I have a 1 gallon plastic bottle of muriatic acid which lives in my basement where my shop is located. In more than forty years,I haven't had a rusting problem with my machines or tools. I keep the bottle tightly closed. If an open container is present, HCl fumes do escape. If HCl fumes are suspected, an open container of ammonia will quickly show them. The two combine to form NH4Cl, a dense white fog that settles on everything as a white dust. Applying even diluted HCL to a surface like a floor is another thing. It will all eventually dissipate as vapor and react with any metal surface.
HCl fumes are also dangerous to the respiratory system. Fortunately, exposure results in a severe cough which usually makes one take corrective action..
I worked as an analytical chemist for six years where we literally boiled away a half gallon of HCl each day.The procedure was carried out in a fume hood but with that amount of acid, some fumes made it out into the lab.
As with all chemicals, they need to be used with some knowledge and respect rather than fear. Proper PPE, understanding the chemistry, and and knowing what to do in the event of accident is paramount.
