Sodium azide salt is very stable. Kept cool in a sealed container, away from moisture, it will keep indefinitely. Aqueous solutions of the salt (<5%) can also be stored in plastic sealed containers. However, neither the salt nor aqueous solutions should come into contact with metals because of the possible formation of unstable/ explosive compounds. Disposal of any unused salt or solution of the salt should not be made through the drainage system where contact with metal is a real possibility. Problems associated with handling and management of sodium azide have led to its description as a particularly dangerous substance.
In truth, nearly all the hazards associated with sodium azide are due to accidental formation of its chemical parent, hydrazoic acid, (HN3
). Hydrazoic acid is a volatile, weak acid. It is also a toxic, shock-sensitive explosive. Unlike the salts, hydrazoic acid can be absorbed through the skin. Even though the smell of hydrazoic acid is described as ‘extremely pungent’, ‘obnoxious’, and even ‘fear-inducing’, one may not always get adequate warning to protect oneself.
Should a spill of azide occur, this can be mopped up using a dilute solution of sodium hydroxide (lye, caustic soda), rather than water. The sodium hydroxide will prevent the formation of any hydrazoic acid by immediately converting any hydrazoic acid that may be present back to sodium azide. Gloves and other safety equipment are essential in such a scenario.