what is the purpose of this fireplace accessory?

[Michael Thomas]

1) What is it called?

2) What was intended to do?

3) Is it possible that acting as a jack-screw it created at least some of the gap seen in the second picture?

[Vern Heiler]

Looks like it is for a crane?

[David Bell]

Looks like it may have held some kind of rack over the fire whether for cooking or smoking of food.

[H.G. Watson, Sr.]

DB's right. That's a height adjustable swing arm for holding kettle, dutch oven, steam kettle, iron plate, etc.

Not quite sure what you're referring to in the second picture. Exposed unparged refractory or support material (lintel) and a hinge plate same side as the cooking accessory (deeper) or opposite or is this with the pot stand removed looking up? (assuming so).

Shouldn't have but could have since no plate and if over extended and over heated could but more likely you'd see breaking up at the base.

Usually such a gap is at least partially due to settlement (building shifting or fireplace foundation/footing).

Looks like a DIY conversion, removal of some elements and reface - lacking in safety details modifying original fireplace. Not really pictured but don't see much of a hearth there either. Poor maintenance prior possibly some settling/shifting and some overly hot/large uncontained fires after what was removed (or failed for minor fire, damper fell closed mid-fire, or wasn't opened) and not replaced or corrected with the not so properly applied refinish surround. I'm assuming a lot and possibily coming to wrong conclusions based upon what I think I'm seeing. I'm assuming before the applied tile/stone when brick was showing there was either a track and fire curtain/chain or doors which has since been removed, and the grate/fire has been moved forward and it is being used open without doors or containment. Also appears at one time they had a piece of this refinish material applied to the front/lintel and it is now gone (think I'm seeing void "slot" in the tile/stone to the left of the opening).

Log grate too deep or forward - what's BH's signature line - keeping fire IN the fireplace?

However, as you know, it is obvious a Level II at minimum is required on site.

Call for a Level II, possibly Level III will be warranted. Creosote/soot/etc. may have infiltrated the gap between the fireplace & chimney and the wall.

[Bo Tasso]

In the second photo, is that possibly a combustible material? That would be a major issue.

[Bob Harper]

I agree on the pot crane in pic #1. The second photo appears to be a profile gap, which can create a "second chimney effect". This means heat, smoke and creosote can migrate up behind the decorative profile all the way up to the ceiling where it can ignite combustibles. For this reason, it is now addressed in NFPA 211 to be sealed.
The front lintel should be at least 8" below the damper frame.

I have removed charred newspaper from these gaps so it is not uncommon to find combustibles there as Bo discussed.