Muriatic acid is a form of hydrogen chloride gas. It is used in an aqueous form and has an unpleasant odor. Its fumes can be highly toxic when they are released into air. Volcanoes spew muriatric acid into the air during eruptions. Because it is a strong, corrosive, inorganic, mineral acid, one of its primary uses is removing rust. It can be used to remove rust from a wide variety of objects and substances. Great care, however, must be taken in doing so.

Corroded metal surface
credit: Hemera Technologies/ Images

Safety Issues

Because of muriatic acid's highly toxic nature, using it to remove rust, though effective, is not the easiest of tasks. It is safe for humans only when it is diluted. At high levels of dilution, however, it is hardly effective. It is extremely effective when used in its raw form, but using the acid in this form to remove impacted rusts also can pose health hazards, such as irritation of the skin and burning of eyes. It also can cause serious burns in body tissue as well as major respiratory problems, apart from causing death when ingested in its undiluted form. As a result, the U.S. government has classified muriatic acid as a poison under the Federal Caustic Poison Act.

Instructions for Use

If you are going to use muriatic acid to remove rust despite the heath risks, dilute it 1 to 10 with water. Work in a well-ventilated space, and wear dark glasses and gloves. Place the diluted water-acid mixture into a spray bottle, and spray it on the rust. Use a brush to scrub off the rust. Then, because of the power of the acid, the material has to be immersed in water to take off the remaining acid. If rust still remains, the process can be repeated. After the rust has been removed and the item dipped in water, the effect of the acid has to be neutralized further by using water and baking soda.


Because muriatic acid is so highly dangerous, after it has been used it needs to be disposed of in a safe and healthy manner. Anyone who has used this substance is obliged to abide by rules governing safe disposal of biohazards. While these rules vary from state to state, generally, it must be disposed of in a special biohazard container and labeled as biohazardous. It also usually must be taken to a special waste drop-off and cannot be put out with your regular garbage for pickup.