Transcript Document

EXPLOSIVES:
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Effects of an
Explosion
Classification of
Explosives
Low Explosives
High Explosives
• Primary
• Secondary
Conclusion
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When an explosive is
detonated, the
material is instantly
converted from a
solid into a mass of
rapidly expanding
gases.
Causes 3 primary
effects:
• Blast pressure
• Fragmentation
• Thermal effects
Taken in part from a seminar by Jim Kahoe and Greg Brown
Effects of an Explosion: Blast Pressure
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At the time of detonation, the gases can
rush out at velocities of up to 7,000 mph
and can exert pressure of up to 700 tons
per square inch.
This gas travels in a outward circular
pattern like a giant wave, smashing and
shattering everything in its path.
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Effects of an Explosion: Fragmentation
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If a bomb is placed in an enclosed space, part
of the energy released will shatter the casing
and hurl them outward at 2,700 ft/sec.
Shrapnel – When objects are placed inside the
bulk of the explosive material. These will travel
faster then fragments because the energy that
would have been spent shattering the casing
is spent on propelling the shrapnel.
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Effects of an Explosion: Incendiary
Thermal Effect
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The least damaging of the three.
Varies from explosion to explosion.
• Low explosives burn slower producing longer
thermal effects then high explosives which
create a high amount of energy but for only
fractions of a second.
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Plays a bigger role when combustible
materials, such as gasoline, are used.
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Classification of Explosives
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The speed at which explosives
decompose enable explosives to be
classified into 2 categories.
• Low explosives – Velocity of detonation below
•
3,000 ft/s.
High explosives – Velocity of detonation
above 3,000 ft/s.
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Order of Priorities
Priority
Composition of Products of Decomposition
1
2
3
4
5
6
7
8
9
A metal and chlorine Metallic chloride(solid)
Hydrogen and chlorine HCl (gaseous)
A metal and oxygen Metallic oxide (solid)
Carbon and oxygen CO (gaseous)
Hydrogen and oxygen H2O (gaseous)
CO and oxygen CO2 (gaseous)
Nitrogen N2 (elemental)
Excess oxygen O2 (elemental)
Excess hydrogen H2 (elemental)
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Balancing Chemical Explosion Equations
* The progression is from top to bottom; you may skip steps that are not applicable, but you never back up.
* At each separate step there are never more than two compositions and two products.
* At the conclusion of the balancing, elemental forms, nitrogen, oxygen, and hydrogen, are always found in
diatomic form.
Example, TNT: C6H2(NO2)3CH3; constituents: 7C + 5H + 3N + 6O
Using the order of priorities priority 4 gives the first reaction products:
7C + 6O -> 6CO with one mol of carbon remaining
Next, since all the oxygen has been combined with the carbon to form CO, priority 7 results in:
3N -> 1.5N2
Finally, priority 9 results in: 5H > 2.5H2
The balanced equation, showing the products of reaction resulting from the detonation of TNT is:
C6H2(NO2)3CH3 -> 6CO + 2.5H2 + 1.5N2 + C
The number of moles of gas formed is 10. The product, carbon, is a solid.
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Volume of Products of Explosion
The molecular volume of any gas at 0 °C and under normal atmospheric pressure is very nearly 22.4
liters or 22.4 cubic decimeters. Thus, considering the nitroglycerin reaction.
C3H5(NO3)3 -> 3CO2 + 2.5H2O + 1.5N2 + .25O2
One mole of nitroglycerin produces 3 + 2.5 + 1.5 + .25 = 7.25 molecular volumes of gas; and these
molecular volumes at 0 °C and atmospheric pressure form an actual volume of 7.25 X 22.4 = 162.4
liters of gas. (Note that the products H2O and CO2 are in their gaseous form.)
Further, by employing Charles' Law for perfect gases, the volume of the products of explosion may also
be calculated for any given temperature. This law states that at a constant pressure a perfect gas
expands 1/273 of its volume at 0 °C, for each degree of rise in temperature.
Therefore, at 15 °C the molecular volume of any gas is,
V15 = 22.4 (1 + 15/273) = 23.63 liters per mol
Thus, at 15 °C the volume of gas produced by the explosive decomposition of one gram molecule of
nitroglycerin becomes
V = 23.63 l (7.25 mol) = 171.3 liters/mo
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Low Explosives
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Designed to burn or deflagrate
Used for military and civilian applications
Burning begins at one end of the charge
and travels with blinding speed through
the entire charge.
Primarily used as a propellant.
Black Powder
Smokeless Powder
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Black Powder
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Velocity of Detonation (VOD)
– 1,312 ft/s.
Composed of either
potassium nitrate or sodium
nitrate, charcoal, and sulfur.
History – Thought to
originate in China in the 9th
century for fireworks and
signals. Also evidence of
use in England around 1242
and by Arabs around 1300.
Smokeless Powder
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VOD – Similar to black
powder
Composed of nitrocellulose,
nitroglycerine, and various
stabilizers.
Currently makes up all of the
low explosives used for
propellants. Can be found in
the form of flakes, strips,
sheets, balls, or cords.
History – Was perfected in
1884 and first put to military
use by the French.
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High Explosives
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Detonate instead of burn
Designed to shatter and destroy
Initiated by blasting cap or detonator
Made up of 2 components:
• Primary high explosives
• Secondary high explosives
VOD as high as 27,500 ft/s
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Primary High Explosives
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Deliver an extremely sharp
shock to the explosive and
breaks the bonds of the
molecules of the material
and oxidizers. This initiates
the explosion.
Extremely sensitive to
shock, friction, flame, heat
or any combination.
High explosive trains and
boosters.
Used in blasting caps
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Types of Primary High
Explosives.
• Lead Azide – VOD –
16,745 ft/s.
• Lead Styphnate – VOD –
17,000 ft/s.
• Mercury Fulminate – VOD
– 14,780 ft/s.
• Diazodinitrophenel
(DDNP) – VOD – 21,700
ft/s.
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Secondary High
Explosives
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Relatively
insensitive
Manufactured for
military and
commercial use
• TNT
• Dynamite
• RDX
• ANFO
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TNTTrinitrotoluene
VOD-22,600 feet per second
Very stable among high
explosives
Relatively insensitive to blows
or friction
Used as booster charge for
high explosives
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RDX
Dynamite
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VOD-3,60023,600
feet/second
Uses:
construction,
road building,
quarrying,
mining
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VOD-26,800 
feet/second
White crystalline
solid
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Usually mixed
with other
explosives, oils,
waxes
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Compositions A,
B and C
ANFO
VOD-12,00015,000
feet/second
Mix of
ammonium
nitrate w/carbon
carriers
Uses:
construction,
road building,
and quarrying
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Instrumental Methods of Analysis
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IR can analyze for organics and nitrates
X-ray diffraction uses x-rays to analyze
powders of organic salts. Can reveal the
identity of salts
HPLC with ion selective detectors can
also detect inorganic components of
explosives
AA spectroscopy can reveal metal
components of residues
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Summary
EXPLOSIVES
LOW EXPLOSIVES
HIGH EXPLOSIVES
Black Powder
Smokeless Powder
PRIMARY HIGH
EXPLOSIVES
Lead Azide
Lead Styphnate
Mercury Fulminate
SECONDARY HIGH
EXPLOSIVES
BOOSTERS
PETN
RDX
MAIN CHARGE
DYNAMITE
WATER GELS
TNT
ANFO
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Sources
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DeHaan, John D. Kirk’s Fire Investigation. 4th Ed. Prentice Hall: New
Jersey, 1997.
Johnson, Jesse L. Explosives, Propellant Powders, and Related
Items. Office of Industries, U.S. International Trade Commission 1998.
National Institute of Justice. Guide for the Selection of Commercial
Explosives Detection Systems for Law Enforcement Applications. NIJ
Guide 100-99. U.S. Department of Justice 1999.
Nyden, Marc R. A Technical Assessment of Portable Explosives Vapor
Detection Devices. NIJ Report 300-89. U.S. Department of Justice
1990.
Saferstein, Richard. Criminalistics: An Introduction to Forensic
Science. 7th Ed. Prentice Hall: New Jersey, 2001.
http://www.sonic.net/~brucel/
http://siri.uvm.edu/ftp/ppt/blast1/tsld001.htm
http://www.ordnance.org/explosives.htm
http://www.fireandsafety.eku.edu/VFRE-99/Recognition/High/high.htm
http://www.fireandsafety.eku.edu/VFRE-99/#Introduction
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