Can you see the name of the manufacture of the brick on any of the bricks?
How old is the fireplace?
It looks like it has been used and does not show signs of deterioration so I would say it is firesafe.
Unless they did not know what they were doing it is hard to believe someone put that much time and energy into building something that was not firesafe.
Invasive plants are Earth's way of insisting we notice her medicines. Stephen Herrod Buhner
Everyone learns what works by learning what doesn't work. Stephen Herrod Buhner
Without a closer picture, it is impossible to say if those are Fire Bricks or not.
All clay bricks are Fire Safe; a red concrete brick, however, would not last in a hot environment.
Offhand, I would expect that those are red clay bricks, good to 800F
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