If we stand in an elevator or other metal containers we lose radio signals etc the very same reason for which we cannot see across a block of metal that light cannot penetrate it. However x-rays and gamma rays can.
Now if you see the working of Faraday's cages then from weak to very strong no electric field passes through them which is why they are safe!
Now I would draw the simple conclusion that atleast one part of EM radiation must not be penetrating any metal surface and since EM radiations cannot survive solely as E or M radiation any sort of radiation penetrating metal surface must not be possible.
But in fact x-rays do pass metal surfaces. How can this happen when clearly atleast electric field part of radiation must not penetrate the block?