| Friday, June 29, 2007 marked another day in | | | | dependent upon their sensitivity to heat, friction, or |
| London's history in which a terror scare rocked the | | | | mechanical shock. |
| people of this city. Fortunately, nobody was hurt | | | | - Initiating explosives are highly sensitive to these |
| unlike the last bombing that struck a London public | | | | effects. Because of their instability, home-made |
| transport system nearly two years ago next week. | | | | bombs rarely use initiating explosives. These |
| Two car bombs were discovered and quickly | | | | explosives are usually found in primers and blasting |
| defused by a Scotland Yard bomb squad. Now the | | | | caps, where they initiate other more stable |
| hunt goes on to find the perpetrators who could | | | | noninitiating explosive reactants. Mercury fulminate |
| have caused such mass destruction of innocent lives. | | | | and lead azide are widely used in this manner. |
| If these car bombs did explode, how do forensic | | | | - Noninitiating explosives are more stable and |
| criminal investigators go about evaluating this | | | | commonly used in military and commercial applications. |
| particular crime scene? In this article, we will attempt | | | | Examples of these explosives include dynamite, |
| to explain how the investigators evaluate explosive | | | | trinitrotoluene (TNT), pentaerythritrol tetranitrate |
| situations, how they define explosives, and how they | | | | (RDX), and cyclotrimethylenetrinitramine (PETN). |
| go about investigating a bomb scene. | | | | ANFO, an easily made explosive material, is a mixture |
| Explosions and fires are similar chemical reactions that | | | | of ammonium nitrate and fuel oil. |
| take place since both result from the consumption of | | | | Ammonium nitrate is an oxidant loaded with oxygen |
| fuel and oxygen. The only difference between the | | | | and can be found in fertilizers. Bombs made from this |
| two is that an explosion reaction occurs faster than a | | | | material were used in the Oklahoma City and 1993 |
| fire reaction. Explosion reactions use up their fuel such | | | | World Trade Center bombings. |
| as gasoline or gunpowder almost instantaneously | | | | Investigating a Bomb Scene |
| partly because the materials are confined to a small | | | | Looking through the scene of an explosion requires |
| space. Fire reactions, on the other hand, consume | | | | the same attention to detail as does a search of a |
| their fuel such as wood, trees, or paper more slowly | | | | fire scene. Searching for remnants of an explosive |
| than explosion reactions. If you ignited these | | | | device such as the igniter and timer may be |
| materials in an open space, the materials simply burn. | | | | important in determining the type of explosive used |
| In contrast, if you tightly pack these same materials | | | | and the persons responsible for this crime. |
| into a container, it explodes when you light it up. | | | | Furthermore, forensic criminal investigators focus their |
| Explosions pose problems for investigators. The | | | | searches on gathering debris to test for unexploded |
| explosive device and any surrounding structures are | | | | residue, which is almost always present. |
| heavily damaged if not entirely obliterated. Unless a | | | | Microscopic examination of the debris may unveil |
| secondary fire occurs, investigators can usually | | | | black powder, gun powder, or both of which are |
| ascertain the point of origin with no problem. Finding | | | | easily recognizable by the color and conformation of |
| fragments of the device, timers, or igniters is another | | | | their particles. After conducting a microscopic |
| story. | | | | inspection of the debris, the lab technician rinses the |
| Explosives are categorized as either high or low | | | | debris with a solvent, usually acetone, and then |
| according to the speed of their resulting shock wave. | | | | analyzes the resulting solution, using various scientific |
| Low explosives usually move at rates of up to 1,000 | | | | laboratory techniques such as thin-layer (TLC) or gas |
| m/s, and high explosives may reach speeds up to | | | | chromatography (GC) and mass and infrared |
| 8,500 m/s. | | | | spectroscopy. Determining the identity of the |
| Black powder and smokeless gunpowder are the | | | | explosive is made through a combination of these |
| most readily available and commonly used low | | | | techniques. |
| explosives. A mixture of table sugar and potassium | | | | After determining the nature of the explosive used, |
| chlorate makes another easy explosive. Bombers do | | | | criminal investigators then target their investigation on |
| not need to be complex. | | | | the seller and buyer of that explosive. |
| High explosives can be divided into two categories all | | | | |