The biggest solar flare known occurred in 1859: http://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare/ http://science.nasa.gov/science

The biggest solar flare known occurred in 1859: http://science.nasa.gov/science-news/science-at-nasa/2008/06may_carringtonflare/ http://science.nasa.gov/science-news/science-at-nasa/2008/06... probably a 500 year event. It set telegraph paper on fire and would have fried any exposed electronic equipment. however anything in a Faraday cage or underground should survive.