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

OVE

RPRE

SSU

RE

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• nitroglycerin-based dynamite has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate-based explosives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

OH H O

O

OH

O

OO

O

OO

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/hKnock 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 AnalysisCollection 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.