An electromagnetic pulse or EMP may be harmless to humans, but its effects on society may well be crippling. It carries energy that’s similar in magnitude to conventional radio waves, but EMP is sent in a “burst” – imagine receiving sunlight packed in less than a second. Some EMPs also fire in several pulses, which can deal additional damage. As a result, a sufficiently strong EMP attack can shut down power grids and telecommunication equipment, even the internet, whose data farms require lots of power. It can also incapacitate refrigeration, water services, security systems, banking systems, and transportation.
Recovery from an EMP attack is possible, but it may depend on the area and how widespread it is. An EMP attack that affects an entire country, however, may take years, even decades to recover. Such an incident leads to a collapse of law and order, which preppers should plan for when building a BOB (bug-out bag) or a Faraday cage.
For starters, you want to shield any equipment that will let you communicate with other people or help you survive in a world that’s suddenly without power. These things include:
A Faraday cage, in essence, is an enclosure lined with sheets of aluminum foil or a box with aluminum wire mesh. Aluminum is shown to block electromagnetic fields. You can use custom-made boxes or make your own using an ammunition can, steel barrels, or even a garbage can. Faraday cages don't need to be grounded.
Your microwave oven can also act as a Faraday cage in a pinch. This device not only keeps radiation in, but also keeps it out. Anti-static bags are also an additional layer of protection that you can use in which to store your electronics.
How effective your Faraday cage is depends on the intensity of the EMP, its distance from the source, and the radiation emitted by the EMP. Naturally, the closer you are from the source, the more protection the contents of the Faraday cage requires. Some rays, however, like gamma and X-rays, can penetrate through layers of solid material and will require additional metal sheeting for protection. (Related: Here's a comprehensive guide on how to prepare for an EMP attack.)
EMP attacks strike with little to no warning, and you may have no time to stash your belongings into your safety box. The best way to prepare for an attack is to store spares into your Faraday cage so when SHTF, you have working equipment ready to go.