Lecture 4: Investigation of Explosions Flashcards
Define explosion.
- Sudden and rapid escape of gases
- from a confined space
- high temperatures, violent shock, loud noise
- releases large amount of energy
- thermal
- kinetic (flying debris)
What are the common types of explosions?
- Nuclear explosion
- Mechanical explosion
- Chemical explosion
Chemical explosions are the most common and are induced by very rapid chemical reactions.
What distinguishes an explosive reaction from an ordinary combustion reaction?
The speed of the reaction. E.g. nitroglycerin reacts much faster than coal.
What is the typical gas production from an explosion per kilogram of explosive?
750 to 1000 liters of gas per kilogram of explosive
What is the Lower Explosive Limit (LEL)?
Lowest ratio of fuel to air at which the fuel mixture can propagate a flame.
Below LEL, no explosion will occur due to insufficient fuel.
What is Gay-Lussac’s Law?
The pressure of a gas is directly proportional to the temperature when the volume of the gas is constant.
P1/T1 = P2/T2, where T is in Kelvin.
What are low explosives?
- Materials that burn rapidly
- Explode only if contained
- Triggered by a flame
- Occurs in milliseconds
- e.g. black powder in gunpowder
What are high explosives?
- Produce a violent, shattering effect
- Can detonate without confinement
- Occur in microseconds
- INITIATING (primary)
- Sensitive to heat or shock
- Detonates other explosives
- E.g. nitroglycerin
- NON-INITIATING (secondary)
- Insensitive to heat or shock
- Need detonators like low explosives
- E.g. TNT
What is nitroglycerin?
A highly sensitive high explosive that can explode from physical shock.
It is also used as a heart medication (vasodilator).
What is the chemical structure of TNT?
2,4,6-trinitrotoluene.
Most used by the military in various munitions.
What is mass spectrometry?
- A scale for weighing tiny particles
- Identifies chemical substances by measuring their mass (mass to charge ratio)
What does the mass spectrometer consist of?
- Ion source
- Mass analyzer
- Detector
How is ionization achieved in mass spectrometry?
-
Electron ionization (EI)
- Removes an electron
- Uses 70 eV electron beam
- Needs heating for sample vaporization
- Only for volatile, thermally stable small molecules
-
Electrospray ionization (ESI)
- Attaches proton
- Almost no fragmentation
- No heating required
- For non-volatile, thermally unstable molecules
What are the goals of an explosion investigation?
- Identify victims
- Identify explosive
- Recover bomb and timing device
- Determine method of delivery
- Identify suspects
What is sought during explosion-related investigations?
- Explosive residues
- Bomb parts
(Helps to identify the explosive device)
What is the role of mass spectrometry in the analysis of explosives?
- Establish whether the sample contains an explosive
- Identify chemical nature of explosive
- Provide points of comparison between samples
- Establish link between suspect and crime scene
What is the process for quantifying a compound by mass spectrometry?
- Prepare series of solutions with known concentration
- Measure intensity due to standard solutions
- Construct a calibration curve
- Measure intensity of sample
- Read concentration from calibration graph
What is the purpose of constructing a calibration curve?
To measure intensity due to standard solutions against concentration.
What are the four components of the kinetic-molecular theory of gases?
- Gas particles are extremely small with relative distances between eo
- Gas particles act independently with no significant attractive/repulsive forces between eo
- Gas particles are in continuous random, straight line motion
- The avg kinetic energy of gas particles is proportional to the temperature of the gas
Explain the steps involved in mass spectrometer
- Ions pass metal plates with applied voltage → increased velocity
- Magnetic field is applied → deflected, travel in curved path
(larger mass-to-charge ratio → deflected less; smaller mass-to-charge ratio→ deflected more) - Measure mass-to-charge ratio for each sample
