Yesterday, the National Highway Traffic Safety Administration announced that it has expanded its investigation into defective Takata airbags that have prompted the recall of more than 19 million vehicles manufactured by 12 automakers. The airbags—as you can see in this dramatic video shown during yesterday’s briefing—sometimes explode instead of inflate, showering passengers with potentially deadly shards of plastic and metal.

The number of recalled cars stood closer to 8 million one year ago, but the investigation continues to pull in more airbags and potentially affected vehicles. Originally, regulators focused on driver and front passenger airbags, but they now will investigate side airbags and newer cars that weren’t included in the first pass. That means manufacturers may recall stilll more cars.

And that means they have to test even more, too. As the number of potentially affected vehicles expands, so does the type and quantity of airbags that must be analyzed. And while Takata has been conducting its own investigation of the root causes of its airbag failures, regulators have hired research organizations like Battelle—which filmed the video above of one of its airbag tests—to develop their own analytics.

Battelle in particular is working on large lot tests—procedures that allow it to test dozens of airbags in rapid succession, instead of one-off tests like the one above. “With such a catastrophic potential for failure, the only option is to test a large number of inflators,” says Ben Pierce, who runs Battelle’s transportation research group. While Takata might test 4,000 airbags in a week, Pierce says, Battelle’s procedure can run through a couple thousand in a day.

To develop those large-scale tests, Battelle uses a big blast chamber in West Jefferson, Ohio. Built of concrete, its domed structure has foot-thick walls to shield workers during airbag inflations and other high-energy tests, from examining hydrogen fuel tanks to analyzing ballistics. “We put rack after rack after rack of inflators in there and set them off one at a time,” says Pierce. “It’s loud: You can feel it, you can hear it. It’s disturbing, quite honestly.”

While the National Highway Traffic Safety Administration hasn’t explicitly tasked Battelle with identifying the root cause of the airbags’ explosive malfunction—just designing tests—its experimental procedures offer some hints. That domed blast chamber is outfitted with pressure sensors and slow-motion cameras, and every inflator Battelle tests gets a CT scan before ignition.

That CT scan is perhaps most likely to reveal information about the defective inflators. “The way an airbag works,” Pierce explains, “is there’s a charge that builds pressure, and it launches the airbag out.” That charge is a small wafer of ammonium nitrate, and it’s not supposed to be explosive—it’s simply supposed to expand rapidly as a gas, propelling the airbag out.

But in a certain proportion of Takata’s airbags, “there’s some reason that that explosive charge, instead of launching it normally, it ruptures the metal wall of the container that’s holding the charge,” says Pierce, creating hazardous shards just a foot or two from passengers. In the course of creating its high-throughput tests, Battelle has noticed that wafers that are deformed or larger than usual—as they appear in those pre-test CT scans—are more likely to rupture violently.

Takata has emphasized the role of degradation in the defects; its internal tests suggest that high heat and humidity can degrade the ammonium nitrate wafers over time, potentially leading to failure. But a recent side airbag rupture in a 2015 model Volkswagen calls that explanation into question. Neither Takata nor regulators seem to know exactly what’s behind the failures—and the only path forward is lots more pyrotechnics.

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Watch Takata’s Defective Airbags Explode in Slow Motion