About 20 years ago I started working for an IT service provider in Leeds. Not long after I started with them, they moved in to a new building up the road which was directly under a 475KV power line (the really big ones). We moved all our kit in, and discovered that our CRT monitors were completely unusable due to the magnetic field from the power cables scrambling the displays. There was revolt from all the staff of course since we didn't fancy sitting in such a strong magnetic field. Some people suggested a Faraday cage in the roof void might help, but in the end management simply replaced all the CRT monitors with LCD and declared the problem fixed
I left after a couple of months.