The way that shelf is mounted, it looks like it is part of the building thus 314.29 may be violated.
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314.29 Boxes, Conduit Bodies, and Handhole Enclosures to
Be Accessible. Boxes, conduit bodies, and handhole enclosures
shall be installed so that the wiring contained in them can
be rendered accessible without removing any part of the build‐
ing or structure or, in underground circuits, without excavating
sidewalks, paving, earth, or other substance that is to be used to
establish the finished grade.
I wouldn't put it past some people to still try and jam a plug in there! Be real interesting when the prongs scrape the paint off that metal bar!
Remove the shelf, put a baby safety plug in, remount the shelf.
Problem solved.
IMO a safe is not part of the building, the shelving is.
I don't see how a shelf that can be readily removed is "part" of the building, but I suppose that could be argued. What if you put a 500 pound safe in front of it? Would that be a violation? It would be far less accessible than this situation.