Rotten wood is just harder to light than traditional firewood. Yes it’s safe to burn rotten wood in an indoor fireplace. I recommend using regular firewood to start the fire or at the very least you’ll need to use some type of fire starter(that might not even work).
A howl in the woods
Grant wood stone city
I got loaded wood brothers
Free photo Rotten wood Abstract, Burned, Fibers Free Download Jooinn