" fire residue and superheated sand can severely burn bare feet -- use a barbecue that is elevated off the sand"
And the coals stay lit for a very long time too!
I dug a firepit in beach sand and lit a bag of charcoal around 11pm one night and cooked some steaks. Before going to bed I covered up the pit with sand. At 6:00pm the next day I dug out the pit to light a new fire and found live coals from the previous night's bag of charcoal.
Amazing.