"A nuclear explosion may occur with or without a few minutes warning," reads the page, which was updated on Friday. "Fallout is most dangerous in the first few hours after the detonation when it is giving off the highest levels of radiation. It takes time for fallout to arrive back to ground level, often more than 15 minutes for areas outside of the immediate blast damage zones.
FEMA recommends the following steps to prevent 'significant radiation exposure,' which include "Try to maintain a distance of at least six feet between yourself and people who are not part of your household," and "If possible, wear a mask if you're sheltering with people who are not part of your household."
https://invesbrain.com/fema-in-case-of- ... ar-a-mask/
