When I first heard about electro-magnetic pulses it was within the context of discussing nuclear bombs. My father explained that electronics would fail following exposure to an electro-magmetic burst in the region of the bomb itself. I can remember thinking that with skin melting off people and hair dropping out within days, that my transistor radio failing was at the bottom of my list of things to be concerned about if that ever did happen.
I remember hearing about it again in the nineteen-eighties when I was gathering materials for my own young family's disaster planning, and EMP was not quite so clear, and not quite so easily dismissed. I fashioned an American-made metal trash can with a well fitting lid. I lined the bottom and sides with styrofoam so as not to allow contact with the object and the metal sides. Then, voila ! I had an inexpensive, and most likely effective Faraday cage. I later secured the lid with a little duct tape. In the years which followed I placed a reserve insulin pump in there, a solar radio, a couple of different blood glucose monitors, and a portable pulse oximeter. We were well prepared and our electronics were protected.
In the years since there have been discussions of a number of nations having cultivated and created an electro-pulse weapon designed to disable the enemy's communication and possibly travel devices also. I remember when President Clinton's helicopter crashed killing the crew aboard, rumors of an EMP weapon which was being tested by a Maryland contractor. Would my Faraday cage protect the electronics stored there ?
EMPs are not all the same. The type of energy from which the EMP originates can differ. They can be negative or regular pulse trains. They can be natural or unnatural pulses. They can have varying frequency ranges, and differing pulse waveforms. Thinking of an EMP as one entity is a lot like considering all earthquakes to be the same. Each event can be unique.
There are natural EMP events. One would include a lightning strike. We all know how badly lightning can damage anything electronic, and for that matter, I personally can attest to what damage it can do to human beings and to animals. Another one can be an electrostatic discharge. We've all shocked ourselves walking across a carpet and then touching a doorknob. Such a shock can be dangerous to a patient with an intravenous line or those who are critically ill. Few people realize that a natural electrostatic shock can wipe out the programming of an insulin pump, causing the basal and bolus features to need to be reprogrammed entirely.
Unnatural or man-made EMPs can be caused by, as I mentioned prior, a nuclear bomb. This would normally be a fairly local phenomenon, however a high altitude nuclear detonation, could wipe out all of the electronics for a rather broad area. This application probably has great weapons potential and the abatement of such has likely been the focus of our military. There is also the EMP weapon which is suspected to be within the arsenal of the US, France, England, China, Russia, and probably other nations as well. Other types of low impedence EMP interference can also be man-made. These would include the types of EMP generated inadvertently from other electrical activities. Relays, solenoids, and other devices generate some EMP. Electric motors cause a train of disruption when they run. Power line surges can also generate EMP.
The point is that one EMP is not like another. We cannot completely predict the effect an EMP might have on a particular piece of electronics. There is also a considerable amount of pop culture lore on EMP weaponry which interferes with the public's ability to understand and appropriately shield for it.
The best that most of us can do is create a Faraday cage for essential back up electronic devices. An inexpensive cellular phone might be a good idea to place in there also, despite the fact that the cellular towers could be damaged from an event and be disabled. I know others who have shielded the interior of garages and even basements. I know still others who store essential electronics in non-functional microwave ovens for safekeeping.
Although this is a consideration in preparedness, make sure that you have adequate water, food, tools, medicines, and have anchored heavy objects so that they do not fall on people during an earthquake. Make sure that you have planned FIRST for the disasters which are most likely in your region. We can speculate and anticipate EMPs afterward.
More information on EMP and protective measures: