This is a curious thing- on the NPS beaches in the Cape Hatteras Nat'l Seashore fires must be BELOW the high tide line, I guess so that the rising tide would kill any remaining embers.
But, with the erosion in some spots being what it is, during a king tide the high tide line/strong NE wind will sometimes put that line AT the dune line. Any of you that have dealt with a beach grass fire know how well and quickly the oils in the grass burn/spread.
Just be smart. Stop and Think.