Ventilation and Air Conditioning During the Coronavirus (COVID-19) Pandemic

Original Article By: HSE - 19th July 2021

Identifying poorly ventilated areas and using CO2 monitors

The priority for your risk assessment is to identify areas of your workplace that are usually occupied, and poorly ventilated. You should prioritise these areas for improvement to reduce the risk of aerosol transmission.

There are some simple ways to identify poorly ventilated areas:

• Look for areas where people work and where there is no mechanical ventilation or natural ventilation such as open windows, doors, or vents
• Check 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 
• Identify areas that feel stuffy or smell bad 

 

Using carbon dioxide (CO2) monitors

People exhale carbon dioxide (CO2) when they breathe out. If there is a build-up of CO2 in an area it can indicate that ventilation needs improving.

Although CO2 levels are not a direct measure of possible exposure to COVID-19, checking levels using a monitor can help you identify poorly ventilated areas.

Types of CO2 monitor to use

There are many different types of CO2 monitors available. The most appropriate portable devices to use in the workplace are non-dispersive infrared (NDIR) CO2 monitors.

How to use a CO2 monitor

CO2 levels vary within an indoor space. It’s best to place CO2 monitors at head height and away from windows, doors, or air supply openings.

Monitors should also be positioned at least 50cm away from people as their exhaled breath contains CO2. If your monitors are too close they may give a misleadingly high reading.

Measurements within a space can vary during the day due to changes in numbers of occupants, activities, or ventilation rates. Doors and windows being open or closed can also have an effect.

The amount of CO2 in the air is measured in parts per million (ppm). If your measurements in an occupied space seem very low (far below 400ppm) or very high (over 1500ppm), it’s possible your monitor is in the wrong location and you should move it to another location in the space to get a more accurate reading.

Instantaneous or ‘snapshot’ CO2 readings can be misleading, so you should take several measurements throughout the day frequently enough to represent changes in use of the room or space. Then calculate an average value for the occupied period.

You may need to repeat monitoring at different times of the year as outdoor temperatures change and this will affect worker behaviour relating to opening windows and doors when your space relies on natural ventilation.

Your readings will help you decide if a space is adequately ventilated.

How to get the most accurate readings

• Check your monitor is calibrated before making CO2 measurements. Follow the manufacturer’s instructions, including the appropriate warm-up time for the device to stabilise
• Know how to use your portable monitor correctly, including the time needed to provide a reading
• Take multiple measurements in occupied areas to identify a suitable sampling location to give a representative measurement for the space. In larger spaces it is likely that more than one sampling location will be required
• Take measurements at key times throughout the working day and for a minimum of one full working day to ensure your readings represent normal use and occupancy
• Record CO2 readings, number of occupants, the type of ventilation you’re using at the time and the date. These numbers will help you use the CO2 records to decide if an area is poorly ventilated

 

How the measurements can help you take action

CO2 measurements should be used as a broad guide to ventilation within a space rather than treating them as ’safe thresholds’.

Outdoor levels are around 400ppm and indoors a consistent CO2 value less than 800ppm is likely to indicate that a space is well ventilated.

An average of 1500ppm CO2 concentration over the occupied period in a space is an indicator of poor ventilation. You should take action to improve ventilation where CO2 readings are consistently higher than 1500ppm.

However, where there is continuous talking or singing, or high levels of physical activity (such as dancing, playing sport or exercising), providing ventilation sufficient to keep CO2 levels below 800ppm is recommended.

 

For the full HSE report please follow the link below:

Ventilation and Air Conditioning During the Coronavirus (COVID-19) Pandemic