1 / 17

Explosions: Types, Characteristics, and Collection of Evidence

Explore the different types of explosions and their characteristics, including low and high explosives. Learn about the collection of evidence following an explosion and the risks involved.

tgoldie
Download Presentation

Explosions: Types, Characteristics, and Collection of Evidence

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 5 Explosions

  2. Chapter Opener – Timothy McVeigh • After reading p. 132, answer the following questions: • 1. Investigators found several pieces of evidence linking Timothy McVeigh to the bombing. Why was it important that he was in custody on unrelated charges? • 2. What evidence was used to bring charges against McVeigh? • 3. Why do you think minimal physical evidence would be left behind after an explosion?

  3. Introduction • Use the information presented in Figure 5-3 on p. 134 to sketch a step by step diagram of a firecracker exploding. • Legal uses for explosives: • Mining • Demolition • Fireworks • Explosion = chemical reaction that releases a large amount of gas and energy very quickly • the chemical reaction is either an oxidation reaction or a decomposition reaction • Oxidation – two combine to make one • Decomposition – one is broken down into two or more • Ex) carbonic acid water and carbon dioxide

  4. Properties of Gases • http://www.media.pearson.com.au/schools/cw/au_sch_whalley_sf1_1/int/2_slg.html • http://www.harcourtschool.com/activity/states_of_matter/ • Kinetic vs potential energy - http://phet.colorado.edu/en/simulation/energy-skate-park • Kinetic molecular theory - http://www.youtube.com/watch?v=_rsqBNhFG1Y • Using the information presented in Fig. 5-4 on p. 135, sketch a before and after picture for each scenario presented

  5. Equation for combined gas laws P1 = 101.3 kPa P2 = 101.3 kPa V1 = 25 L V2 = ? T1 = 300 K T2 = 293 K

  6. Now try #15 and #16 on p. 152 • P1 = P2 = V1 = V2 = T1 = T2 = 16. P1 = P2 = V1 = V2 = T1 = T2 =

  7. Consider this scenario: You bought a cake and some balloons for a friend’s birthday. It was snowing outside, so you hurried to the car. By the time you reached the car, the a balloons were nearly dragging on the ground. Because the weather was really nasty, you didn’t want to go back into the store to exchange the defective balloons, so you hopped into the car, turned on the heat, and drove off. You had just about decided the cake was a good enough gesture when you noticed that the balloons were floating and blocking your view in the mirror. What on Earth was going on with these crazy balloons? Write a one-paragraph explanation of why the balloons deflated and then inflated once inside the car.

  8. Characteristics of an explosion An explosion does not require oxygen

  9. Instead….. * Energy and gases are released as the products of a chemical reaction. • The expanding gases produce a pressure wave. • http://video.nationalgeographic.com/video/news/astounding-video-of-volcano-shock-wave • Wave – a disturbance in matter that carries energy • Pressure wave – a kind of wave called a longitudinal wave – transfers energy • Compressions vs rarefactions – see Slinky demo • Explosions produce these waves and if in a closed container then container may burst and fragment • Flying debris = shrapnel

  10. Types of Explosives • Explosives - chemicals that react under certain conditions to cause explosions - most are solids - categories(based on rate of reaction) = low vs high • Low explosives – burn rapidly but explode only when confined in a container - produce a combustion reaction called deflagration - deflagration is a rapid, intense burning that produces a pressure wave that travels less than 340 meters/second - often used as propellants because it produces just enough gas and energy - Ex) smokeless gunpowder – nitrocellulose(cotton treated with nitric acid) - Ex) natural gas plus oxygen plus ignition – how are we protected?

  11. Types of Explosives High Explosives - materials that detonate Detonation – an explosion that results in a violent disruption to the surrounding area • Do not need to be confined to detonate • Ex) TNT – decomposition leaves behind black soot(evidence) • Pressure wave can travel up to 8,500 m/s called a shockwave • Used in the mining industry • Two categories of high explosives – a)primary and b) secondary • Primary – extremely sensitive to heat, pressure, and movement • - extremely dangerous to handle • Ex) nitroglycerin • Secondary – can be handled relatively safely but can cause very violent explosions • Ex) TNT and dynamite

  12. Safety precautions

  13. Classification By Use • Commercial – mining, road construction, and demolition • http://science.howstuffworks.com/engineering/structural/building-implosion1.htm • Military – Ex) RDX, PETN, and TNT • Improvised – low explosives placed in a confining container - illegal and often used by terrorists http://www.cnn.com/2015/11/09/middleeast/russian-plane-crash-egypt-sinai/

  14. Collection of Evidence • Explosion evidence is often destroyed in an explosion • Fire often follows an explosion • Collection of evidence can be dangerous • Risk of second explosion • 1. determine cause • 2. locate point of origin • 3. collect soil samples and debris • 4. test nearby objects for traces of explosive residue • 5. must maintain chain of custody • 6. evidence is packaged in metal or glass containers – why not plastic bags?

  15. Analysis of Evidence • Collected by field investigators • Sent to lab to identify type of explosive and mechanism used for detonation A) Microscopic Examination – look for unexploded material as well as pieces of the exploded device B) Color Spot Tests – look for reaction with a specific reagant – see Fig. 5-13 p. 142 3 presumptive tests – 1. Modified Griess Test 2. Alcoholic KOH 3. Diphenylamine Which test(s) would detect the presence of nitrate? Which test(s) would detect the presence of TNT? C) Chromatography - TLC(thin layer chromatography) or HPLC(high performance liquid chromatography) – compare residue samples with known samples D) Confirmatory tests – 1. infrared spectroscopy, 2. gas chromatography-mass spectroscopy

  16. Examination of Physical Evidence • Fingerprints • Explosive residue on clothes • Serial number on watch • Tool marks on pipes • Torn edges of duct tape

  17. Terrorism • Attacks are designed to cause injuries and death as well as scare people • Goals can be political, religious, environmental, or economic • Terrorism – the intentional use of force or violence to coerce or intimidate governments or other organized groups • September 11 attack • Domestic vs foreign terrorists

More Related