Could it be bad for your health to light a fire in an indoor fireplace?

Usually ok: If the flue is open ; working properly. The flue vents exhaust gases to the outside. Chimney also needs to be properly constructed. However, even w this - you will still get some debris /smoke particles in room. We lived in a cabin in the blue ridge mountain (over 250 years old) with a chimney that wasn't properly built. We got smoke in the room no matter how well the fire was made.