Environmental Fate of Sodium Azide Derived from Automobile Airbags

Abstract

The environmental fate of sodium azide (NaN3) is of considerable interest given the recent surge in production to satisfy demand for automobile air bag inflators, where it serves as the principal active ingredient. Since the mid-1990s, demand for sodium azide has exceeded 5 million kg per year and most passenger vehicles sold in the United States now contain approximately 300 g (≈0.7 lb) of sodium azide. This has greatly increased the potential for accidental environmental releases and for human exposure to this highly toxic, broad-spectrum biocide. It can be argued that a new environmental threat has developed because not only are millions of kilograms of sodium azide now transported to and processed at air bag inflator factories, but also this substance is now widely distributed throughout the developed world in automobiles. Even if sodium azide were to be replaced by a more benign propellant in the future, the problem of safely disposing of large quantities of azide will remain as the vehicle fleet ages and is retired to scrap yards and shredders. Unfortunately, the environmental fate of sodium azide is unknown so it is difficult to effectively manage releases. The problem is compounded by the fact that aqueous sodium azide is readily hydrolyzed to yield hydrazoic acid (HN3), a volatile substance that partitions strongly to the gas phase.