Is there poison in auto air bags?

November 17, 2006

Dear Cecil:

In Judith A. Jance's mystery novel Partner in Crime (2002), the murder weapon is sodium azide, a chemical used in auto air bags. She got her story idea from a magazine article about how poisonous sodium azide is. The chemical is not deactivated when cars are sent to junkyards. Since this book was written, has anyone cared enough to address this problem in our environment?

Let's put it this way: some thought has been given to it. This shows you the benefit of stringent environmental regulation. In the old days, people would use chemicals with nary a clue about whether they were toxic. Now we know damn well.

Judith Jance covers the basics of sodium azide (NaN3) in her book. It's a white, odorless crystalline solid resembling salt. It's highly poisonous, and when added to an acid, or just acidic water, turns into a toxic gas with a sharp odor. The chemical's toxicity makes it useful as a pesticide and as an antibacterial preservative in hospitals and laboratories. Sodium azide reacts violently when it touches certain common metals, making cleanup in the lab pretty entertaining - if you pour it down a metal drainpipe, it explodes.

This explosiveness is put to use in auto air bags. On impact, a trigger mechanism detonates a small hunk of sodium azide, releasing a large amount of nitrogen gas and inflating the bag in the split second before your forehead would otherwise crater the windshield. Elemental sodium is also produced, which immediately reacts with other ingredients to form an inert silicate, fortunately for the car's occupants - sodium can be nasty too.

Daredevil as all this sounds, sodium azide is more dangerous when it's not exploding in your face. The compound can kill when inhaled in powdered form, drunk as a contaminant in water, or absorbed through skin contact. There is no known treatment other than alleviating symptoms until the crisis passes, assuming it does. Effects depend on the route and amount of exposure, ranging from dizziness, headache, and vomiting to hypotension, convulsions, respiratory failure, and death.

Sodium azide can also be lethal when released into the environment. It kills waterborne bacteria even in weak solution - a good thing when controlled, not so good otherwise. At 10 parts per million in soil it will kill or degrade seeds, and at 200 ppm it kills bacteria and fungi. It's readily water soluble, and its derivatives can easily spread through the water table into streams, rivers, and drinking supplies, potentially killing anything from single-celled life to us.

The good news about sodium azide, such as it is, is that it's a known danger. It's on the Environmental Protection Agency's "P-list," a designation for commercial products that qualify as acutely hazardous waste when discarded and thus can't just be tossed into the trash.

You're thinking: if this stuff is the chemical equivalent of the monsters from the Alien movies, why do they put it in cars? First, it works. A sodium azide-powered air bag inflates in less than 50 milliseconds, no small feat; alternative technologies have often been slower, less reliable, etc. Second, when the bag is deployed, the sodium azide promptly decomposes into harmless by-products. The Centers for Disease Control claim to have received no reports of sodium azide exposure following air bag inflation. Third, regulators apparently assume that when a car is junked its air bags are discharged or reused, either way presenting no danger.

Point three, unsurprisingly, is where things may fall down. Eric Betterton, a scientist at the University of Arizona who has studied sodium azide, has warned of the looming threat as millions of pounds of the stuff find their way into the environment. (UA grad Judith Jance learned about sodium azide from Betterton.) There have been numerous incidents. In 1994 a worker at an Arizona factory operated by TRW, the largest domestic maker of air bags, was killed by a sodium azide explosion. A truck carrying sodium azide overturned south of Salt Lake City in 1996, releasing a toxic plume that required evacuation of a nearby town. TRW has had repeated run-ins with state and federal regulators over leaks and improper disposal of the chemical.

More alarmingly, some have figured out sodium azide can be used as a weapon - an Arizona woman was convicted of using it in 2000 to poison her husband, and in 2003 Malaysian police said alleged terrorists were stockpiling it. Granted, in neither case was the stuff obtained from an auto junkyard, the scenario depicted in Jance's book. But the fact is, the P-list and the occasional stern warning notwithstanding, nobody really monitors what happens to undischarged air bags once a car reaches the end of the road. Automakers such as Toyota are phasing out sodium azide, but there's plenty still out there. While Jance's mystery novel may have raised the anxiety level, my guess is getting the authorities off the dime will take a series of unfortunate events.

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