Monday, November 24, 2014

Takata's little bombs - engineer: "Won't that blow up?"

Detonation of an improvised explosive device 
made from airbag inflator substance used by Takata - ammonium nitrate.

This is not what happens inside an airbag. But it illustrates the explosive power of the unstable chemical Takata used, basically, a type of fertilizer that is very easily converted to indusrial explosives and bombs.

Not knowing much about explosives, curiosity overtook me, and I checked into ammonium nitrate, the cheap explosive that Takata chose to use for its airbag inflators that were used in Toyotas and many other vehicle makes.

I think it is highly unlikely that automaker engineers would not know what explosive substance was being used in the airbag inflators. If they knew, why are they not sharing legal responsibility? If they did not know, did Takata mislead them? Or did the automakers not ask? If they did not ask at the vehicle design stage, then they should share the liability. I am reminded of Toyota's failure to ask about the source code in its watchdog computer chip.

Senator McCaskill faulted Takata for the long time that it did not inform its customers about the defect, but I think that is expecting too little of the safety obligations of the automakers.

The New Yorker: the-fertilizer-bomb
"If a lot of energy is needed to split the two nitrogen atoms and break those bonds [of a highly stable N2 molecule] then, conversely, a lot of energy is given off when two nitrogen atoms come together to make the bond. The nitrogen atoms go from a less stable, high-energy state (such as in NO3 or NH4), to a very stable, low-energy state (such as in N2), with the excess energy being released very rapidly, even explosively. It’s not a coincidence that many of the most famous bomb-making chemicals—nitroglycerin, nitrocellulose, trinitrotoluene (TNT), and C4 plastic—are nitrogen compounds."
"So why doesn’t ammonium nitrate explode spontaneously? Because of something called activation energy, which is defined as the minimum energy necessary to start a chemical reaction. Ammonium nitrate’s activation energy is just high enough that it will not explode in everyday use. But provide it with a source of energy, like a flame, spark, or even mechanical impact, and the results can be explosive. “The ammonium nitrate has its own fuel, the ammonium, and its own oxidizer, the nitrate,” making the process self-sustained, explained Jimmie Oxley, chemistry professor at the University of Rhode Island. It’s because of ammonium nitrate’s explosive potential that the Department of Homeland Security proposed an ammonium nitrate registration program in 2011, to regulate transactions involving the sale or transfer of ammonium nitrate at the point of sale."

This diagram illustrates the various chemical phases of ammonium nitrate, and not being a chemist, I understand these on a simple level to mean that the molecular geometry of the compound changes according to density and temperature. It stands to reason that the explosive force may change in accordance with the change of geometry. Anyone can find this in 10 seconds on the Internet. Certainly it would have been easy for automaker engineers to understand.

Here's another tidbit: 
Unstabilized ammonium nitrate continues to grow bigger with each temperature cycle between room temperature and freezing and between room temperature and 120 degrees FThe middle cylinder in the picture to the left shows what happens to a composite propellant with unstabilized ammonium nitrate.. The cylinder on the right is phase stabilized with Dr. Oberth's formula using 3% zinc oxide. It is its original size after a month of temperature cycling. The cylinder on the left was "stabilized" with Urea which obviously was less than successful.
And the NY Times investigative article, quoting Takata engineers:

Why did they not ensure it would stay in the same phase? It seems this was a combination design and manufacturing defect, a terrible problem that arises in quality control in a far-flung global manufacturing operation

Questions: Why have automakers accepted legal responsibility for other kinds of defects, but Takata is on its own? Could Takata be taking the fall for its automaker customers in exchange for their support and continuing business, as would be expected in Japan?