I have a very big workshop/Garage and it is 95% metal. Would it protect my cars electrical systems in the event of an EMP attack?
An enclosed metal structure is ideal for protection of electronic systems against an EMP attack (or a natural EMP occurrence from the sun). There is one very large caveat though… that is, there can be no big ‘leaks’ in the structure. A 95% enclosure will still allow electro-magnetic radiation to get in, provided that the opening is larger than the wavelength of the radiation.
An ideal Faraday cage is enclosed in metal conductive material on ALL (6) sides, including the floor. This could be the Achilles heel to stand-alone metal sheds that are simply setting on the ground with no conductive material underneath to complete the enclosure circuit. EM radiation, if strong enough, will be conducting through the top surfaces of the ground and may find its way in through the open floor. A well constructed and grounded floor ‘may’ suffice though – poured concrete with re-bar that is well grounded for example.
An important factor to keep in mind is to be sure that the ‘electronic’ items that you are protecting should not be in contact with the metal enclosure of the Faraday cage. Keep them electrically insulated from it in some way – including from the floor.
To keep out microwave frequencies (emitted during an EMP along with other broadband ‘noise’), a typical screen mesh is small enough to keep it out, given that microwave wavelengths are about 5 inches, and provided that the seams of the screen-to-metal are electrically connected with the metal framework.
Also of note, a vehicle’s electronic systems are located all over the place on the vehicle. Although many parts of the vehicle are enclosed to a large degree, a problem is that most cars today have a-lot of plastic instead of metal on their enclosures, and would not prevent all EMP from getting in.
Your best solution sounds like plugging up the 5% leakage that you have with some sort of metal conductive screening material. Your doors must also be metal or entirely screened. The diameter holes in chicken wire should ‘technically’ be sufficient, but I would be safe and go with metal window screen mesh.