 (This is a Kearny air pump, or KAP, named after the inventor, Cresson Kearny)

Unfiltered air is safe, since the most dangerous fallout has the consistency of sand or finely ground pumice.Such large particles are not easily ingested into the soft tissues of the body, so extensive filters are not required.Any exposure to fine dust is far less hazardous than exposure to the fallout outside the shelter.