Destructive Nature Of Explosions Biology Essay


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The terrorist organizations and criminals usually used a destructive nature of explosions as a means of furthering their particular aims. Explosions have been used to terrorize communities, murder individuals, damage property and facilitate theft. This chapter describes what is meant by the terms explosion and explosive. It discovers the types of explosion and the role of laboratory-based techniques in the analysis of samples that are suspected either of being explosives or being contaminated with them.

1.1 Definition

An explosion is a manifestation of a sudden release of energy. It may be defined as the effect of violent produced due to the quick build-up of gas pressure at a location because of the sudden liberation of energy and, in most cases, gas at that particular location. The process that leads to agiven explosion may be chemical, mechanical, thermal, electrical or nuclear in nature. In the forensic context, explosion directly caused by chemical reactions (R.W. Jackson, M.Jackson, 2nd ed, 2004). Explosive is capable of exploding or tending to explode, which potentially violent or hazardous, dangerous and substance that decomposes rapidly under certain conditions with the production of gases, which expand by the heat of the reaction. The energy released is used in firearms, blasting, and rocket propulsion. Explosives are substances that produce a rapid, violent reaction when exposed to heat, a strong blow or a special detonator.

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Any substance that is capable of producing an explosion which restricted to those substances that can produce explosions due to chemical reactions. To trigger an explosion, this process must be initiated which requires with supply of sufficient energy, in a utilized form, to at least some part of the explosive. In order to be an explosive, a material must therefore be capable of propagating the explosive chemical process through itself from the site of initiation. There are many explosives known that consist of suitable oxidizing and reducing agents that are present in intimate combination and in appropriate proportions. This combination may be achieved by the physical mixing of materials that have oxidizing properties with those that have reducing ones. Typical oxidizing materials used for this purpose including inorganic nitrates, perchlorates and chlorates. Suitable reducing materials, which may be thought of as fuels, include carbon, sulphur, hydrocarbons, carbohydrates and finely divided metals. During the reaction, explosives give off large amounts of gases at high pressure. The powerful blast of energy released during an explosion gives explosives many commercial and military uses. Explosives let construction workers clear land away for building roads or buildings with little effort. They are used in digging mines and to loosen the flow of oil deep beneath rock in oil wells. They blow away tunnels through mountains and send rockets into space. In war, explosives are used to damage cities, destroy ships and airplanes, and kill enemy troops. As you see, explosives aren't always used as harmless substances.

Explosives may be solids, liquids, or gases. However, all explosives consist of a fuel and an oxidizer--a substance that supplies the oxygen needed to make the fuel burn. When the most powerful explosives detonate, a chemical reaction takes place very quickly (usually in less than a millionth of a second). Liquids and solids change to hot gases that expand with a large blast of heat and pressure. The higher the pressure, the more powerful the explosion is.

1.2 Significance of explosion in forensic

Establishing the nature of an explosion can be a significant challenge to the forensic investigator. The purposes of forensic to examine an explosion are for the collection and analysis of fire and explosion debris and also understand principles and chemistry of explosives. The forensic personnel also need to understand basic knowledge of chemical analysis of explosives and explosive residues and also have knowledge to improvised explosive devices. When the explosion cases occur, the forensic crews need to investigate and collect all evidences and by having a great knowledge and skills, they can examine and undergo analysis successfully. They should know how to handle the explosion material to avoid the evidence(s) contaminate or destroy. The investigation of explosion seeks their origins and causes through applications of basic method. In such cases, consultation with a forensic chemist or criminalist will provide a satisfactory explanation or the explosion. (Fischer, 7th ed) Thus, the study of explosion must be done in order to identify the source of the explosion occurred that which may associated to the particular person(s) that plan the explosive.

The forensic investigation of an explosives-related incident is two-fold; firstly is the identification of the explosives used, together with any associated hardware such as batteries, timer, container and wiring while second, if possible, to assist in identifying the involvement or not, of a person or persons in the perpetration of the crime. It is probably true to say that in any explosion, regardless of the nature of the charge or its size, there is never 100% consumption of the explosive. Some material remains, as residue or breakdown products, for recovery and detection.

2.0 Types and example of explosion

In broad terms, an explosive is a material capable of rapid conversion from either a solid or a liquid to a gas with resultant heat, pressure and loud noise. Many chemicals, alone or in combination, possess thenecessary properties foe an explosive. Explosives can be classed into two broad group; which are low explosion and high explosion (Fischer, 7th ed). The speed at which explosives decompose varies greatly from one to another and permits their classification as high and low explosives. In the low explosive, this speed is called the speed of deflagration (burning). In the high explosive, it is called the speed of detonation (Saferstein, 4th ed). During a deflagration, the speed at which the reaction front moves through the explosive is less than the speed of sound in material. In a detonation, the speed at which the reaction front moves through the explosive is greater than the speed of sound in material (R.W. Jackson, M.Jackson, 2nd ed, 2004). High explosives, in general, are detonated by shock and have much huge detonation velocities; they need not be confined to explode. High explosives consist of primary and secondary explosives; low explosives burn rather than explode. Damage by low explosives is caused by the force exerted by the rapid expansion of gases formed by burning (Fischer, 7th ed). Detonation also refers to the creation of a supersonic shock wave within the explosive charge. This shock wave causes the chemical bonds of the explosive charge to break apart, leading to the new instantaneous buildup of heat and gases (Saferstein, 8th ed).

2.1 Low explosives

The most widely used explosives in the low explosive group are black powder and smokeless powder. The popularity of these two explosives is enhanced by their accessibility to the public. Black powder is a mixture of potassium or sodium nitrate, sulfur and charcoal. There has been wide variation in the formulation of this mixture over the years. Unconfined, it merely burns; it is in fact used as a medium for carrying a flame to an explosive charge. A safety fuse usually consists of black powder wrapped in a fabric or plastic casing. When ignited, a sufficient length of fuse will burn at a rate slow enough to allow an individual adequate time to leave the site of the pending explosion. Black powder becomes explosive and lethal only when it is confined.

Actually, the only ingredients required for a low explosive are fuel and a good oxidizing agent. Thus, the oxidizing agent potassium chlorate, for example, when it is mixed with sugar, produces a popular and accessible explosive mix. When it is confined to a small container, like a pipe and ignited by the flame of a safety fuse, this mixture can explode with a force equivalent to a stick of 40 percent dynamite.

Gunpowder is an explosive material that burns rapidly to form high- pressure gas. Expansion of this gas inside the barrel of a gun can accelerate a bullet to great speed. Gunpowder is therefore used as a propellant in a variety of ammunition. It is also used in explosives for blasting operations, in fireworks, and in fuses. There are several kinds of gunpowder. The first important substance used as gunpowder in guns and cannons was black powder. Black powder consists of a mixture of saltpeter (potassium nitrate), charcoal, and sulfur. These ingredients can be mixed together in the right proportions and be used as a powder. Sometimes, graphite is added. The texture of black powder can range from fine powder to larger pellets. The basic formula for black powder has been modified for special purposes. Sulfur less gunpowder contains saltpeter and charcoal but no sulfur. It is not as powerful as regular black powder, but it corrodes the gun barrel less. Another variation is the black powder used in fireworks and blasting agents. The saltpeter is sometimes replaced by less expensive sodium nitrate.

The safest and most powerful low explosive is smokeless powder. This explosive usually consists of nitrated cotton or nitrocellulose (single-base powder) or nitroglycerin mixed with nitrocellulose (double-base powder). The powder is manufactured in a variety of grain sizes and shapes, depending on the desired application. Cordite was one of the original smokeless powders used to propel projectiles from guns. It replaced gunpowder in many cases because it burned with a lot less smoke. However, cordite damaged gun barrels much more than gunpowder did. The name cordite refers to the cordlike lengths in which it was made. Cordite is composed of 30 percent nitroglycerin, 65 percent nitrocellulose, and 5 percent petrolatum.

2.2 High Explosives

The sensitivity of a high explosive provides a convenient basis for its classification into two groups. The first group, primary explosives are ultrasensitive to heat, shock or friction and under normal conditions will detonate violently instead of burning. For this reason, they are used to detonate other explosive through a chain reaction and are often referred to as primers. Primary explosives provide the major ingredient of a blasting cap and include lead azide, lead styphnate and diazodinitrophenol. Because of their extreme sensitivity, these explosives are rarely used as the main charge of homemade bomb. Blasting caps are of two types; electric and nonelectric. They are small explosive devices, about ¼ inches in diameter and from 1-3 inches in length. The electric blasting caps have colored wires extending from them.

The second group, secondary explosives detonate by shock from a suitable primary explosive. It's known as noninitiating explosives, are relatively insensitive to heat, shock or friction and will normally burn rather than detonate if they are ignited in small quantities in the open air. This group comprises the majority of high explosives used for commercial and military blasting.

2.1.1 Nitroglycerin

Nitroglycerin, also called Nitroglycerol, is a powerful explosive. It is the principal explosive ingredient of dynamite. Pure nitroglycerin is a heavy liquid that is clear and has the consistency of motor oil. The commercial product is usually a yellowish or brownish colour. When nitroglycerin explodes, it expands to form gases that take up more than 1,000 times as much space as the liquid. That would mean that if you had 10 ml of nitroglycerin, the gases created from the explosion would be close to 10,000 ml. The explosion of nitroglycerin is about three times as powerful as that of an equal amount of gunpowder, and the explosion speed is 25 times as fast as that of gunpowder. Although its explosive capabilities are very great, it is not often used as an explosive. Doctors use nitroglycerin to treat certain heart and blood-circulation diseases.

2.1.2 RDX (Cyclonite or Hexogen)

RDX is a powerful explosive also known as cyclonite and hexogen. It is commonly used as a war explosive, being the main explosive charge in bombs. It has wide use in detonators and fuses. RDX is made by the action of nitric acid on hexamethylene-tetramine, a product of formaldehyde and ammonia. When RDX is mixed with liquid TNT, an explosive called Composition B is formed. This explosive is more powerful than TNT, and has replaced it in most artillery shells.

2.1.3 TNT (Trinitrotoluene)

TNT is short for trinitrotoluene, a powerful solid explosive. TNT is made up of the elements nitrogen, hydrogen, carbon, and oxygen. The explosive is made by nitrating the chemical compound toluene. The explosive made forms in pale yellow crystals that may darken to a darker brown colour. These crystals of TNT can be handled safely. TNT can be melted at low heat without igniting, and so can be molded to increase its usefulness. TNT is used alone and in mixtures with other explosives, such as PETN, RDX, and ammonium nitrate. It is mainly used as the explosive charge for shells and bombs.

2.1.4 PETN (Pentaerythritol Tetranitrate)

PETN is short for pentaerythritol tetranitrate, an explosive more powerful than TNT. It is used as the core of detonating caps and fuses because it is capable of exploding in small devices. The combination of PETN and TNT is called pentolite. Doctors also use PETN like they do nitroglycerin, in treating some heart disorders.

3.0 General Forensic Examination of Explosive

The criminal investigation of a bombing incident has the same objective as any other investigation; to identify the person(s) responsible and bring them before the courts. In this sense; a prosecutor will normally require the investigator to provide evidence that the person(s) charged had the motve, opportunity and means to commit the crime.

In bombing incidents, the investigation at thescene should quickly provide two of three essential pieces of information which pertain to motive, opportunity and means;

The target(s)

The victim(s)

but the third piece of information usually takes make longer:

The design of the explosive device(s)

The following outlines the main points to be considered by the first responders to the scene of an explosive.

The job of the first responders is to tend to the injured and protect the scene.advance education and training of police, fire and ambulance personnel in explosive scene protocols pay large dividends.

Jurisdiction must be established immediately-one person must assume control of the scene and the criminal investigation

Boundaries are extablished, normallu the apparent outer limit of scattered debris plus an additional distance of 20%

The scene must be declared safe by a bomb technician before the physical investigation can commerce (Hall,1991)

Structural integrity and safety hazards such as gas leaks must be assessed and dealt with by qualified personnel

Witnesses must be identified and questioned before they disappear

Investigation of the scene of an explosion aims to discover whether an explosion actually took place and, if so, whether it was an accident or a bomb. The forensic scientist will then try to find out what kind of explosion occurred, the materials involved and, in the case of a criminal act, they will work with the police to find out who was responsible. Examination of the scene and witness reports can establish whether an explosion has happened. Loud bangs, flashes, violent eruption of debris, shattering of nearby objects and formation of a crater where the event occurred are all indicative of an explosion. The investigator will look for evidence of a possible accident, such as a gas leak or creation of a cloud of flammable gas at the scene. If it looks as if a bomb caused the explosion, then the explosive device must found. This involves searching for the device itself and any detonator fragments which may be scattered among the debris. There may have been a timing device to allow the bomber time to get away, which would consist of electronic circuitry, wires, and batteries. The remains of the device will probably contain some residue from the explosive and may even bear fingerprints from the perpetrators. The construction of the device and how it was triggered may also be deduced from examination of these fragments.

The investigator will probably have to search far and wide at the scene of the explosion to recover bomb fragments. Some may be embedded in the bodies of victims, and here medical staff will need to carry out x rays to identify any evidence and, if possible, recover it for forensic investigation. A suicide bomber is, of course, an important source of such evidence. Suspect surfaces must be swabbed with various solvents to extract invisible chemical traces of explosive residue. There is nearly always a part of the bomb that did not explode and these residues can be very informative. Small items that may bear explosive residue can be placed in a beaker and agitated with a suitable solvent. The solvent has to be chosen to match the explosive-diethyl ether may be used for organic materials, while water dissolves inorganic materials such as potassium chlorate.

Once the samples are back in the laboratory, there are many sensitive analytical techniques, such as high performance liquid chromatography and thin layer chromatography, that can be used to assess the chemical nature of explosives and identify the trace evidence, comparing it with reference samples of explosives. Similar techniques can be used to sample for traces of explosives on suspects' hands and clothing. Comparison may be sufficient to link a suspect with a crime scene. The analysis of traces of explosives has to be done with great care and expertise because there is ample opportunity for cross contamination to occur. This means taking scrupulous care with the collection of the trace evidence and then using control samples throughout the analysis. If the explosive can be identified, the police investigation will look for buyers and sellers of that particular material. A wide range of techniques may be used for the analysis of samples that are suspected of being composed of, or contaminated with, explosives.

These include:

The physical testing of the explosive properties of the sample

Spot tests (i.e. chemical tests devised to produce visible changes in the presence of small amounts of specific types of chemical and that may indicate the presence of an explosive

Light and scanning electron microscopy, allowing the determination of the elemental composition of the sample

Infrared spectroscopy is a technique that can allow the detection of the presence of individual chemical species or chemical functional groups, and that provides multiple points of comparison between samples

When the evidence has been recovered from the crime scene, work begins in the lab to reconstruct the event that produced the destruction. Arson and explosion investigators analyze residues to get information about the accelerants or explosives involved in the crime. They often perform carefully planned control experiments to try to recreate the crime, especially when they need to test different hypotheses about the events.The arson and explosion investigator must take detailed notes during every step of the process. These notes are used to write a full report about the analysis and its conclusions. If the evidence from the analysis is used in a case that goes to trial, the arson and explosion investigator may be required to testify in court about the work.

Explosions often cause characteristic damage to nearby surfaces through a combination of the high temperature generated and the high pressure wave. A mottled irregular appearance, known as gas wash, results from a combination of melting and erosion of the surface material. Textiles may undergo characteristic clubbing damage as the polymer melts and then re-solidifies. On metal surfaces, microcraters may be visible on microscopic examination. Soot deposits on more distant surfaces, such as window frames, are also characteristic of an explosion.

The pattern of damage at the scene of an explosion will help the forensic scientist to determine what happened. The location and depth of any crater or the nature of structural damage such as broken windows can all help to locate the actual seat of explosion, for instance. The scene can also be very informative about the nature of the explosion too, as different combinations of explosive and explosion can give rise to characteristic types of damage. Detonation of a condensed explosive tends to produce a huge crater and very severe damage that involves pulverizing and shattering of nearby objects, even if they are made of tough materials like steel. A deflagration in a condensed explosive produces intense heat and could bend or melt objects rather than cutting them. Detonation is rare with dispersed explosives, but deflagration gives a pattern in which most of the damage may occur some way from the explosion itself owing to a pushing out effect. In one example, a natural gas explosion caused only superficial burns to two people in the basement underneath the room where it occurred, yet the incident was violent enough to blow furniture out of the building.

Some explosions are of a mixed type. Petrol (gasoline) bombs are often used by terrorists and typically involve using a small charge of high explosive to disperse and ignite petrol, which is a flammable liquid. This event involves detonation of a high explosive and deflagration of a dispersed explosive. The detonation will produce damage close to the point where the bomb was set off, while the deflagration will produce damage further away.

4.0 Analysis of Smokeless Powder

Smokeless powder has the highest evidentiary potential of all explosive materials encountered by the forensic chemist. Brand identification can generate investigate leads if the source of the powder can be traced. Powerful associative evidence can be generated by the comparison of powder from a device to powder in a suspect's possession. The development of smokeless powder from a device to powder in a suspect's possession.

All smokeless powders contain nitrocellulose. They are divided into 3 classes by the chemical composition of their primary energetic ingredients:

Single base powder (NC)

Double base powder (NC, NG)

Triple base powder (NC, NG and nitroguanidine)

Smokeless powders are used as gun propellants. Triple base powders are used in large caliber munitions and are rarely if ever encounterd in IEDs.

4.1 Single Base and Double Base Smokeless Powder

Commercial smokeless powder for rifle, pistol and shotgun propellant use are widely available in bulk form ( at least in North America) for use in hand loading. An excellent description of many available, these powders frequently are encountered in IEDs, especially pipe noted above, single base powder contains only NC as an energetic material whereas double base powder contains NC and NG. Also both classes of powder contain chemical additives. Identification of these can greatly assist in individualizing the powder.

4.1.1 Additives

In addition to primary energetic ingredients, smokeless powders contain as additive package of chemicals which serve various purposes.

Stabilizer: prevent decomposition of nitrocellulose by scavenging the nitric and nitrous acids which are produced during nitrocellulose decomposition and which catalyse further decomposition if not removed. The most common are diphenylamine (DPA) and methyl and ethyl "centralite" ( N,N'-dimethyl diphenylurea respectively)

Gelatinizing agents/plastizers : reduce the amount of volatile solvents necessary to colloid the nitrocellulose, or in the case of some double base propellants allow manufacture with no volatile solvents at all. These include nitroglycerin, phthalate plasticizer, dinitrotoluene and ethyl centralite

Surface Coatings : modify burning rate, affect flow or electric properties (carbon, black and graphite) or serve as flash suppressants (zinc powder, potassium sulphate)

4.1.2 Analysis

The analysis of smokeless powder usually has one or more of the following goals:

Defining the material as an explosive substance;

Determining the manufacturer or source;

Comparison of one powder to another

Identifying the material as an explosive substance involve identifying NC (and NG if double base). The other goals require identification of additives. Effective methods for these purposes are described below. Nitrocellulose (NC)

All smokeless powder contain NC. The best method for identifying NV is to produce the IR spectrum of a film pressed in a diamond cell or cast from acetone, tetrahydrofuran, methanol or ethyl acetate onto a diamond or onto a NaCl or KBr disc (Kee et al. 1990). To obtain a pure spectrum, the film should be extracted with methylene chloride or chloroform to remove additives prior to IR analysis. The technique is non-destructive and NC can be recovered for further analysis.

TLC is a useful complementary technique. In many commonly used TLC solvent systems NC has an Rf of zero, but Douse (1982) reported that when developed with acetone: methanol 3:2 on a silica gel plate, NC has an Rf of 0.64.

Interpretation of the significance of finding traces of NC by solvent extraction of debris, clothing and skin (no unracted particles observed) must be undertaken with caution since NC can be a component of paint, nail polish, varnish and collodion. The same caution applies to diphenylamine a common additive, which occurs widely in the environment. Distinguish between the different kinds of nitrocellulose is difficult. Nitroglycerin (NG)

If unreacted smokeless powder is removed from an unexploded device and it is only necessary to determine if it is an explosive material, this can be done simply by analyzing a sample by IR to identify the nitrate ester content and then analyzing an acetone extract by TLC to determine if it is single or double base (Beveridge et al., 1975). The cited publication used a solvent system of benzene: hexane (1:1). In this system, on heat-activated silica gel plates, NC has an Rf of zero and NG an Rf of approximately 0.3. There are many other equally effective solvent systems. NG can also be detected by many instrumental techniques including GC/MS, GC/TEA and others. The same preocedure may be applied to unreacted particles recovered after an explosion.

TLC Archer (1975) published a system of six solvent systems designed to identify 21 smokeless powder additives including diphenylamine and derivatives. Nitrotoluenes and substituted ureas (centralites). He used heat-activated silica gel plates which were developed with six solvent systems,, five of which included benzene. Benzene is now contraindicated for health reasons and toluene has been proposed as a substitute. On this basis, the systems become: (A) toluene; (B) toluene : light petroleum (bp 40-60) : ethyl acetate 12:12;1; (c) toluene: petroleum (bp 40-60) ; (D) toluene: chloroform 1:1; (E) choloform; (F) toluene:methanol 4:1. He visualized the plates by use of UV radiation and four spray reagents: vanillin, tetramethylammonium hydroxide, Griess reagent and potassium dichromate.

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