[Petrochemicals (OP)]

Not mentioning corona here, but the subject has fostered discussion in Germany about ventilation. They are now investing in new ventilation to the tune of  500M Euros for things like co2 sensors and humidity.

https://www.bbc.co.uk/news/world-europe-54599593

Current building regulations in the UK mandate a  certain change rate per hour for the building use and occupancy, but is this really healthy, considering outdoor spaces are considered safe for virus transmission? If buses had open sides how much would this affect the jeopardy of passengers to health issues.

Is humidity safe at 22 degrees C?

Is the airflow pattern considered?

Is co2 an issue?

[evan_au]

The drive for energy efficiency (and cost efficiency) means that air is often recirculated within a building, rather than being replaced by fresh air. This means that pathogens and CO₂ builds up over time.

Installing a UV sterilizer in the air path will help kill pathogens, but the CO₂ levels will indicate that the air is not being replaced regularly.

An alternative is to use a heat exchanger so that you recover (some of) the heating/cooling energy that was expended by the air conditioner.

[alancalverd]

Fresh air CO2 level is less than 0.05%. 0.5% is found in some classrooms and is observably detrimental to performance, demanding remedial action in manned spacecraft. 5% is toxic. 

Exhaled air is about 4% CO2 which , oddly enough,is the reason mouth-to-mouth resuscitation is effective and anesthetic machines recirculate exhalate: increased CO2  triggers the breathing response very quickly. You breathe about 11 cubic meters per day, so in a sealed box of 1 cubic meter you would panic in 30 minutes (early hyperventilation response to CO2 toxicity), become unconscious in an hour and reach a toxic level in around 2 hours.

100% relative humidity is no problem below 35 degC  but becomes very unpleasant if sustained at much higher temperatures in still air because you can't lose body heat by evaporation. But zero RH quickly dries out the lung surfaces and is just as unpleasant.