I have a room where I exposed a brick wall and redid the mortar by tuckpointing. It look beautiful but the whitish residue from the mortar needs to be cleaned and the best way to do it is using hydrochloric (AKA muriatic) acid. I have done that before and the results are beyond amazing. It made my 100+ yr old brick look brand new clean but with the old retro shape. One couldn't ask for more.
However, in this room, another thing that is partially exposed are spiral AC ducts, although on the other side of the room from the wall. I was concerned whether the vapors from the acid may corrode the metal ducts and whether it makes sense to wrap it in some sort of plastic sheeting.
I do plan to use a gas mask and goggles with the window open and a fan blowing out hard when I'm doing this. I know it's not recommended for indoor use but the results I got before were so awesome that I don't wanna settle for anything less.