Clean air

This is not complicated - we get infected with Covid by breathing in polluted air, the solution is to clean the air we breathe.

Air cleaning is discussed in terms of equivalent air changes per hour, eg, an air purifier rated at 4ACH (for a room of x size) means using that filter is the same as if the air in the room was completely replaced with outside air 4 times each hour.

Air quality can easily be measured using a CO2 monitor - note this is a proxy it doesn’t actually measure contaminants in the air - we breathe out CO2 so high CO2 indicates you are breathing in air that someone else has breathed out. The only problem is that using an air filter removes pathogens but not CO2, so the CO2 measure gives a false reading in this scenario, but given right now there is no air filtering anywhere CO2 is a really good way to see what the fresh air level is like.

The most effective action we can take is to have good ventilation, open windows causing a good through flow. This is challenging in winter.

Hepa filters (Hepa is just a standard that says how small the particulates are that it filters) remove Covid from the air and are relatively inexpensive, they can equally be used at home and in workplaces. The power of a filter is given based on how many effective air changes it achieves in a specified room size.

Two incredible engineers came up with a design for a DIY air filter, known now by their names, Corsi-Rosenthal See this site for an example of how to build. Some schools have run projects where students help build Corsi-Rosenthal boxes, usually referred to now as CR Boxes, and they then run them in each class.

Studies have shown that running Hepa filters in schools leads directly to reduced levels of infection and sickness absence.

With a handful of exceptions (whose Heads are heroes) schools in the UK are refusing to implement Hepa filters, even, staggeringly, where parent groups have crowd funded them and offered them to the school for free. Head teachers have hidden behind ‘government guidance’ statements, so post Covid Inquiry it will be interesting to see if schools start to realise this isn’t going to be a valid defence.

Clearly every indoor space should be running Hepa filters as a minimum, that even schools and healthcare settings are not doing this is criminal.

The longer term solution is probably UV light. Germicidal UV was actually widely installed in the 1960s to combat measles, but as measles disappeared so too this gradually disappeared. That generation of UV operated across the top of a room as direct contact with skin or eyes is dangerous. A newer technology called Far UV (just a specific frequency range, 222 nm) allows UV light to completely bathe a room, neutralising exhaled pathogens in seconds.