Life-saving air bags pack deadly chemical

Sodium azide in discarded air bags may be an environmental hazard, says a University of Arizona researcher

By Environmental News Network staff

April 4, 2000
Web posted at: 12:16 p.m. EDT (1616 GMT)

Automobile air bags save lives — possibly at the expense of human health and the environment, says a University of Arizona researcher.

Eric Betterton, a professor of atmospheric sciences at the university, maintains that air bags utilize a deadly chemical. Betterton is concerned about the likelihood of toxic spills and spoke about the issue at the national meeting of the American Chemical Society.

For the past several years, the researcher has worked with undergraduate students to learn more about the ecological impact of sodium azide, a substance used to inflate air bags at the moment of impact in an auto accident.

Sodium azide, which looks like ordinary table salt, is a potent poison that can kill anything from soil bacteria to humans.

A mere 50 milligrams — less than two thousandths of an ounce — of the toxin can put a human into a coma within five minutes. A few grams will kill a person in less than an hour, according to Betterton.

The researcher knows some of the effects of sodium azide from personal experience. Betterton accidentally inhaled the substance during a laboratory experiment in graduate school.

Studies performed by scientists in the 1970s also reveal that sodium azide can wreak havoc on the environment. "At a high enough concentration, it can kill (soil) bacteria, plants and even seeds of plants," said Betterton.

Scientists are not clear about how sodium azide is metabolized. "Practically nothing is known about the environmental chemistry or biology of azide," Betterton said. But its deadly qualities are nothing new, as the substance has been used in broad-spectrum industrial biocides for many years.

Unfortunately, researchers do know if sodium azide is water-soluble. "Spills therefore could potentially migrate into sewers, streams, lakes and groundwater systems," Betterton said.

The general public does not know that trucks carrying sodium azide regularly travel U.S. highways. Nor do people know the chemical is used in air bags and that no standard has been set for the safe disposal of the toxic substance as it sits in discarded cars and trucks.

"As the demand for air bags increases, and as vehicle fleets age over the next few decades, the amount of sodium azide that could potentially be released to the environment will greatly exceed the approximately 5 million kilograms (11 million pounds) that has already been incorporated into inflators in the United States alone," Betterton said. "Given the huge surge in production, there exists a greatly increased potential for significant accidental spills and subsequent human exposure to this material."

When a vehicle equipped with air bags is involved in an accident, a special mechanism is triggered that heats tablets of sodium azide contained in a canister within the air-bag. A chemical reaction occurs that causes the sodium azide to decompose explosively, forming harmless nitrogen gas and metallic sodium.

Though metallic sodium is dangerous and can cause burns, manufacturers blend silica and iron oxide to make the air-bag byproduct less active chemically, reducing its harmful qualities.

Since air bags are relatively toxin-free after they have been used, Betteron advocates regulations that require deployment of the bags when a car is sent to the dump. This would protect against the release of sodium azide into the environment in the event the car were crushed or left in the junkyard to rot.

Betterton and his students have been looking for naturally occurring substances that rapidly detoxify sodium azide. The best they have found is ozone, but concentrations in the air are too low to be of much help, Betterton said.

The good news is that air-bag manufacturers are beginning to phase out sodium azide and implement other technology to inflate them, including compressed nitrogen and combustible gases that use a highly controlled explosion to fill the bag.

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Eric Betterton American Chemical Society Atmospheric Sciences Department
The University of Arizona
sodium azide

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