A number of experts believe that bombs made from ammonium nitrate (AN) fertilizer have become a significant homeland security threat. If it were to be carried by trucks or limousines, an AN bomb, which has been illegally mixed with motor oil or diesel fuel, could cause massive destruction.

To prevent this from happening in the United States where eight billion pounds of AN move through the country annually, a joint effort by the Bureau of Alcohol, Tobacco, Firearms & Explosives (ATF) and The Fertilizer Institute is under way to develop effective detection technologies that will enable prompt reporting of suspicious shipments of bulk AN. The highly classified technologies undergoing testing include vapor and particle sensors, chemical luminescence, pulse-fast neutron, gamma-and-x-ray analysis—and a $500,000 'car bomb finder' that has achieved 95% accuracy and is able to analyze a vehicle in as little as 30 seconds.

The Department of Homeland Security reports that trace-portal screeners, also known as "puffer machines" after the puff of air that gently hits passengers to detect explosives, are being tested at seven airports. Whereas backscatter x-ray technology is being tested using low-power, x-ray generators to penetrate substances, including clothing.

But backscatter technology is not without its critics, because x-ray exposure and privacy issues need to be resolved. Nonetheless, it is being tested at the 1815-foot high Canadian National Tower in Toronto, the world's tallest building, and at Heathrow airport near London, as well as at several nuclear sites in the United States.