A lot of schools have exterior walls that are concrete filled in the US, especially true in tornado and hurricane areas. Interior, I think they went to concrete filled for most of them but you would have to check building codes when the structure was made.
A hollow core cinder block wall should be adequate protection from a grenade.
In the case of a school, painted cinder block walls usually (in the US; why yes, our schools do resemble prisons)
A lot of schools have exterior walls that are concrete filled in the US, especially true in tornado and hurricane areas. Interior, I think they went to concrete filled for most of them but you would have to check building codes when the structure was made.
A hollow core cinder block wall should be adequate protection from a grenade.
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