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Journalism of Courage
The pressure-cooker bomb,back in focus with the Boston marathon blasts,has been a preferred device with attackers partly for its handiness and largely for its compactness,say Indian counter-terrorism and forensic experts long used to investigating such explosions.
Does it have an added advantage as an improvised explosive device? The answer is no, says a forensic expert. The advantage is in its construction.
Central forensic lab director C N Bhattacharya,however,says,There are many ways one can tightly pack IEDs. The pressure cooker is nothing but a container,and terror groups use a variety of methods.
A pressure cooker does offer a compact space to arrange an IED,with a tight lid. One difference from other containers is the readymade hole for the ignition wire, says an expert. It is also rust-proof,ensuring the chemicals work well.
Until the 2006 train blasts of Mumbai 7/11 brought pressure-cooker bombs into wide focus,investigators looked at IEDs as raw,unsophisticated and even hurriedly assembled bombs,never associating them with meticulousness. A pressure-cooker bomb in such circles is simple,probably the most simple,but it speaks of meticulousness,and of neatness, says a forensic scientist. On its own,it is not exceptional.
Incidentally,the 7/11 chargesheet says the IEDs were placed in a household utensil,without mentioning pressure cookers specifically. The recoveries were parts of a black cloth,and brittle remnants of a container. Experts and investigators differ whether the container was indeed a pressure cooker. Some argue the bombers initially practised with milk cans,but the loose lid was proving weak. It was not multidimensional either,with the energy always released in the direction of the mouth.
A pressure cooker,on the other hand,keeps chemical reactions contained,leading to a multidimensional explosion. Once activated,a shock wave causes chemical bonds in the charge to break up,leading to an instantaneous buildup of heat and gases. These flow outwards,towards the undetonated explosives,at high velocity,pressure and temperature, says a senior official with the National Institute of Forensics Science and Criminology. The container then explodes at temperatures around 3000C,the effect estimated at 7,000 miles per hour,says an NIA expert.
They continue to be used for the compression they offer. Getting the direction of energy release right is the most important point, says Dr Rukmani Krishnamurthy,chairman and CEO,Helik Advisory Ltd,and former director of Maharashtras forensic lab. She recalls the technique of blasting IEDs inside a compressed,thick-walled container being used back in 1983,when such a bomb had exploded in the office of textile union leader Datta Samant.
The pressure-cooker bomb is a complete IED. No resource is wasted. The container itself disintegrates and the shreds are projected as missiles, says a forensic expert formerly with the National Security Guards.
The pressure cooker itself acts as shrapnel, agrees Karnal Singh,who headed the Delhi police special cell and handled the probe into a number of pressure-cooker bomb attacks in 2005 and 2006. Making such bombs does not require much expertise or training.
The pressure cooker also has the advantage of deception,as the almost perfect camouflage. Until 7/11,security personnel never asked you what you are carrying in the pressure cooker, says an IPS official who,after those blasts,had promptly added pressure cookers in the must check list across road nakabandis.
One expert highlights a novel contrast: In some cases a pressure-cooker bomb has caused fewer casualties as it usually has low-intensity explosives that need tight confinement. High-intensity explosives work in any setup.
With inputs by Rahul Tripathi in New Delhi
