Can't find anything specifically on Type I, but this wikipedia article touches on it briefly. It says a Type II within 8 parsecs would kill off 1/2 the life on the planet. read more
There is geological evidence of a supernova about 2.5 million years ago. That's estimated at a distance of only about 150 light years. So, I would say that "about 150 light years" is possibly the best answer for KNOWN close supernovae. read more
Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. read more