Good morning, following on from a visit by the Health and Safety Authority to our hospital, I was requested to carry out an indoor air quality risk assessment on the basis of the document ‘Code of Practice for Indoor Air Quality’ (HSA, 2023). On the day, the inspector was very keen on the use of CO2 monitors and mentioned a direct link between raised CO2 readings and Covid-19 outbreaks. I’ve done some research since but couldn’t find enough evidence to support this claim. Is the use of CO2 monitors something that is recommended in healthcare facilities? Also, the use of HEPA filters was mentioned but again, it’s very hard to find guidance on their use (e.g. in which settings or situations) based on evidence. I have done the risk assessment as requested, but am still unsure on how to proceed with these two items. Our hospital is a small community type hospital, an older building with only windows for ventilation. As our biggest risk I would see the two 12-bedded nightingale wards. I would be very grateful for your advice on this!