Corona Corsi-Rosenthal box

But round fans are addressed here with some examples:
https://cleanaircrew.org/boxfanfilterfaq/#collapse_940_26

These are the instructions I followed the most

Standalone HEPAs or Corsi-Rosenthal boxes are quick a way to lower the risk of inhaling SARS-CoV-2 virus. Filtering the virus out of the air reduces the chance of inhaling it---simple logic. The other option is to filter/trap it with a mask before it is released or inhaled

We have them, they just can't be bought at the local department store for €15:

A mega thread on the ultimate DIY air filter known as the Corsi/Rosenthal Box (corsiaq
/ jimrosenthal4
).

Round Fan Build

source

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