Spray Foam and Mini Lights Safety

I have decided this year to make a pile of burning embers to place in front of a tombstone for my outdoor Halloween display. I made it with regular orange "christmas" style mini lights (non-LED). I basically laid down a thick trashbag, spread out the lights, and covered them with cans of Great Stuff Spray Foam. Is there any cause for concern of fire hazard running this display on my front lawn for 4-6 hours each night? Also, is there anything to do to prevent the black spray paint from just wiping off the totally cured foam (I waited over 24hours to paint it)? Thanks!