It was a cloudy morning at a Seattle hotel in 1994 when Paresh Khandhadia's 'Eureka!' moment came. It arrived in the form of a curled paper fax full of numbers that spooled out at the hotel desk at breakfast time.
Sent from Takata Inc.'s Automotive Systems Laboratory in Farmington Hills, Mich., the data proved that a new airbag inflator not only worked, but that its mix of gases would not be harmful to even an asthmatic passenger.
'I recall that very, very clearly. I was traveling to our plant site near Seattle, Wash. I had my team with me: an engineering manager, a couple of engineers. We sat down, actually after breakfast, we picked up the faxes, looked at the results (of lab tests) - and that was it. I said, 'Wow! This is the break!' ' says Khandhadia.
It was, literally, rocket science. Solid fuel pyrotechnics are, in essence, rocket propellant designed to give off gas but no thrust.
Hunched over the crumbs of breakfast and waving away hotel employees, the engineering team rapturously crunched the numbers from the Michigan lab and then fled to a room telephone for a conference call with Takata management.
'We were slightly late for our meeting that morning - but I think it was all worth it. These are some of the moments you never forget, and this was the moment.'
What Khandhadia, 40, a chemical engineer, had done was to lead development of an environmentally friendly 'non-azide' inflator.
Sodium azide has been, until recently, the key solid fuel propellant used to inflate airbags in microseconds. Stable and safe in its ultimate installation in inflator modules in vehicles, sodium azide creates nitrogen gas when ignited. Since nitrogen already makes up the bulk of the atmosphere, the gas raises few environmental questions.
But azide itself is nasty stuff. It has a distressing tendency to explode unpredictably during manufacture when exposed to air, light or jostling. Azide plants are designed, like chemical labs, with walls that fall open when an explosion happens. And sodium azide is toxic.
'Sodium azide is one of the most toxic substances known to mankind,' says Khandhadia. 'Azide is a Class B poison. The threshold limit value for exposure for human beings is 0.3 milligrams per meter cubed, or 0.1 parts per million. That's 100 parts per billion.
'On top of that, it's an unstable compound. I used to work on the azide side. You know, you would get this accident in the plant, and you try to duplicate it in the lab to get to the root cause, and you can never find it.'
The cocktail effect
Khandhadia, who'd been lead engineer for propellant development at Takata since 1993, knew he would face challenges in developing a non-azide inflator.
Working with a chemical family called tereazoles, he found himself carving out new research areas in analyzing the mixture of gases produced when the pyrotechnic charge went off.
'You look at the toxicity exposure and all the values you see in the literature are for individual gases. In our case, it was the mixture, the cocktail effect, that nobody had ever started to analyze. That's where we started,' Khandhadia says.
His team was trying not only to get a non-toxic gas mixture, but to avoid one more of azide's problems. When azide inflators discharge, they leave an alkaline dust residue in the passenger compartment. The dust may cause problems for some people with extreme breathing difficulties, including asthmatics.
'The major stumbling blocks were this effluent, and exposure issues in the passenger compartment of the car. The second major stumbling block, I would say, would be finding a combination of compounds that would give you this 'correct' propellant base, which would lead to this gas, which gives you a transference restraint performance.'
'Are you crazy?'
The technical challenges were huge, but even more daunting were the challenges of getting the auto industry to look seriously at a replacement for a system that already worked. Takata's 'Envirosure' tetrazole inflator, the result of the engineering team's success, was loaded with new patents when company salespeople began introducing it to automakers in 1995 for inclusion on 1998-model vehicles.
'Acceptance by our customers, that was one uphill battle,' Khan-dhadia says. 'As late or as early as four years ago, I would go to the customer and try to propose this and they would say, 'Are you crazy? What are you talking about?' '
Getting automotive suppliers to bite on the lure of a new product can be tough. In the cliquish and conservative automotive world, innovative failures resonate for a long time.
'Even when a new customer comes in, he doesn't want to be the first on the road with this. They want to have some other customer road-test it for five years before they will buy it,' says Khandhadia.
On the edge
When enough advantages stack up, though, automakers are willing to move.
'Though the auto industry is conservative, there are people who are prepared to take a chance. And from my point of view, having worked in other industries, I should say the auto industry is always looking for the new technological edge,' he says.
One major automaker, whom Khandhadia would not name, adventured into jointly carrying out human testing and 'due diligence' work with Takata. Khandhadia's inflators did not faze even the most asthmatic test subject. Some people even got out of the test cars saying they felt better than before.
A wave of non-azide inflators has come on the market in recent years, some influenced by Takata's success, others the product of parallel development at other companies.
The technology is widely accepted enough that some makers of 'hybrid' inflators, such as stored-compressed-gas modules, use the term 'non-azide' as a marketing plus to the automakers.
Khandhadia is intrigued, too, to find that 'green' engineering is again a hot topic.
'I don't want to say I'm a recent convert to green. Even before this, in my career, I have worked on some of the asbestos issues. I also worked in the urea-formaldehyde foams, where there was an indoor air pollution problem. (Green engineering) resonates so much with me,' he says.
Now executive director of Takata Advanced Restraint Systems Group's inflator and propellant development in Farmington Hills, Mich., he is proud of the non-azide device. He says it has brought not only more market share for Takata, but also closer relationships with customers.
'I'm hoping that next time around, when I go in with a new technology, it will be less of a hard sell,' he says.
'The people who work with the product know their product, and know the green effects. It becomes our job as an engineer to educate, or at least inform, our customer.'