OFFICIAL Arson/Explosives (right answers)

3. Molecules must absorb energy to _______________, and they liberate energy when ________________.

-break apart their chemical bonds -their bonds are reformed

17. What is an insulator? Give an example of a good insulator.

-materials that are poor conductors of heat example: wood

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

A safety fuse consists of black powder wrapped in a fabric or plastic casing. It is used to carry a flame at a uniform rate to an explosive charge.

9. What is the primary focus of a fire-scene search and why? What evidence at a fire site may indicate the possibility of arson?

A search of the fire scene must focus on finding The fires origin, for this area will prove most productive in any search for an accelerant or ignition device. Telltale signs of arson include evidence of separate and unconnected fires; use of streamers such as a trail of gasoline or paper to spread the fire from one area to another; the presence of containers capable of holding an accelerant; finding a potential ignition device; and an irregular shaped pattern on the floor or on the ground caused by pouring and accelerant onto the surface.

22. Why should fire evidence be packaged in airtight containers?

Airtight containers so possible accelerant residues are not lost through evaporation.

8. What role does ammonium nitrate play in water gels, emulsions, and ANFO explosives? In what commercial form can ammonium nitrate be readily obtained?

Ammonium nitrate is an oxidizing agent- it supplies the oxygen needed to detonate the explosive. Ammonium nitrate is readily available in a commercial form as fertilizer.

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

Ammonium nitrate-based explosives- they are cheap and very stable.

What is ANFO?

An explosive consisting of ammonium nitrate soaked in fuel oil.

2. What is an oxidizing agent? Why is an oxidizing agent important to an explosion?

An oxidizing agent is a chemical that supplies oxygen to a reaction. Oxidizing agents are important to explosions because detonation occurs so rapidly that oxygen in the air cannot participate in the reaction; thus, many explosives must have their own source of oxygen.

12. Define and give two examples of glowing combustion.

Glowing combustion is combustion on the surface of solid fuel in the absence of heat high enough to pyrolyze the fuel. Examples- a burning cigarette and red-hot charcoals.

24. What is headspace? How is it recovered?

Headspace is vapor containing volatile residues recovered from debris at a fire scene. It is recovered by heating the airtight container containing the debris, which drives off any volatile residue present and traps it in the container's enclosed airspace. The headspace is then removed with a syringe.

2. The quantity of heat from a chemical reaction comes from a. the breaking and formation of chemical bonds. b. the presence of oxygen in the reaction c. the emission of radiation. d. the composition of the fuel-air mix.

a

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 b. TNT c. chlorate d. nitrocellulose

a. Alcoholic KOH. Tetryl is the only explosive that produces a red-violet color in response to this test. b. Alcoholic KOH. TNT produces a distinctive red color in response the the alcoholic KOH test. c. Diphenylamine produces a blue color. No color is produced in response to the Greiss test and to the alcoholic KOH test. d. Diphenylamine. Nitrocellulose produces a distinctive blue-black color in response to this test.

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

a. High explosives. Lead azide is a common component of blasting caps, which are used to detonate high explosives. b. Low explosives. Nitrocellulose is an ingredient in smokeless powder, a common low explosive. c. High explosives. Ammonium nitrate is the main ingredient in a number of high explosives that have replaced dynamite for industrial uses. d. High explosives. Primacord is used as a detonator to ignite several high-explosive charges simultaneously. e. Low explosives. Potassium chlorate mixed with sugar is a popular low explosive.

1. Indicate which method of heat transfer is most likely to be responsible for each of the following: a. ignition of papers in the room where a fire starts b. ignition of electrical wiring in a room adjoining the fire's point of origin. c. ignition of roof timbers d. ignition of a neighboring house

a. radiation b. conduction c. convection d. radiation

3. What mistakes if any, did Mick make in collecting evidence? (passage on packet)

1) He should've used separate containers for each location where debris was collected. 2) Debris should've come from the point of origin of the fire, not from the surrounding rooms. 3) He shouldn't have places the timbers in plastic bags, vapors will be depleted. 4) He should've collected the suspect's clothes to undergo laboratory analysis for the presence of accelerant residues.

What mistakes, if any, did Matt make in collecting and storing this evidence? (passage on packet)

1) Matt should've put on disposable gloves, shoe covers, and overalls before beginning his search. 2) He should've used wire mesh screen to sift through the debris instead of picking through it by hand. 3) All explosive evidence should be stored in metal airtight containers, not plastic or paper bags. 4) Matt should've collected evidence not only from the immediate area of the blast, but also materials blown away from the blast's origin.

14. What three requirements must be satisfied to initiate the sustain of combustion?

1) a fuel must be present 2)oxygen must be available in sufficient quantity 3)heat must be applied to initiate combustion and sufficient heat must be generated to sustain the reaction

19. Name three reasons why arson investigators must work quickly to collect evidence at a fire scene.

1) any accelerant residues may evaporate within a few days or even hours 2) safety and health conditions may require that cleanup and salvage operations begin asap 3) accelerants in soil and vegetation can be rapidly degraded by bacterial action

1. List three factors that make investigating arson particularly difficult for forensic scientists.

1) perpetrator has thoroughly planned act 2) perpetrator has left the scene long before an investigation is launched 3) extensive destruction that frequently dominates the crime scene makes it more difficult to obtain proof of the commission of the offense

18. List three common signs of arson at a fire scene.

1) presence of accelerants 2) discovery of an ignition device 3) irregularly shaped burn patterns on the floor or ground, streamers, and separate and unconnected fires

7. Name two factors that influence the speed of reaction of a fire?

1) the physical state of the fuel 2) temperature

7. What is a detonator? What is the most common form of detonator?

A detonator is a device used to initiate an explosion using high explosives. The most common type of detonator is a blasting cap.

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

A device used to create an explosion needed to ignite a high explosive. In most cases, detonators are blasting caps composed of copper or aluminum cases containing lead azide.

25. What is the main advantage of vapor concentration over the headspace technique?

A forensic analyst can increase the sensitivity of accelerant detection at least a hundredfold over the conventional headspace technique.

9. In what liquid does a forensic scientist rinse debris recovered from an explosion site and why?

A forensic scientist rinses debris from an explosion site in acetone because most explosives are highly soluble in acetone. This allows the scientist to quickly remove any traces of explosive from the debris so they can be isolated and identified.

6. What are the primary explosives and what are they used for?

A primary explosive is a high explosive that is easily detonated by heat or shock. They are used to detonate the most commonly used high explosives, which are known as secondary explosives. Primary explosives are necessary because secondary explosives are relatively insensitive to heat shock or friction and usually burn rather then detonate if ignited in small quantities in the open air.

7. What are oxidizing agents and why are they used in explosives?

An oxidizing agent is a substance that supplies oxygen to a chemical reaction. An explosion occurs so rapidly that oxygen in the air cannot participate in the reaction. For this reason, many explosives must have their own source of oxygen in order to produce the chemical reaction necessary to create an explosion.

5. Why does black powder not explode unless it is ignited in a confined area? What practical application besides explosives does this make black powder suitable for?

Black powder does not explode when unconfined because it decomposes to slowly. This makes black powder suitable for use in safety fuses, in which it carries a flame to an explosive charge.

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

Metal containers

What is the difference between deflagration and detonation?

Deflagration is characterized by very rapid oxidation that produces heat, light, and a subsonic pressure wave. Detonation is characterized by extremely rapid oxidation that produces a supersonic shockwave.

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

Everything is first examined microscopically to detect particles of unconsumed explosive.

5. How does an exothermic reaction differ from an endothermic reaction?

Exothermic: heat energy is liberated (freed) Endothermic: heat energy is absorbed from the surroundings

5. What physical state must fuel be in to produce a flame? Why can it produce a flame only in this state?

Fuel must be in a gaseous state to produce a flame, because only in the gaseous can its molecules collide frequently enough to support a flaming fire.

11. How does the fuel-air mix affect combustion?

If the fuel concentration in the fuel-air mix is too low (lean) or too great (rich), combustion is too late.

2. What happens to the atoms of a molecule that undergoes a chemical reaction? How is energy consumed in a chemical reaction? How is energy released in a chemical reaction?

In a chemical reaction, the atoms of a molecule are rearranged to form new substances or products. Energy is consumed in a chemical reaction when the bonds holding the atoms of the original molecules together are broken. Energy is released when the bonds between atoms reform to create new products as a result of the reaction

13. Describe the headspace technique for recovering accelerant residues. What instrument is most often used to detect and characterize recovered flammable residues?

In the headspace technique, an airtight container holding debris from the fire scene is heated, vaporizing any volatile residue present in the debris and trapping the vapor in the containers enclosed air space. The vapor, or headspace, is removed with a syringe. A gas chromatograph is usually used to detect and characterize residues in the vapor.

12. Why might an investigator conduct laboratory tests on unburned control material collected from a fire scene?

Laboratory tests may be made on unburned control material to analyze the breakdown products caused by the materials exposure to intense heat during the fire. Because common material such as plastic, floor tiles, carpet, linoleum, and adhesives can produce volatile hydrocarbons when they are burned, these breakdown products might be mistaken for an accelerant

What is the difference between low explosives and high explosives?

Low explosives detonate relatively slowly (less than 1,000 meters per second), while high explosives detonate very rapidly (from 1,000 to 8,500 meters per second).

8. Why is it important that the arson investigator begin examining a fire scene for signs of arson as soon as the fire has been extinguished?

Most arsons are started with petroleum based accelerants that may evaporate within a matter of days or even hours. Immediate investigation may also be necessary to preserve evidence from intentional or accidental destruction. Safety and health conditions may necessitate that cleanup and salvage operations begin as quickly as possible. Once cleanup efforts begin, it is impossible to conduct a meaningful investigation of a fire scene.

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

Nitroglycerine and pulp, modern straight dynamites also include sodium nitrate (which furnishes oxygen for complete combustion) and a small percentage of a stabilizer, such as calcium carbonate.

8. In what physical state must a fuel exist in order to produce combustion when it reacts with oxygen? Why must it be in this state?

Only when it is in a gaseous state, for only in this state molecules can collide frequently enough to support a flaming fire.

1. What is oxidation?

Oxidation is the combination of oxygen with other substances to produce new substances.

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

Primary and secondary explosives: primary explosives are ultra sensitive to heat, shock, or friction, and under normal conditions detonate violently instead of burning. Secondary explosives are relatively insensitive to heat, shock, or friction, and normally burn rather than detonate when ignited in small quantities in open air, also are usually detonated by primary explosives.

10. What is pyrolysis? How does pyrolysis produce fire?

Pyrolysis is the chemical breakdown of solid organic matter by heat. The gaseous products of pyrolysis combine with oxygen to produce a fire.

6. Define and describe the process of pyrolysis.

Pyrolysis is the decomposition of organic matter by heat. In pyrolysis, heat causes solid organic matter to decay. This generates gaseous products that can combine with oxygen to produce a fire. The heat from the fire pyrolyzes more solid fuel into volatile gases, which sustains the fire.

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

RDX, TNT, and PETN. RDX is the most powerful and popular military explosive.

13. Define spontaneous combustion and give two examples of conditions under which it may occur.

Spontaneous combustion is fire caused be a natural heat-producing process in the presence of sufficient air and fuel. Examples- hay stored in an improperly ventilated barn (could catch fire) -improperly ventilated containers containing rags soaked with highly unsaturated oils.

21. What are streamers? What does evidence of their presence at a fire scene suggest?

Streamers are trails of flammable material (gasoline or paper) spreading outward from a fire's point of origin in order to cause the fire to move rapidly from one room to another. Suggests likelihood of arson

11. What are taggants and how are they used to identify explosives?

Taggants are tiny color-coded chips added to commercial explosives during the manufacturing process. Some of these chips would be expected to survive an explosion and be recovered at explosion scenes. The taggants in an explosive are arranged in a color sequence that indicates where are the explosive was made and when it was produced, which means the explosive can be traced through its distribution chain to its final legal possessor.

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

The debris is thoroughly rinsed with acetone because the high solubility of most explosives in acetone ensures their quick removal from the debris.

3. What is the energy barrier and how does it relate to the concept of ignition of temperature?

The energy barrier is the minimum amount of energy required to initiate a chemical reaction. Ignition temperature is the minimum temperature at which a fuel spontaneously ignites. Thus, the energy barrier for any fuel is directly related to its ignition temperature.

4. How does the speed of an oxidation reaction affect its ability to produce a flame? What factors influence the speed of the reaction?

The faster an oxidation reaction takes place, the greater the likelihood that it will produce a flame. Factors that influence the speed of the reaction include the physical state of the fuel and the temperature.

10. Where will an investigator usually locate the probable point of origin of a fire? What factors can cause a fire to deviate from normal behavior?

The probable origin of a fire will most likely be located closest to the lowest point that shows the most intense characteristics of burning. Factors that can cause a fire to deviate from normal behavior include prevailing drafts and winds; secondary fires due to collapsing floors and roofs; the physical arrangement of the burning structure; stairways and elevator shaft; holes in the floor, wall or roof; and the effects of the firefighters and suppressing the fire.

4. What is combustion? Why is rusting not accompanied by combustion?

The rapid combination of oxygen with another substance, accompanied by the production of noticeable heat and light. Rusting is not accompanied by combustion because iron combines with oxygen too slowly to permit combustion

3. What characteristic of an explosive determines whether it is classified as a low explosive or a high explosive? How is this reflected in the type of pressure wave produced by the explosive?

The speed at which an explosive decomposes determines its classification as a low or high explosive. Low explosives produce a subsonic pressure wave, while high explosives produce a supersonic pressure wave..

1. What produces the violent physical disruption of the surrounding environment released in an explosion? Explain how this creates shrapnel when a bomb explodes.

The sudden build up of expanding gas pressure at the origin of an explosion produces the violent physical disruption of the surrounding environment. In a bomb, the extremely high pressure caused by the expanding gases pushes on the walls of the bomb, stretching and finally shattering them. The pieces of the walls are shattered and thrown out word in all directions by the force of the explosion, creating shrapnel.

9. How high must the temperature of a liquid fuel be before the fuel will burn? What is the term for the lowest temperature at which this occurs?

The temperature must be high enough to vaporize the fuel. The flash point is the lowest temperature at which a liquid gives off sufficient vapor to form a mixture with air that will support combustion.

What produces the violent physical disruption associated with an explosion?

The violent physical disruption associated with an explosion is caused by the sudden buildup of expanding gas pressure at the origin of the explosion.

23. What instrument do most criminalists consider the most sensitive and reliable for detecting and characterizing flammable residues?

They consider the gas chromatograph the most sensible and reliable.

What is a taggant? What purpose do taggants serve?

Tiny color-coded chips the size of sand that are added to commercial explosives during their manufacture. The taggant chip is arranged in a color sequence that indicates where the explosive was made and when it was produced. They allow an explosive to be traced through its distribution chain to its final legal possessor.

4. Name two types of low explosives and list the ingredients of each.

Two types of low explosives are black powder and smokeless powder. The ingredients in black powder include potassium nitrate, carbon, and sulfur. The ingredients in smokeless powder are nitrocellulose and either nitroglycerin or nitrated cotton.

11. Why are some traces of the accelerants used in an arson usually found even after intense fires?

When an accelerant is poured over a large area, some of it will likely seep into porous surfaces such as cracks in the floor, upholstery, rags, plaster, wall boards, and carpet, where enough is it remains unchanged that it can be detected in the crime laboratory. In addition, when the fire is extinguished with water, volatile fluids may have operate more slowly as water cools and covers materials through which the fluids may have soaked.

10. What type of materials can be identified using X- Ray diffraction?

X-ray diffraction can be applied only to the study of solid, crystalline materials-that is, solids whose atoms have a definite and orderly arrangement.

2. Should you believe the owner's story, or should you suspect arson? Upon what do you base your conclusion? (passage on packet)

You should suspect arson. Although the conditions in which the oil was stored (high heat and lack of ventilation) may lead to spontaneous combustion with some materials, spontaneous combustion does not occur with hydrocarbon lubricating oils such as motor oil. He may have deliberately set the fire to collect insurance money.

What are the most widely used low explosives?

black powder and smokeless powder

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

color spot tests, thin-layer chromatography (TLC), and gas chromatography/mass spectrometry

16. List and define the three mechanisms of heat transfer?

conduction- movement of heat through a solid object radiation- transfer of heat energy from a heated surface to a cooler surface by electromagnetic radiation convection- transfer of heat energy by movement of molecules within a liquid or gas

20. A search of the fire scene must focus on finding a. traces of accelerant. b. ignition devices. c. human remains. d. the fire's point of origin.

d

15. As a fire progresses, toward what region does the heat created by combustion tend to move?

from a region of higher temperature to a region of lower temperature

What ingredients are required to create a low explosive?

fuel and a good oxidizing agent

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

infrared spectrophotometry and X-ray diffraction

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

the ion mobility spectrometer (IMS)

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

the presence of a crater at the origin of the blast

6. A fire will burn until either of which two components is exhausted?

until either the oxygen or the fuel is exhausted