Sodium azide, the chemical that inflates auto safety air bags, is nasty stuff. It is highly flammable, often explosive and extremely toxic. It is so sensitive, in fact, that large explosions have been set off by workers performing such innocuous tasks as placing a wrench on a bolt or using a metal scoop near the chemical.

People who work with sodium azide must not breathe it or allow it to contact their skin. At moderate- or high-exposure levels, the chemical creates respiratory distress, including pulmonary edema, a condition that fills the lungs with fluid, sometimes causing a victim to drown in his own liquids. Lower-level exposure produces heart-function irregularities, including enormous drops in blood pressure and occasionally cardiac arrest.

Long-term exposure to the chemical has been shown to cause mutations in plant and animal genes. For years it has been suspected of being a carcinogen to humans, but the few studies in that regard have been inconclusive.

Sodium azide can behave unpredictably in the presence of other substances. When it comes into contact with an acid, or even water that is slightly acidic, for example, it creates hydrozoic acid.

Hydrozoic acid gas is extremely toxic--one moderately strong whiff can cause convulsions and death. It has been extensively tested on laboratory animals, and its effects on humans are detailed in papers found in Nazi prison camps at the end of the Second World War.

Toward the end of the war, the Germans considered using it as a chemical-warfare agent.

TRW Vehicle Safety Systems in Mesa uses large amounts of sodium azide to make the safety air-bag systems installed in new automobiles. Something like five million pounds a year.

Safety and TRW, however, definitely are not synonymous.
While working with the chemical, TRW employees and subcontractors have started at least two dozen fires and explosions at the company's two East Valley plants.

TRW has improperly stored tons of sodium azide in Mesa for years. The company has failed to build safety systems it had promised to win approval for one of its Mesa plants.

And documents show that the company is putting large amounts of the chemical directly into the Mesa sewage treatment system, a practice which some experts say could have deadly results.

In the wake of a recent explosion that killed one worker and critically injured another, TRW has quite deservedly gotten bad press. Even the government has been critical.

But the City of Mesa and the State of Arizona have known about serious problems at TRW for a long time. And those governments have done virtually nothing to fix the problems.

In fact, over the past few years, the City of Mesa has been a very good friend to TRW Vehicle Safety Systems.

If you get in a front-end accident in a car equipped with air bags, here's what happens: Electronic sensors mounted around the front of the car measure its deceleration. If it is severe enough, an electric charge is sent back along the steering column and into the air-bag inflator assembly, nestled in the steering wheel beneath a carefully folded and packed bag.

The jolt of electricity sets off a booster charge, which triggers the detonation of a stack of propellant disks arranged around the core of the unit. Think of the booster charge as a blasting cap and the disks as dynamite.

The disks are extremely volatile and burn instantly, releasing a large amount of nitrogen gas as they are consumed. It is this gas which leaks out of the inflator assembly and fills the bag. If everything goes according to design, the bag instantly inflates, cushioning your upper body and keeping you from slamming into the steering wheel and windshield.

In order to be effective, the detonation and inflation of the bag must take just 40 thousandths of a second. Obviously, the propellant used to inflate air bags has to be extremely volatile; otherwise, it couldn't burn quickly enough to work.

The principal ingredient in air-bag inflators is sodium azide. Until recently, this chemical was used in small quantities as a laboratory preservative, in larger quantities as the inflating agent for airline emergency ramps and in even larger quantities by the explosive and munitions industries.

Now, though, the demand for air bags has skyrocketed, and manufacturers have been scrambling to boost production. Environmental and health researchers, charged with determining the chemical's possible hazards, have been kept just as busy.

Eric Betterton works out of a medium-size office on the fourth floor of the Physics and Atmospheric Sciences Building at the University of Arizona in Tucson. He is one of the few people in the country who have begun serious study of sodium azide and the environment. Because the chemical was not used widely until air bags became common automotive equipment, information has been hard to come by.

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Dave Plank