During which events is it most likely that sheltering in place is the best option?

Nuclear attack (tornado, tsunami)

Explanation:

Well, at those attacks, when being on surface can be dangerous. So, any kind of disturbed oxygen (eg with some gas attack). Also when there is an air strike for example.

Shootings, tornados and radiological or chemical disasters

Explanation:

To shelter in place is to find a safe location indoors and staying there until you are told to evacuate by authorities. This kind of shelter is used when there's a shooting, a tornado, radiological or chemical hazards, or another situation that requires you to be locked down until danger is gone.

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