I have a bunch of reclaimed (broken) bricks left over from building a patio. The bricks are from an old home that was knocked over and buried for some time. I would like to use these to build a fire pit on the patio, but I've read there can be some safety concerns using bricks/blocks that aren't "fire safe".
My question is, how concerned should I be about using these old bricks? It seems unlikely that they'd blow up to me but I like to keep things as safe as possible.
Are there are any other things I should be concerned about such as mortar type? Base? etc?
Here are the bricks (red ones):