1. Chapter 15
Explosives

2. Objectives Students should gain an understanding of:
The classification of explosives
The composition of commercial explosives such as dynamite and ammonium nitrate/fuel oil (ANFO)
The composition of military explosives
How improvised explosive devices (IEDs) are made
Field tests for explosive residue
Confirmatory laboratory tests for explosive residue
The use of taggants to identify the manufacturer of an explosive

3. Introduction Explosives are attractive weapons:
Can be made at home
Bring considerable attention to bombers’ issue
Bombings may be political in nature, grudges between motorcycle gang members, or the work of petty criminals.
Explosives can be sophisticated in nature or very crude pipe bombs.

4. Explosions
Explosion: a release of mechanical or chemical energy in a violent manner
Generates heat and the release of gas
Can create a rapid chemical reaction that produces large quantities of gas
Explosive: a substance capable of producing an explosion
Usually held in a metal container
May include nails or glass intended to cause more harm

5. Types of Explosives (1 of 6)
Deflagration
A chemical explosion in which the reaction moves through the explosive at less than the speed of sound
Low explosives = deflagration

6. Types of Explosives (2 of 6)
Detonation
A chemical explosion in which the reaction front moves through the explosive at greater than the speed of sound
High explosives = detonation

7. Types of Explosives (3 of 6)
Low explosives (black powder and smokeless powder)
Conversion of solid reactants into gaseous products provides pressure for explosion
Combustion requires two components: a fuel and an oxidant
Production of nitrogen and carbon dioxide is highly exothermic, which is why nitrogen is a main constituent of explosives

8. Types of Explosives (4 of 6)
Low explosives burn (rather than explode) if not confined in a container
Fuse for a low explosive: black powder wrapped around a fabric such as cotton
Condensed explosives: solid or liquid
Dispersed explosives: gas or aerosol

9. Types of Explosives (5 of 6)
Pipe bomb
Most common illegal explosive device in the United States
Usually contains black or smokeless powder or an improvised explosive mixture
Improvised explosive device (IED)
Any explosive material confined in a closed pipe that is fitted with a detonating device

10. Types of Explosives (6 of 6)
High explosives
Primary high explosives: extremely sensitive to shock and heat; detonate powerfully
Secondary high explosives: more stable
Primers: used to set off a bomb that contains a charge of secondary explosives

11. Commercial Explosives (1 of 4)
Nitroglycerine (NG)
First high explosive that was widely used in commercial application
Oily liquid that is extremely sensitive to shock

12. Commercial Explosives (2 of 4)
Dynamite
NG’s sensitivity is greatly reduced when it is absorbed into an inert material
The resulting product—dynamite—can be shipped and handled without danger
Dynamite’s invention made large-scale blasting possible

13. Commercial Explosives (3 of 4)
Dynamite
Original formula’s ignition was unreliable in cold climates
Problem was solved by adding ethylene glycol dinitrate to reduce the freezing point
Most common dynamite composition in North America is 80/20 mixture of EGDN and NG

14. Commercial Explosives (4 of 4)
Ammonium nitrate/fuel oil (ANFO)
AN fertilizer is widely used by farmers.
AN mixed with a source of carbon or fuel oil makes a cheap explosive.
The most common explosive in the world today is a 94% AN and 6% FO mixture.
ANFO requires a primer charge to initiate a blast, so it is classified as a blasting agent.
Large amounts have been used in terrorist bombings.

15. Military Explosives (1 of 7)
Military explosives are manufactured for specific purposes
Such explosives must be produced from cheap raw materials that are not strategic and are available in great quantity
Operations to manufacture them must be simple, cheap, and safe
Density of explosives needs to be as high as possible

16. Military Explosives (2 of 7)
TNT (2,4,5-trinitrotoluene)
Was dominant military explosive during World War I
Was conserved during World War II by mixing it with ammonium nitrate

17. Military Explosives (3 of 7)
Characteristics of TNT
Has a low melting point
Is not sensitive to shock
Will not spontaneously explode
Can include a detonator if the goal is to produce a pressure wave
Can quickly change from a solid to hot, expanding gas

18. Military Explosives (4 of 7)
RDX (cyclotrimethylenenitramine)
Remains stable in storage and at room temperature
Is the most powerful and brisant of the military high explosives
Reaches maximum pressure so rapidly that a shock wave forms
Reacts concentrated nitric acid with hexamine
Must be used in conjunction with a detonator to produce an explosion

19. Military Explosives (5 of 7)
C-4
A popular explosive choice among terrorists
Military plastic explosive that is about 90% RDX; remainder is a plastic binder material and oil

20. Military Explosives (6 of 7)
PBX (plastic bonded explosive)
Plastic binder coats the explosive material, making it safer to handle
Plastic binder makes the explosive material easy to mold into different shapes

21. Military Explosives (7 of 7)
HMX (high-melting-point explosive)
Also known as octogen
About 30% more powerful than TNT
Powerful, yet shock-sensitive, nitroamine-based high explosive
Chemically related to RDX

22. Improvised Explosives (1 of 4)
1990–1994: 64% of all bombings reported in the United States involved low explosives
Components of a low-explosive IED:
Container to confine the explosive
Fuse or primer to detonate it

23. Improvised Explosives (2 of 4)
Types of low-explosive IEDs
Commercially available products modified to act as explosives
Combinations of chemicals

24. Improvised Explosives (3 of 4)
Composition of low-explosive IEDs
Low-explosive IEDs: contents of road flares, match heads, powder from shotgun shells, or chemicals from fireworks
Pipe bombs: (1) potassium nitrate with sugar and aluminum; (2) sulfur/charcoal, potassium chlorate, and sugar; or (3) potassium perchlorate with sugar and aluminum
MacGyver bomb: toilet bowl cleaner, aluminum foil in a 2-L plastic soda bottle

25. Improvised Explosives (4 of 4)
High-explosive IEDs: TATP
New terrorist explosive used in the Middle East
More powerful than military-explosive analogs
Extremely sensitive to impact, temperature change, and friction
Similar operation to decomposition of an azide, which is used in automobile airbags to produce nitrogen gas

26. Initiators (1 of 5)
Initiator: a device used to start a detonation or deflagration
Most common IED in the United States is a pipe bomb filled with low explosive charge
Most popular initiator for those bombs are the safety fuse and the electric match
Detonator (blasting cap): a device used to set off a high explosive

27. Initiators (2 of 5)
Safety fuse: when ignited at one end, is intended to burn uniformly and to transmit the flame from one point of ignition to the IED
Application: fits into the opening at the end of a pyrotechnic or fuse detonator, where it triggers a fuse detonator
Fuse detonator: metal shell that is loaded with two or three types of explosive powder

28. Initiators (3 of 5)
Electric match: triggers an IED when it is set off by an electrical current
The resistance wire is coated with a pyrotechnic composition that ignites when the wire is heated.
Bombers typically attach the electric match to a timer that is rigged to close a switch in an electrical circuit at a specific time.

29. Initiators (4 of 5) Detonators
Military mines use mechanical detonators, which are activated when someone steps or drives on them.
Commercial and military high explosives use electrical detonators.

30. Initiators (5 of 5) Electrical detonators
Insulated wires are attached to a high-resistance bridge wire.
Pyrophoric material is pressed into place above the match head.
When electric current from a blasting machine passes through the wires, the bridge wire heats quickly, igniting the pyrophoric material, which then ignites the explosive.

31. Collection of Explosive-Related Evidence (1 of 4)
Precautions
Personnel involved in bomb scene or bomb threat searches should look for and report suspicious objects.
Post-blast, bomb disposal experts should first search for a secondary bomb.
Only then should investigators attempt to determine the point of detonation and type of blast effects.

32. Collection of Explosive-Related Evidence (2 of 4)
Searching the site
Begin the search for bomb evidence at the site of the crater and then proceed outward.
Sift, sort, and collect samples.
Use wire mesh screens to sort through the rubble.
Have explosives detection canines search the scene.

33. Collection of Explosive-Related Evidence (3 of 4)
Send all materials to the lab in sealed, labeled containers
Soil and loose debris: metal containers or plastic bags
Sharp objects: metal containers

34. Collection of Explosive-Related Evidence (4 of 4)
Date/shift code
Manufacturers must identify explosives with a date, shift, and place of manufacture
ATF can use the date/shift code to trace commercial and military explosives recovered by law enforcement

35. Field Tests for Explosive Residue
Ion mobility spectrometer
Presumptive test
Can detect a wide range of explosives
Portable hydrocarbon detector
Can detect residue on objects or people
Specially trained dogs
Chemical reagents

36. Laboratory Analysis of Explosive and Explosive Residues (1 of 6)
Examine evidence microscopically
Search for fingerprints, tool marks, and other identifying marks
Run chemical tests on high explosives
Rinse recovered materials with acetone (dissolves many organic materials)

37. Laboratory Analysis of Explosive and Explosive Residues (2 of 6)
Thin-layer chromatography: a presumptive chemical test used to screen for the presence of an explosive
TLC separates compounds based on their size, shape, solubility in solvent, and interaction with the thin-layer plate.
A compound will travel a fixed distance relative to the distance traveled by the solvent front.
Multiple samples and standards can be spotted on the same TLC plate.

38. Laboratory Analysis of Explosive and Explosive Residues (3 of 6)
Gas chromatography: a confirmatory test for organic explosive residue
Each component of the residue has a unique retention time.
GC uses a thermal energy analyzer to detect volatile organic compounds.
Once the flow rate and temperature of the TEA furnace are set, a reference sample is injected and the GC determines its composition.

39. Laboratory Analysis of Explosive and Explosive Residues (4 of 6)
Infrared tests
Each explosive gives a characteristic IR spectrum.
The spectrum of the residue at a bomb scene can be compared to the standard IR spectrum of each explosive.
The investigator may need to chemically separate mixtures of explosive materials before performing IR analysis.

40. Laboratory Analysis of Explosive and Explosive Residues (5 of 6)
Analysis of inorganic explosive residues
Analysis of inorganic cations and anions in the debris may help investigators determine the composition of the explosive.
When ammonium nitrate or potassium perchlorate is suspected, the residue can be washed with water.
If spot tests indicate the presence of an inorganic substance, confirmatory ion chromatography should be performed.

41. Laboratory Analysis of Explosive and Explosive Residues (6 of 6)
Ion chromatography
Components of IC instrument: solvent reservoir, solvent pump, sample injector, separation column (containing an ion-exchange resin), detector, date system
Instrument must be set to handle anion separation.
Separate IC analyses are performed from cations and anions.

42. Taggants (1 of 2)
Identifiers may be put into batches of explosives that can help track down the manufacturer and purchaser of the material.
Types of taggants:
Tiny multicolored chips of plastic that could be recovered from crime scene
Addition of isotopes to compounds

43. Taggants (2 of 2)
Isotopes have not been shown to survive a severe blast or be recoverable using current evidence collection standards.
Less than 2% of criminal bombings involve commercial explosives, so the vast majority of bomb scene investigations would not be facilitated by the use of taggants.