Well, depending - I knew someone who's house was pretty much in the middle of a field of shale, excpet for 1 or 2 trees on one side (when I say a FIELD of shale - he ad over 100 yds of bare shale on 3 sides. Of course, he laso had a mid sized Cat dozer, so if I was there, the trees would be gone, I'd dig a DEEP shelter, and work on extending that 100 yd buffer to somethen a tad more. The dozer in the garage came from the fact he used to own a heavy equipment company, and the HUGE empty area was where he used to park a few cranes and the like