1. Explosives and Explosions

2. I. Characteristics of Explosives and Explosions
An explosion is a very rapid chemical reaction that produces heat and gaseous products
Explosions produce a large amount of heat (an exothermic reaction) in a very short time period
Molecular fragmentation converts the solid explosive material into an enormous number of gas molecules which will occupy a much greater volume, further enhanced by the very high temperature of the explosion

3. I. Characteristics of Explosives and Explosions
The rapidly expanding gases compress the air creating a physical force known as a shock wave
It is the shock wave that is responsible for much of the damage associated with an explosion

4. II. The Three Major Classes of Explosives
1. Low Explosives:
Low explosives are materials that burn rapidly and will only explode if contained
Examples include smokeless powder and fireworks (pyrothechnics)
Smokeless powders consist of nitrocellulose and black powder

5. II. The Three Major Classes of Explosives
2. Primary High Explosives:
Are used as primers or detonators
Are sensitive to shock, heat, and electrical spark
Examples include nitroglycerine, and mercury fulminate & lead styphnate which are used as primers in cartridges and blasting caps

6. II. The Three Major Classes of Explosives
3. Secondary High Explosives:
High explosives do not have to be contained to explode
Are relatively stable and safe to handle
Initiation requires an electrical spark, fuse, intense heat, or sharp blow
Examples include dynamite, TNT, PETN, RDX, & ammonium nitrate

7. III. The Explosive Train or Device
The explosive train is the combination of components needed for a successful explosion (i.e. a bomb)
An explosive device or train has three primary components:
The igniter starts the event (e.g. a spark)
The primer or detonator contains a primary high explosive (e.g. blasting cap)
The main charge is a low explosive or secondary high explosive (e.g. dynamite)

8. IV. The Role of the Scene Investigator
The investigator must sort through all of the debris to find any portion of the explosive device and residue
The debris is examined and any large pieces that do not appear to have been near the center of the explosion are removed
The remaining debris is sifted through screens and examined for portions of the explosive device or items that show evidence of being close to the seat of the explosion
Promising pieces are forwarded to the lab

9. V. Laboratory Analysis of Explosives and Explosive Residues
1. Examination of an Unexploded Device:
The device must first be rendered safe
A detailed description is then made of each component and how they are connected to form the explosive train
The chemical nature of the explosive ingredients is then determined, as an investigative lead and possible identification of the manufacturer