Depends on the wall. Solid concrete, safe. Residential interior wall made of plaster, not safe. Brick wall, safe. Near a window, not 100% safe. Do you know the composition of a wall? Chances are no, so remove ass from the area.
They have an injury radius of about 50m, so 100m of free air is safe.
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.