Forensic Chemistry: IED Four-Component Model and Types

UGC-NET Forensic Science Unit VI drill covering the four-component model of improvised explosive devices (IED) and the principal device types encountered in Indian case work. The four-component model -- initiator, main charge, switch, and power source -- forms the analytical framework for every IED investigation and render-safe operation, and mastery of each component's function, position in the explosive train, and forensic signature is tested across Questions 1 to 5.

Questions 6 to 14 cover the two most common container-based IEDs in Indian forensic case work: pipe bombs (galvanised iron pipe, threaded end-caps, low-explosive fill of smokeless powder, black powder, or match-head composition) and pressure-cooker bombs (sealed aluminium vessel, ammonium nitrate main charge, anti-personnel shrapnel of nails and ball bearings). The confinement principle -- tighter casing equals higher internal pressure equals more violent rupture -- runs through both sections. Post-blast indicators including end-cap thread marks, locking-lid lug geometry, and gasket fragments are highlighted as device-typing evidence.

Questions 15 to 19 focus on tiffin bombs (stainless-steel tiffin-box containers), with specific reference to the 13-bomb Mumbai serial blasts of 12 March 1993 and the 26/11 Mumbai attacks of 26 November 2008, where tiffin boxes and bag-borne IEDs with RDX main charges were confirmed by Central Forensic Science Laboratory examination. Questions 20 to 23 examine nail and shrapnel bombs and the forensic comparison of shrapnel to suspect possession. Questions 24 to 27 address vehicle-borne IEDs (VBIED), payload advantage, and Vehicle Identification Number (VIN) recovery as a device-to-purchase-chain link. Questions 28 to 30 cover render-safe procedures including the Bomb Disposal Squad (BDS) cordon-first protocol, the water disruptor (Pigstick), the hook-and-line repositioning technique, and X-ray fluoroscopy triage.

Topics covered:

• IED four-component model: initiator, main charge, switch, power source
• Explosive train sequence and render-safe interruption logic
• Pipe bomb: GI pipe, end-caps, smokeless powder and match-head fill
• Pressure-cooker bomb: sealed vessel, ammonium nitrate fill, nail and ball-bearing shrapnel
• Tiffin bomb: stainless steel container, 1993 Mumbai blasts, 26/11 Mumbai
• Nail and shrapnel bomb: fragmentation physics and shrapnel comparison evidence
• VBIED: payload advantage, VIN recovery, post-blast scene investigation
• Render-safe: BDS cordon-first protocol, water disruptor, hook-and-line, X-ray triage

Allow 30 minutes.