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A corrosive substance is one that will destroy or irreversibly damage a substance, including living tissue, by chemical action (rapid corrosion of living tissue). The main hazards to people include damage to eyes, skin and tissue under the skin, but inhalation or ingestion of a corrosive can damage the respiratory and gastrointestinal tracts.
A low concentration of a corrosive substance is usually an irritant. Corrosion of non-living surfaces (metal, etc.) is a distinct concept. For example, a water/air electrochemical cell corrodes iron to rust. However, in the Globally Harmonized System, rapid corrosion of metals also qualifies for the "corrosive" symbol.
Common corrosives are strong acids and strong bases, or concentrated solutions of some weak acids and weak bases. Their action on living tissue is based on acid-base catalysis of ester and amide hydrolysis. Both corrosive acids and corrosive bases are able to defat skin, because they catalyze the hydrolysis of fats (fats are chemically esters). Proteins are chemically amides, which can also be catalytically hydrolyzed by acid-base catalysis. Strong acids and bases also hydrate easily, which removes water from the tissue and is significantly exothermic. For example, concentrated sulfuric acid causes thermal burns in addition to chemical burns.
There are also examples of more specific corrosives. Hydrofluoric acid, for example, makes initially painless burns but easily permeates tissue to selectively attack bone. The word 'corrosion' is derived from the latin verb corrode which means 'to gnaw' indicating how these substance seem to 'gnaw' their way through the flesh.
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