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Hazard

Release or spill of corrosive material

Hazard Knowledge

Corrosive materials cause visible destruction of, or irreversible alterations to, living tissue by chemical action at the point of contact. Corrosive materials include acids, bases, alkalis and salts. The pH scale ranges from 0 to 14, with strong acids having low pH values and strong bases or alkaline materials having high pH values. A neutral substance would have a value of 7.

Acids are compounds that form hydrogen ions in water. These compounds have a pH of less than 7, and acidic aqueous solutions which will turn litmus or pH paper red. Materials with a pH of less than 3 are considered strong acids. Inorganic acids such as nitric, sulphuric, hydrochloric and hydrofluoric acid can cause severe tissue burns to the skin and permanent eye damage. Many acids react and corrode various metals to produce hydrogen gas, but whether a particular reaction will occur or not depends on the particular acid and metal concerned and also on the conditions. The hydrogen produced is lighter than air and likely to produce flammable/explosive atmospheres in confined spaces. Acids will produce carbon dioxide from a carbonate (e.g. sodium carbonate or ‘soda ash’). Acids are neutralised by bases (or alkalis) to give only salts and water. Note that this could potentially be a violent reaction.

Bases (or alkalis) are compounds that will react with acids to but can also be corrosive. These compounds have a pH of more than 7, and alkaline solutions will turn litmus or pH paper blue. Materials with a pH greater than 11 are considered a strong base. Bases (or alkalis) such as sodium hydroxide and potassium hydroxide are corrosive because they break down fatty acids in skin tissue and penetrate deeply.

Acids generally cause greater surface-tissue damage and bases (or alkalis) produce deeper, slower healing burns. Inhaled corrosive gases and vapours can cause acute swelling of the upper respiratory tract and chemically-induced pulmonary oedema. Highly water-soluble materials, such as anhydrous ammonia, will affect the upper respiratory tract and since they are very soluble, they will attack skin readily, especially in sweated or wet areas. Less water-soluble materials, such as hydrogen sulphide and phosgene, will affect the lower respiratory tract. Lower respiratory tract injuries can lead to chemically-induced pulmonary oedema and may be delayed for up to 48 hours after the exposure.