11.4 Notes

High Explosives Classified into two groups Primary explosives – detonate violently with no burning Used as primers – detonate other explosives via chain reaction Rarely the main ingredient in homemade bombs Secondary explosives – normally burn rather than detonate Comprise mostly of commercial and military blasting Dynamite, TNT, PETN, RDX, tetryl

Industrial Explosive Market Moved from nitroglycerin based dynamite to ammonium nitrate based Water gels, emulsions, and ANFO explosives Mix oxygen-rich ammonium nitrate with a fuel to form low-cost, very stable explosive High explosives must be detonated by an initiating explosion such as blasting caps composed of copper or aluminum filled with lead azide

Types of High Explosives ANFO is ammonium nitrate soaked in fuel oil Widely used in mining Readily available for homemade varieties due to abundance in fertilizer TATP = triacetone triperoxide Made with acetone, hydrogen peroxide and hydrochloric acid Extremely potent when confined in a pipe Used by terrorists groups in Israel and the Middle East

RDX – cyclotrimethylenetrinitramine Most powerful military explosive Often in the form of a plastic doughlike substance called a C-4 PETN – Pentaerythritol tetranitrate Used by the military for small-caliber projectiles and grenades Commercial used as a detonating cord Used to interconnect a series of explosive charges so that detonation is simultaneous

Collection and Analysis of Explosives Most important is the collection of samples from the explosion scene Determination of high or low explosive is the presence of a crater at the origin of the blast Locate crater and remove loose soil and debris in the crater to be preserved Wire mesh screens are used for sifting debris Objects near the source must be collected and checked for penetration or residuals on the surfaces

Use of the IMS (ion mobility spectrometer) A vacuum to collect explosive residue from surfaces with additional surface residue wiped down with a paper disc The residues are vaporized and converted to electrically charged ions Used as a screening test All materials placed in sealed containers Soil and soft loose materials stored in metal containers or plastic bags

In the lab Microscopic examination for particulate recognition Rinse in acetone and analysis with TLC and then GC/MS If it is a low explosive then a rinse in water Confirmation tests include IR Spec; X-ray diffraction

Proposed Taggant program Color coded chips added to commercial explosives Chips are fluorescent and magnetic sensitive Color indicates where the explosive was made and produced Allows for a trace through distribution chain Only now used in Switzerland ICAO (International Civil Aviation Organization) has mandated volatile taggants be added to plastic explosives

11.4 Questions What is a detonator? What is the composition of most detonators? Name three military high explosives. Which is the most powerful and popular of these explosives? What is the most obvious post-explosion characteristic of a high or contained low explosive? What device is widely used to screen objects for the presence of explosive residues? How are soil and other soft loose materials collected at the scene of an explosion best stored? What is the first procedure typically used to analyze bomb-scene debris that arrives in the laboratory? What does the forensic scientist do to explosive debris following microscopic examination? Why? List three procedures commonly used as screening tests for explosive residues. What is a taggant? What purpose do taggants serve?