14-1 ©2011, 2008 pearson education, inc. upper saddle river, nj 07458 forensic science: an...

14-1©2011, 2008 Pearson Education, Inc. Upper Saddle River, NJ 07458

FORENSIC SCIENCE: An Introduction, 2nd ed.By Richard Saferstein

Warm-Up: December 3, 2014• How can fire debris help determine if a

fire was caused by arson?



Objective• SWBAT understand how explosives are

classified.



Agenda1. Follow the Case 4 & 5

2. OKC Bombing Documentary

3. Explosives

4. High vs. Low Explosives

5. Follow the Case

6. Exit Slip



Follow that Case

• http://www.interfire.org/features/followThatCase/episode001.asp



OKC Bombing Documentary

16. Who was McVey and Nicholls receiving funds from?

17. What do federal prosecutors believe caused the confusion of John Doe 2?

18. What was the most powerful piece of evidence?

19. What was McVey’s supposed motive?



ExplosionsA chemical explosive is a compound or a

mixture of compounds which, when subjected to heat, impact, friction, or shock, undergoes very rapid, self-propagating, heat- producing decomposition.



Explosions

Introduction to ExplosivesIntroduction to Explosives

• Most bombing incidents involve Most bombing incidents involve homemade explosive deviceshomemade explosive devices

• There are a great many types of There are a great many types of explosives and explosive devicesexplosives and explosive devices

• Lab must determine type of explosives Lab must determine type of explosives and, if possible, reconstruct the explosive and, if possible, reconstruct the explosive devicedevice

ExplosivesExplosives

• An explosive is a material that undergoes rapid An explosive is a material that undergoes rapid exothermic oxidation reaction (combustion), exothermic oxidation reaction (combustion), producing immense quantities of gas.producing immense quantities of gas.

• The build-up of gas pressure in a confined The build-up of gas pressure in a confined space is the actual “Explosion”. The space is the actual “Explosion”. The damage is damage is caused by rapidly escaping gases and caused by rapidly escaping gases and confinement.confinement.

• The ignition of an explosive is called DetonationThe ignition of an explosive is called Detonation

Explosives

• Combustion (or decomposition) of explosives occurs so rapidly, that there isn’t enough time for the oxygen in the surrounding atmosphere to combine with the fuel.

• Therefore, many explosives must have their own source of oxygen – or oxidizing agents



Shock Wave• It is this sudden buildup of gas pressure that

constitutes the nature of an explosion. • The speed at which explosives decompose

permits their classification as high or low explosives.

• Video: Rocket fuel production plant shock wave. http://www.youtube.com/watch?v=_KuGizBjDXo

Types of Explosives

• Low explosives• Combustion is relatively slow -1000 meters per

second• The speed of explosion is called the speed of speed of

deflagrationdeflagration• Crucial element is physical mixture of oxygen and fuel• Examples are black and smokeless powders

• Black powder is mixture of potassium nitrate, charcoal and sulphur

• Smokeless powder is nitrocellulose and perhaps nitro-glycerine

Black Powder (Low Explosive)• Black powder contains:

– 75% Potassium Nitrate (KNO3)– 15% Charcoal (C)– 10% Sulfur (S)

The KNO3 is the oxidizing agent. – When heat is applied to the powder, the

oxygen from KNO3 is liberated. – It combines with the carbon (fuel) and sulfur (for

stable combustion).– The combustion of charcoal and sulfur produces 2

gases – CO2 and N2.– The buildup of gases in the cartridge, propels the

bullet forward in bullet cartridges.

Black Powder Reaction

3C + S + 2KNO3 3CO2 + N2 + K2S + heatCarbon in charcoal

is fuel

Sulfur stabilizes

combustion

Saltpeter is the

oxidizing agent

Carbon dioxide gas

Nitrogen gas Potassium Sulfide solid

Smokeless Powder• Used as propellant in firearms and other weapons.

• There are 3 types:– Single-base – contains nitrocellulose– Double-base – contains nitrocellulose and nitroglycerine– Triple-base – contains nitrocellulose, nitroglycerine and

nitroguanidine

• Produce very little smoke when burned, unlike black powder.

• The reason that they are smokeless is that the combustion products are mainly gaseous, compared to around 55% solid products for black powder (potassium carbonate, potassium sulfate residues).



Gunpowder• The most widely used explosives in the low-

explosive group are black powder and smokeless powder. Burn rate is less than 3000 ft/second

• Black powder is a mixture of potassium or sodium nitrate, charcoal, and sulfur. Video

• Smokeless powder consists of nitrated cotton (nitrocellulose) or nitroglycerin and nitrocellulose. Video

Types of Explosives part deux• High explosives – they detonate (explode) rather

than deflagrate (burn)• Combustion can range from 1000 mps to 10,000 mps• Oxygen usually contained in fuel molecule

• Two types Initiating (or primary explosives)Initiating (or primary explosives)

• Sensitive, will detonate readily when subjected to heat or shock.

• Used to detonate other explosives in explosive train (a triggering sequence that ends up in a detonation of explosives)

• Includes Nitroglycerine Noninitiating (Secondary or base explosives) Noninitiating (Secondary or base explosives)

• relatively insensitive, to heat, friction or shock, need special detonators such as low explosives.

• Includes Dynamite, TNT or PETN

• ANFOs or (Ammonium Nitrate Fuel Oil) (These are actually tertiary)



Explosions• Among the high explosives, primary explosives

are ultra-sensitive to heat, shock, or friction and provide the major ingredients found in blasting caps or primers used to detonate other explosives. Examples are DDNP and lead azide. Web site

• Burn rates are 3000 –9000 ft/second.

Blasting Caps



DDNP• DDNP, an acronym for diazodinitrophenol, is a

picric acid derivative with somewhat good stability and explosive velocity. It is still

susceptible to heat, friction, and shock making it a primary explosive. Its preparation is very simple, needing only picramic acid, sodium or

potassium nitrite, and some dilute hydrochloric or sulfuric acid. This compound was first

prepared by Dr. Griess in 1858, and this led him to conduct ground breaking research on

the diazotization reaction.



Secondary Explosives• Secondary explosives are relatively insensitive

to heat, shock, or friction and will normally burn rather than detonate if ignited in small quantities in the open air. Dynamite & TNT, PETN, RDX

Diagram of dynamite.

1. Sawdust soaked in nitroglycerin.

2. Protective coating surrounding the explosive material.

3. Blasting cap.

4. Electrical cable (or fuse) connected to the blasting cap.



Dynamite• Dynamite is an explosive material based on

nitroglycern, initially using diatomaceous earth or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamite was invented by the Swedish chemist Alfred Nobel 1867. Remember Nobel Prizes?

• Dynamite is usually sold in the form of sticks about 8 in (20 cm) long and about 1.25 in (3.2 cm) in diameter, with a weight of about 0.5 lb (0.23 kg). Other sizes also exist.

• Dynamite is a high explosive, which means it detonates rather than deflagrates. While trinitrotoluene (TNT) is used as the standard for gauging explosive power, dynamite has more than a 60% greater energy density than TNT.



Explosions• This group comprises the majority of

commercial and military blasting, such as dynamite, TNT, PETN, and RDX.



High Explosives• In recent years, nitroglycerin-based dynamite

has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate–based explosives (i.e., water gels, emulsions, and ANFO explosives).

• Secondary explosives must be detonated by a primary explosive.



High Explosives• In many countries outside the United States,

the accessibility of military high explosives to terrorist organizations makes them very common constituents of homemade bombs.

• RDX is the most popular and powerful of the military explosives, often encountered in the form of pliable plastic known as C-4.



High Explosives• Triacetone triperoxide (TATP) is a homemade

explosive that has been used by terrorist organizations.

• TATP can be made by combining acetone and peroxide in the presence of an acid.

• Its existence has led to the banning of most liquids on commercial aircraft.

Nitroglycerin (Initiating or primary high explosive)Nitroglycerin (Initiating or primary high explosive)

• In its pure form, it is a contact explosive (physical shock can cause it to explode) and degrades over time to even more unstable forms.

• This makes it highly dangerous to transport or use.

• In this undiluted form, it is one of the most powerful high explosives, comparable to the newer military explosives

• Believe it or not, it is also used as heart medication – it is a vasodilator.

How does it work?

• The explosive power of nitroglycerin is derived from detonation: energy from the initial decomposition causes a pressure gradient that detonates the surrounding fuel.

Ingredients of Dynamite• Original dynamite consisted of three

parts nitroglycerin, one part diatomaceous earth and a small admixture of sodium carbonate.

• This mixture was formed into short sticks and wrapped in paper, with a “fuse” or a cord with a core of powder, that will transport the fire to the cylinder.

• Today, ammonium nitrate based dynamite is made and the fuse has been replaced with electronic detonators called blasting caps.blasting caps.

High Explosives Acronyms

• TNT = Trinitro Toluene

• PETN = PentaErythritol TetraNitrate, also known as pentrite. PETN is also used as a vasodilator, similar to nitroglycerin. Used as medicine for heart diseases.

• RDX = Cyclotrimethylenetrinitramine

• HMX or Octagon = Cyclotetramethylene-tetranitramine (related to RDX)

TNT (Non-initiating or secondary high explosive)TNT (Non-initiating or secondary high explosive)

• Trinitro Toluene

• Most used by the military

• Used in grenades, bombs, shells, or even alone.

PETN

• PETN and TNT used together to make small-caliber projectiles

• Commercially used (mining, demolition, etc.)

• PETN is used in detonation cords or Primacords. These cords are used to create a series of explosions.

PETN primacords attached to demolition explosives.

Ammonium Nitrate Based Explosives

• They are:

• Water gels

• Emulsions

• ANFOs (Ammonium Nitrate Fuel Oil)

Water GelsWater Gels

• Consistency of gel or toothpasteConsistency of gel or toothpaste• Water-resistant, so good for explosions in or Water-resistant, so good for explosions in or

under bodies of water and wet conditionsunder bodies of water and wet conditions• Contains:Contains:

– Oxidizers : a mixture of ammonium nitrate and Oxidizers : a mixture of ammonium nitrate and sodium nitrate, gelled together with a carbohydrate sodium nitrate, gelled together with a carbohydrate like guar gum (food thickener and emulsifier)like guar gum (food thickener and emulsifier)

– The fuel : is usually a combustible substance such as The fuel : is usually a combustible substance such as aluminumaluminum

Emulsion ExplosivesEmulsion Explosives

• Have 2 distinct phasesHave 2 distinct phases– An oil phaseAn oil phase– A water phaseA water phase

• These emulsions containThese emulsions contain– An ammonium nitrate solution (oxidizer) An ammonium nitrate solution (oxidizer)

surrounded bysurrounded by– A hydrocarbon (fuel)A hydrocarbon (fuel)– An emulsifier such as glass, resin or ceramic An emulsifier such as glass, resin or ceramic

microspheres to make the explosive less microspheres to make the explosive less sensitivesensitive

ANFO• Ammonium nitrate (oxidizer) or urea

nitrate, soaked in a highly combustible hydrocarbon (fuel) – usually a fuel oil.

• Easy to make, safe to handle

• Ammonium nitrate is found in fertilizers, so ANFOs are a favorite type of homemade bombs.

ANFOs in trucks

Dupont is a leading manufacturer of industrial and commercial ANFO

Homemade Explosives

• Molotov Cocktails

• TATP (Triacetone triperoxide) – a favorite amongst Middle Eastern Terrorists.

Molotov cocktail• In its simplest form, a Molotov cocktail is a glass bottle

containing petrol fuel usually with a source of ignition such as a burning, fuel soaked, rag wick held in place by the bottle's stopper.

• In action the fuse is lit and the bottle hurled at a target such as a vehicle or fortification. When the bottle smashes on impact, the ensuing cloud of petrol droplets and vapor is ignited, causing an immediate fireball followed by a raging fire as the remainder of the fuel is consumed.

• Other flammable liquids such as wood alcohol and turpentine have been used in place of petrol.

• Thickening agents such as motor oil have been added to the fuel, analogously to the use of napalm, to help the burning liquid adhere to the target and create clouds of thick choking smoke.



History of High Explosives• http://www.bing.com/videos/search?

q=chemistry+of+explosives&view=detail&mid=04419638D1DD42E4393D04419638D1DD42E4393D&first=0&FORM=NVPFVR#view=detail&mid=04419638D1DD42E4393D04419638D1DD42E4393D



Follow that Case

• http://www.interfire.org/features/followThatCase/episode001.asp



Homework• Read Chapter 13, pages 458-468, #14-20



Exit Slip: December 3, 2014Go to m.socrative.com and enter 417101

Question: What is the difference between low and high explosives?

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