I am reposting one of our videos from last year because it warns homeowners exactly of this fire hazard:
Greenwich Patch 2/3/15: ” ‘There was a small section of grout missing on the slate apron. The ember fell into the opening and started to burn the sub flooring’ Kick said. Firefighters pulled up the slate and were able to douse the smoldering wood, Kick said.”
“Fireplace” by Luis Tamayo is licensed under CC BY 2.0