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A Bomb-Proof Bag to Foil Terrorists

How can a bag be bomb-proof? Try coating it with a bizarre fluid that hardens under sudden force.
July 8, 2011

In November, a suitcase was nearly loaded onto the hold of an Air Berlin flight bound to Munich from Namibia. At the last moment, an x-ray scanner uncovered some anomalies in the suitcase–namely, it contained a device made up of batteries, wires, a fuse, and a ticking clock. Though ultimately authorities determined there were no explosive materials in the device, Spiegel Magazine reported that the event could have been a dry run by terrorists looking to sneak a bomb into the hold of an airplane.

The most frightening attacks on airplanes in the past decade have mostly happened in the passenger cabin. But the luggage hold, beneath the cabin, is another possible point of attack–it was the method of the Lockerbie killer, for instance, and events like the Air Berlin near-miss have led onlookers to wonder if it could happen again.

To guard against such an event, an international team of scientists have developed a special bag that they say would quell an explosion in a plane’s hold. Developed partially by University of Sheffield scientists working at the university’s spin-out company Blastech Ltd., the Fly-Bag, as the invention is called, relies on the bizarre properties of substances called “shear-thickening fluids.”

Shear-thickening fluids, whose properties are so strange they earn the moniker “non-Newtonian,” increase in viscosity when under great strain. A simple shear-thickening fluid can be made by combining cornflour with water, Sheffield informs. Get the ratio just right, and you’ll have a substance that will remain a fluid when left alone, but will turn rigid and behave like a bouncing ball if you throw it against concrete. Explains Sheffield: “Under normal circumstances, the particles in STFs repel each other slightly, however following sudden impact, the extra energy in the system proves stronger than the repulsive forces, causing the particles to clump together in structures called hydroclusters, which bump into each other, consequently thickening the fluid.”

The wonder material has inspired many researchers to mull defense applications. Last summer, UK scientists developed “liquid armor” using shear-thickening fluids. They called it “bullet proof custard,” and praised it for having the properties of bullet proof vests, only with much less weight and bulk. The properties of shear-thickening fluids lead to the strange result, however, that while such a vest would defend against a sudden, aggressive knife attack, it wouldn’t guard against a slowly piercing one.

There’s no such thing as a slow explosion, however, which means the Fly-Bag has fewer vulnerabilities. Made up of elastomers coated with those shear-thickening fluids, the fabric of the bag goes suddenly rigid when it comes under strain. As with the vests of “bullet proof custard,” the main advantage here is weight and convenience. Armored luggage containers already exist, but they’re bulky, expensive, and only work in aircraft with wide bodies. The Fly-Bag mitigates all those problems, and is expected to be on the market inside of two years.

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