What are Explosions?

1. 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

2. Explaining Explosions • Kinetic molecular theory explains the properties of gases • Combined Gas Law

3. Explaining Explosions If the temperature of the enclosed gas increases and volume is held constant, the pressure _________

4. Explaining Explosions • Wave— • Longitudinal wave—a pressure wave • Shrapnel

5. Explosives Low Explsoives • Tend to react more slowly • Deflagration—the resulting combustion reaction • Rapid, intense burning • Pressure waves at less than 340 meters / sec.

6. Low Explosives • Black powder • Smokeless gunpowder (nitrocellulose)

7. High Explosives • Materials that • Detonates easily • Produces pressure waves to 8500 meters / sec. • Shock wave moves faster than speed of sound • Detonation—

8. Explosion Investigation Detonation • Highly turbulent combustion • Very high flame speeds • Extremely high pressures >10 bars Pressure vs Time Characteristics DETONATION VAPOR CLOUD DEFLAGRATION OVERPRESSURE TIME

9. Primary High Explosives • Extremely sensitive to heat, pressure, and movement • Usually too volatile for most uses

10. Secondary High Explosives • Less sensitive • Often used for military and commercial purposes • TNT (trinitrotoluene) • dynamite • PETN (pentaerythritoltetranitrate) for grenades • RDX (cyclotrimethlylenetrinitramine) this is often found in moldable C4 explosives

11. Examples of Primary High Explosives

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 • nitroglycerin-based dynamite has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate-based explosives

13. Types of explosives Amatols = mixtures of ammonium nitrate and TNT ANFO = mixtures of ammonium nitrate and fuel oil

14. Types of explosives Organic Peroxides – A very different and less predictable class of potentially explosive compounds. 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.

15. Types of explosives • 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. “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.

16. Types of explosives B L E V E O I L I N G I Q U I D X P A N D I N G A P O R X P L O S I O N S • 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 FUEL SOURCE

17. Types of explosives U N C O N F I N E D V C E A P O R X P L O S I O N S L O U D • 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. • An overpressure caused when a gas cloud detonates or deflagrates in open air rather than simply burns.

18. Explosion Impacts Impact of Explosions on People PeakOverpressure psi EquivalentWind Velocity km/h Effects 113 257 467 756 1078 1513 Knock personnel down Rupture eardrums Damage lungs Threshold fatalities 50% fatalities 99% fatalities 1 2 5 10 15 20 30 35 50 65

19. Explosion Impacts Impact of Explosions on Facilities PeakOverpressure psi Typical Damage Glass windows break Common siding types fail: - corrugated asbestos shatters - corrugated steel panel joints fail - wood siding blows in Unreinforced concrete, cinder block walls fail Self-framed steel panel buildings collapse Oil storage tanks rupture Utility poles snap Loaded rail cars overturn Unreinforced brick walls fail 0.5-to-1 1-to-2 2-to-3 3-to-4 5 7 7-8

20. Collection and analysis Origin and Cause 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

21. Collection and analysis • 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.

22. 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.