Etching solution vs muriatic acid to prep concrete for epoxy
I use muriatic in confined spaces, yes it is bad and needs to be vented. You are the highest risk when diluting the acid. Always add acid to the water, a 70% water 30% acid will do just about any floor. If it is clean , just needs to be etched I have used 15% acid with good results, when it quits bubbling the acid is close to consumed by the reaction.  (Note this is by volume I think the acid available at home stores and pool supplies is 36% if some one wanted to get technical so the real value is only about 10% acid).