Muriatic acid vapors are absolutely NOT safe to breathe. If you even mildly inhale them you will be completely incapacitated for a minute, we're talking absolutely uncontrollable coughing and hacking until you get to some fresh air. You can literally pour the stuff on your hands but it violently attacks sensitive organic materials like your mucus membranes and lungs. (and tools... the vapors that come off the acid will precipitate down in the surrounding area and will etch the finish off your chrome vanadium tools and cause them to rust, seriously).
I would still recommend muriatic acid, it corrodes zinc coating in like under a minute. It gets into the crevices that blasting can't (creck if the blasting missed anything). You don't need anything fancy, just apply several times with a spray bottle over the course of 10 minutes until it stops reacting then thoroughly rinse it off (wash with dish soap even) then quickly dry it so it doesn't flash rust.