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Can CO2 help with indoor COVID transmissions?

There are 3 types of COVID transmissions: Fomites (wash hands, surface cleaning), Droplets/Close-Contact Transmission (social distancing, hand washing) and Long-Range Transmission (ventilation).

Ventilation is the new buzzword and is the current strategy for controlling the spread of COVID-19 indoors. As more businesses open their indoor spaces and control of crowds are removed, it is important we understand the role ventilation and fresh air plays.

There will be a greater risk of viral transmissions when individuals are in the same room/space together for an extended period of time with low ventilation rates.

So how can we be sure we are safe?

CO2 monitoring can be a cost-effective way to identify spaces with high occupancy and/or poor ventilation, and for actively managing ventilation in a space. Professor Catherine Noakes, who specialises in airborne infections, warns that ‘the numbers are not exact and don’t tell you actual risk from the virus, but they are useful in helping you to improve general ventilation’.

If your room measures CO2 levels of 800ppm (parts per million), then your ventilation is probably good. However, if CO2 levels regularly rise above 1500ppm then you need to open the windows/doors to release the stale air and let in fresh air.

And what steps can we take?

We believe all homes and businesses should have an air quality monitor as it is essential to know the air you breathe.

  • In the workplace The law says employers must make sure there’s an adequate supply of fresh air (ventilation) in enclosed areas of a workplace. This has not changed during the pandemic. Your facilities manager should be able to tell you the ventilation strategy and if they are monitoring CO2 levels (see further reading below). Bringing in your own plug-in or portable Air Quality Monitor can give you peace of mind that you are working in a safe environment.

  • Shops, clinics, gyms, hospitality If doors and windows are closed and you can’t see an air purifier, don’t be afraid to ask businesses about their HVAC ventilation system and what steps they are taking to keep you safe. HVAC systems are either fresh air or recirculating with the latter not advised as it can recirculate viruses from one room to another. The fresh air system should ideally have their filters upgraded to HEPA to filter out viruses and these HEPA filters must be replaced regularly.

  • At home Keep doors and windows open when you have visitors and have your eye on the CO2 monitor. If you are unable to open the windows, run your HEPA air purifier on high and keep it on high until about 20 mins after your visitors leave.

  • Balancing ventilation with thermal comfort and outdoor pollution Fresh air ventilation is the best strategy to dilute stale indoor air by replacing it with fresh air. We researched the efficiency of our purifiers and it found that it still works with windows open, but the efficiency reduces from 95% to 60%. This is great to know if you live in a highly polluted area as the fresh air will reduce the CO2 and the HEPA purifier will filter out the particle pollution (a Carbon filter will capture fumes).

What type of Air Quality Monitor do I need?

The best monitors use the more reliable NDIR sensors for CO2. For a quick visual reading on levels, monitors with red/amber/green lights are useful. For a more accurate reading, place the monitor away from windows and doors to avoid false positives. Monitor your CO2 levels, especially when you have visitors at home or if there are groups of people congregating for some time.

A good monitor should give you access to real-time data. This data lets you look at averages and patterns in CO2 levels. You should expect that within 20-30 minutes of people entering a room, the levels will rise and then settle on a steady number. But if they continue to rise consistently over 40 minutes to high levels, the room is poorly ventilated and increases the chance of viral transmissions. High CO2 levels can also affect concentration, more about this in another blog.

The bottom line: If CO2 levels are high, open the windows or doors and let in fresh air. You can also turn on your air purifier, which won’t reduce CO2 levels, but the HEPA filter will capture viruses and other particles in the air.

Further reading:

Our products:

  • Our award-winning HEPA purifier will trap particles smaller than the size of a virus

  • Our CO2 Monitor has an industrial-grade NDIR CO2 sensor


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