has left the room and therefore increase the risk of COVID-19 spreading. Adequate ventilation can reduce how much virus is in the air and help reduce the risk of aerosol transmission from breathing in the virus.

Ventilation Explained

Ventilation is the flow of air through a space. Letting fresh air in circulates the particles within an enclosed space and removes the indoor air.

HSE states that good ventilation is one of the best ways to fight COVID-19 in the workplace1.

Watch their educational video on how ventilation can be used to help reduce the risk of COVID-19 transmission.

There are two main ways of increasing ventilation into a space. Natural ventilation, from opening doors and windows and controlled (mechanical) ventilation in the form of systems such as powered fans.

Natural Ventilation

Natural Ventilation relies on letting in fresh outdoor air into indoor spaces and removes indoor air without the use of any fans. When opening doors, be aware not to prop open any fire doors.

If there are a lack of openings, ventilation will be less effective in that area and mechanical ventilation may be required.


  • It's an instant source of ventilation
  • It's free
  • Fresh air has mental and health benefits


  • Can be unpleasant if cold or wet weather conditions
  • Not all spaces have windows or air vents to open
  • Opening doors or windows can cause other nuisances such as noise or smell
Natural ventilation by window

Mechanical Ventilation

Mechanical ventilation moves air in and out of a space using fans or systems. Ensure settings are enabled to maximise fresh air and minimise air recirculation as this can increase the risk of transmission. Recirculating air does not draw in a supply of fresh air and will only move air around, which could include COVID-19 particles if someone infected has been in that area.


  • Alternative solution if natural fresh air is limited or not available
  • Provides more consistent ventilation
  • Can be more effectively controlled, depending on the size of the space or number of occupants within a space


  • Air conditioning and other recirculation units can mask poor ventilation
  • Includes installation, running, maintenance and servicing costs
  • Can become a complex system depending on the size of the room or building
Mechanical ventilation

Identifying and Managing Poorly Ventilated Spaces

To mitigate the risk, ventilation should be considered within your risk assessment by identifying poorly ventilated spaces that are usually occupied.

  1. Look for areas where people are present for an extended time with no mechanical or natural ventilation
  2. Identify higher risk areas where you may need to improve air flow
  3. Prioritise the improvement of poorly ventilated areas

Carbon Dioxide (CO2) Monitors

Measuring ventilation within a space can be difficult to accurately measure ventilation, but in some spaces, it is possible to use carbon dioxide (CO2) monitors to estimate the effectiveness of the ventilation.

As well as aerosols, people also exhale carbon dioxide when they breathe out. Although CO2 levels are not a direct measure of possible exposure to COVID-19, checking carbon dioxide levels can help you measure a build-up within an enclosed space. By identify poorly ventilated areas, measures can then be put in place to improve ventilation and reduce the risk of transmission.

CO2 Monitor

How to Use Carbon Dioxide (CO2) Monitors

  • When positioning CO2 monitors indoors make sure they're positioned at head height, away from people, and kept away from air supply openings such as windows and doors
  • For the most reliable readings, take measurements for CO2 when the space is occupied, with the number of people who would usually occupy that space, for at least an hour

Using CO2 Measurements

CO2 measurements should be used as a broad guide to ventilation within a space rather than treating them as safe thresholds. The amount of CO2 in the air is measured in parts per million (ppm).

  • CO2 values consistently below 800ppm, is likely to indicate that an indoor space is well ventilated
  • CO2 concentration constantly exceeding 1500ppm indicates that a room is likely to be poorly ventilated and may pose a greater risk for COVID-19
  • CO2 readings consistently higher than 150ppm, indicate that action needs to be taken to improve ventilation in this area

CO2 monitors can be used to identify spaces where ventilation is poor, but less effective at showing good ventilation.

What Can You Do in Addition to Ventilation?

Although ventilation is important it doesn't reduce droplet transmission, from people being in close contact or contact transmission, from touching infected surfaces.

You should also make sure you’re working safely by:

  • Keeping your workplace clean
  • Socially distancing by 2m where possible
  • Ensuring workers are frequently washing their hands and wiping down surfaces
  • Identifying other control measures through a risk assessment
  • Talking to your workers and:
    • Letting them know why ventilation is important
    • Ensure they're aware of any measures put in place
    • Explain how they can play their part in reducing the spread of COVID-19

More from Arco

All Expert Advice