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What are Explosions?• A sudden conversion of potential energy
(chemical or mechanical) into kinetic energy with a production and release of gases under pressure.
• Caused by a chemical reaction—either by
Explaining Explosions
• Kinetic molecular theory explains the properties of gases
• Combined Gas Law
Explaining Explosions
If the temperature of the enclosed gas increases and volume is held constant, the pressure _________
Explaining Explosions• Wave—
• Longitudinal wave—a pressure wave
• Shrapnel
Low Explsoives• Tend to react more slowly
• Deflagration—the resulting combustion reaction• Rapid, intense burning• Pressure waves at less than 340 meters / sec.
Explosives
Low Explosives
• Black powder • Smokeless gunpowder (nitrocellulose)
High Explosives
• Materials that • Detonates easily• Produces pressure waves to 8500
meters / sec.• Shock wave moves faster than speed
of sound• Detonation—
DETONATION
VAPOR CLOUD DEFLAGRATION
TIME
OV
ER
PR
ESS
UR
E
Pressure vs Time Characteristics
Detonation• Highly turbulent
combustion• Very high flame speeds• Extremely high pressures
>10 bars
Explosion Investigation
• Primary High Explosives• Extremely sensitive to heat, pressure,
and movement• Usually too volatile for most uses
• Secondary High Explosives• Less sensitive• Often used for military and commercial
purposes• TNT (trinitrotoluene)• dynamite • PETN (pentaerythritol tetranitrate) for
grenades• RDX (cyclotrimethlylenetrinitramine)
this is often found in moldable C4 explosives
Examples of Primary High Explosives
CH2OH
CHOH
CH2OH
CH2ONO2
CHONO2
CH2ONO2
HNO3
H2SO4
Glycerine Nitroglycerine
HOH2C C
CH2OH
CH2OH
CH2OH
HNO3
H2SO4
O2NOH2C C
CH2ONO2
CH2ONO2
CH2ONO2
Pentaerythritol Pentaerythritoltetranitrate(PETN)
Nitroglycerine
• Pure Nitroglycerine is way too “sensitive” to be a useful explosive. It was the invention of dynamite by Alfred Nobel that converted nitroglycerine into a useful commercial and military explosive by mixing nitroglycerine with clay (diatomaceous earth) and forming the mixture into dynamite sticks.
• nitroglycerin-based dynamite has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate-based explosives
CH2ONO2
CHONO2
CH2ONO2
12 CO2 + 10 H2O +
6 N2 + O2
Detonation4
Types of explosives
Amatols = mixtures of ammonium nitrate and TNT
ANFO = mixtures of ammonium nitrate and fuel oil
Organic Peroxides – A very different and less predictable class of potentially explosive compounds.
H3C O
O
O
H H O
O
O
H
O
O
O
O
O
O
O
OO
H
O
O
O
H
Perxyacetic Acid Peroxyformic Acid
Dibenzoylperoxide
Diethylperoxide
n-octyldiperoxysuccinic acid
Types of explosives
Acetone Peroxide• Formed from acid catalyzed
reaction of acetone with hydrogen peroxide.
• Extremely dangerous and unpredictable in it’s detonation behavior.
• Has been used by terrorists.- easily prepared from common chemicals which are not regulated.
- not detected by bomb-sniffing dogs.
• Diesel and Jet fuel tanks have a higher risk of explosion than automobile fuel tanks.
• TWA Flight 800 exploded in mid air in 1996, probably due to a vapor phase fuel tank explosion.
Types of explosives
“The July 17, 1996, crash of TWA flight 800, a Boeing 747 airplane, was blamed on a fuel-air explosion within the center wing tank, with the ignition source still unidentified. As a consequence of the accident, the Federal Aviation Administration (FAA) is evaluating improved safety requirements for the fuel tanks on commercial aircraft. One technique, recommended by the National Transportation Safety Board (NTSB), is to maintain sufficient fuel in the center wing tanks of transport aircraft to limit the liquid fuel temperature rise and evaporation, thus keeping the vapor fuel/air ratio below the explosive limit. Initial attempts to determine the benefit of additional fuel in the center tank were frustrated by the lack of an acceptable method for determining the explosive hazard in the tank under varying conditions.”
- FAA final report, TWA Flight 800 crash investigation.
• The result of a vessel failure in a fire and release of a pressurized liquid rapidly into the fire
• A pressure wave, a fire ball, vessel fragments and burning liquid droplets are usually the result
B L E VOILING
IQUID
XPANDING
XPLOSIONS
EAPOR
FUELSOURCE
Types of explosives
• An overpressure caused when a gas cloud detonates or deflagrates in open air rather than simply burns.
V C EUNCONFINED
APOR
LOUD
XPLOSIONS
Types of explosives
• Cloud will spread from too rich, through flammable range to too lean.
• Edges start to burn through deflagration (steady state combustion). Cloud will disperse through natural convection.
• Flame velocity will increase with containment and turbulence.
• If velocity is high enough cloud will detonate. If cloud is small enough with little confinement it cannot explode.
113257467
7561078
1513
12 5 10 1520 30 355065
PeakOverpressur
epsi
EquivalentWind Velocity
km/h
Knock personnel down
Rupture eardrums
Damage lungs
Threshold fatalities50% fatalities99% fatalities
Effects
Impact of Explosions on People
Explosion Impacts
0.5-to-11-to-2
2-to-33-to-4
57
7-8
PeakOverpressur
epsi Glass windows break
Common siding types fail:- corrugated asbestos shatters- corrugated steel panel joints fail- wood siding blows in
Unreinforced concrete, cinder block walls failSelf-framed steel panel buildings collapseOil storage tanks ruptureUtility poles snapLoaded rail cars overturnUnreinforced brick walls fail
Typical Damage
Impact of Explosions on Facilities
Explosion Impacts
Origin and Cause Analysis
Collection and analysis
Categorizations of Explosion Causes:• Accidental, unintentional and explainable• Undetermined, cause unknown or unable to be
identified• Incendiary, intentional act for profit or revenge• Terrorism
• One approach for screening objects for the presence of explosive residues in the field or laboratory is the ion mobility spectrometer (IMS).
• All materials collected for the examination by the laboratory must be placed in sealed air-tight containers and labeled with all pertinent information.
• Debris and articles collected from different areas are to be packaged in separate air-tight containers.
• It has been demonstrated that some explosives can diffuse through plastic and contaminate nearby containers.
Collection and analysis
Back at the Lab
• Typically, in the laboratory, debris collected at explosion scenes will be examined microscopically for unconsumed explosive particles.
• Recovered debris may also be thoroughly rinsed with organic solvents and analyzed by testing procedures that include color spot tests, thin-layer chromatography, high-performance liquid chromatography, and gas chromatography-mass spectrometry.
• Confirmatory identification tests may be performed on unexploded materials by either infrared spectrophotometry or X-ray diffraction.