Put your USB Key in a condom and don't badger staff with wise guy questions. BTW… you do deserve a dirty look in asking such a question. The general service for safe deposit is to store and safeguard assets as opposed to keeping in your house. read more
The bank boxes will likely significantly dampen the EMP with all the metal of surrounding boxes and perhaps underground location. You could potentially build your own Faraday cage that will fit inside a safe deposit box and hold your smaller, precious electronic assets. read more