468 CHAPTER 13

Among the high explosives, nitroglycerin-based dynamite has all but disappeared from the industrial explosives market and has been replaced by ammonium nitrate-based explosives (such as water .gels, emulsions, and ANFO explosives). In many countries outside the United States, the·ac­cessibility of military high explosives to terrorist organizations makes them very common constituents of homemade bombs. RDX is the most popular and powerful ofthe military explosives.

The .entire bomb site must be systematically searched with great .care given to recovering any trace of a detonating mechanism or any other•item foreign to the explosion site. Objects located at or near the origin of the explosion must be collected for laboratory examination.

Typically, in the laboratory, debris collected at explosion scenes is examined microscopically for unconsumed explosive partiCles. Recovered debris may also be thoroughly rinsed with organic solvents and analyzed by testing procedures that include color spot tests, thin.:layer chromatog­raphy, high-performanceliquid chromatography, and gas chromatography/ mass spectrometry.

Review Questions Facts and Concepts

1. What produces the violent physical disruption associated with an explosion?

2. What is the difference between deflagration and detonation?

3. What is the difference between low explosives and high explosives?

4. What are the most widely used low explosives?

5. What is a safety fuse and what is it used for?

6. What ingredients are required to create a low explosive?

7. What are the two classes of high explosives? What is the difference between the two classes?

8. What are the main ingredients in straight dynamite? What other substances also are included in modern straight dynamites and what purpose do they serve?

9. What types of explosives largely have replaced dynamite for industrial uses? What are the advantages of these types of explosives?

10. What is ANFO?

11. Name three military high explosives. Which is the most powerful and popu­lar of these explosives?

12. What is a detonator? What is the composition of most detonators?

13. What is the most obvious post-explosion characteristic of a high or contained low explosive?

14. What device is widely used to screen objects for the presence of explosive residues?

Forensic Investigation of Explosions 469

15. How are soil and other soft loose materials collected at the scene of an explo­sion best stored?

16. What is the first procedure typically used to analyze bomb-scene debris that arrives in the laboratory?

17. What does the forensic scientist do to explosive debris following microscopic examination? Why?

18. List three procedures commonly used as screening tests for explosive residues.

19. Name two confirmatory tests for the presence of intact explosives located in debris.

20. What is a taggant? What purpose do taggants serve?

Application and Critical Thinking t The following pieces of evidence were found at separate explosion sites. For

each item, indicate whether the explosion was more likely caused by low or high explosives, and explain your answer:

a. lead azide residues d. scraps of primacord b. nitrocellulose residues e. potassium chlorate residues c. ammonium nitrate residues

2. Which color test or tests would you run first on a suspect sample to test for evidence of each of the following explosives? Explain your answers.

a. tetryl c. chlorate b. TNT d. nitrocellulose

3. Criminalist Matt Weir is collecting evidence from the site of an explosion. Arriving on the scene, he immediately proceeds to look for the crater caused by the blast. After finding the crater, he picks through the debris at the site by hand, looking for evidence of detonators or foreign materials. Matt collects loose soil and debris from the immediate area, placing the smaller bits in paper folded into a druggist fold. Larger items he stores in plastic bags for transportation to the laboratory. What mistakes, if any, did Matt make in collecting and storing this evidence?

eb Resources A•Guide for Explosion and Bombing Scene Investigation (Adobe Acrobat publication from the U.S. Department of Justice outlining federal procedures for investigation of explosions) www.bombsecurity.com/downloads2/nij_181869.pdf

Arson and Explosives (Article that discusses principles of combustion, types of explosives, and investigation of explosion sites; includes brief list of links to other sites about arson and explosives) faculty.ncwc.edu/toconnor/425/4251ect07.htm

Pyrotechnics, Explosives, & Fireworks (Detailed article on the workings and types of explosives; has good material about low explosives, high explosives, and taggants) www.faqs.org/docs/air/ttpyro.html

Endnotes 1. T. Keller et al., "Application of Ion Mobility Spectrometry in Cases of Forensic

Interest," Forensic Science International, 161 (2006):130.