bombing had used it.
Ammonium nitrate is widely used as a fertiliser and the fuel oil (Anfo) could either be diesel, kerosene or molasses. Anfo is widely used in mining, quarrying and civil construction. It is, therefore, impossible to control the sale of Anfo or keep an eye on the purchasers.
It is difficult for the security agencies to detect the manufacturing of IEDs since the components — explosives, detonators, trigger circuits, power supplies, timers — are easily available in the market and have other legitimate uses.
The power supply to such bombs comes from batteries and the trigger circuits are usually cellular and cordless phones, transistor radios, remote control toys etc. For building timers, terrorists use electronic circuits like quartz circuit watches.
The electrical ends of a receiver circuit (like a cellphone) are placed inside plastic explosive or the detonating cap and the terrorist, who may be several kilometres away from the site, can push a button on a transmitter circuit (cellphone) to send the signal to a receiving device. The receiver circuit then produces an electric current to detonate the explosive.
Even other plastic explosives such as RDX (Research Department eXplosive, chemically cyclo-tri-methylene-tri-nitro-amine), PETN (Penta-erythritol Tetra-nitrate), Semtex (a mixture of RDX and PETN) can be made easily. RDX is manufactured by fusing concentrated nitric acid (available in any school laboratory) with hexamine, which is widely used as a medicine as well as an industrial chemical.
Purchasing large quantities of hexamine would not arouse any suspicion since it is used as an antibiotic for treating urinary tract infections and in brake and clutch linings. PETN, which is a very powerful explosive, is even more easily available since it is used as a heart medicine.
Plastic explosives are almost impossible to detect; even metal detectors cannot do the job. If an expert makes them, they will be odourless and can be moulded into any shape. Even if they are made in a makeshift laboratory, they will smell like vegetable or fruits. Even trained sniffer dogs find it difficult to differentiate them from food products.
Only very expensive tests (Neutron Activation Analysis, Gamma Ray Irradiation, Laser Spectroscopy) can detect such chemicals. But they also require an expert to go very close to the suspected explosive. These expensive detectors can at best be used at entrances of airports or VIP security zones.
It is also difficult to prevent IEDs from exploding. Most VIP zones and motor convoys are protected against Remote Control IEDs (RCIEDs) by electromagnetic jammers that emit high power radio waves. If radiowave power is higher than the signals transmitted by the terrorist, they will jam or prematurely detonate the IED.
But if a terrorist brings an RCIED within the range of a jammer, the RCIED could explode. While the VIPs would be saved, there could be many civilian casualties. Also, since the best jammers work between 20 Hertz to 2,000 MegaHertz, they would interfere with cellular phones, TV and radio signals.
The political blame-game being played over the Mumbai blasts are misplaced since it is impossible for even the best intelligence agencies to detect and prevent such terror attacks. In an asymmetric warfare, the advantage lies overwhelmingly with the attackers.
It would require thousands of security personnel to be on high alert round the clock to prevent one single terror attack. Out of a thousand attempts, a terrorist needs to succeed just once; in contrast, the security agencies need to succeed every single time.
(Ravi Visvesvaraya Prasad heads a group on Command, Control, Communications, Computers, Intelligence, Surveillance, Reconnaissance, and Targeting in South Asia. The views expressed by the author are personal)